4 introduction to uDig

Getting Started with JGRASS & GIS

Silvia Franceschi

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“Free Software ... you should think of ‘free’ as in ‘free speech,’ not as in “free beer.””

Richard Stallman


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Getting Started with JGRASS and GIS

Objectives

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InstallationJGrass can be installed on all operating systems in which Java Virtual Machine is active: windows linux macOSX

JGrass can be freely downloaded from the website:

www.jgrass.org

There are two types of installation:installation using the complete version of JGrassinstallation as a uDig plugin 4


http://www.jgrass.org

http://www.jgrass.org

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Installation of the Complete Version

The complete version of JGrass is only released for particular projects or for events such as the current

JGrass_foss4g

To install just click on the executable file and install JGrass in the desired location.

With this version GRASS tools are also supplied ready for execution.

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The JGrass uDig plugin can only be installed after the installation of uDig.Download the recommended version of uDig from http://udig.refractions.net/download/Install uDig following the on-screen instructionsSelect from the menu Help -> Find and Install...

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Installation as a uDig Plugin


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Select to install new features and follow the on-screen instructions.Select JGrass from the features to install.

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•The installation of JGrass in uDig adds three new menus to the menubar:

- Horton Machine

- JGrass

- GRASS

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Installation as a uDig Plugin•The installation of JGrass in uDig adds three new menus to the menubar:

- Horton Machine

- JGrass

- GRASS

•And two new icons to the toolbar:− open the scripting editor− define a work region


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Just as with JGrass, it is possible to install the Axios extension as a plugin in uDig or in JGrass. This adds tools for editing and modification of vector data (shp) to the GIS.

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Description of the Work Environment

PROJECT VIEW

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PLAN VIEW

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MAP VIEW

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CATALOGUE, ATTRIBUTES TABLE,...

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Data Viewing

In JGrass-uDig it is possible to view georeferenced data in either RASTER format or VECTOR format.

For the vector data the uDig features are used.

Further information on this (personalised viewing, network viewing of the data,...) can be found in the two manuals:

http://udig.refractions.net/confluence/display/EN/Walkthrough+1http://udig.refractions.net/confluence/display/EN/Walkthrough+2

For the raster data the features of both systems are used depending on the type of data being viewed.

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Creation of a New ProjectThe creation of a new project from imported data is automatic in uDIG. However, it is advisable to be coherent and ordered in the management of data by creating a new PROJECT where the desired MAPS can be stored.

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Project Name

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Creation of a New Project


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Location where new project will be saved

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Creation of a New Project


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Overview for Data Viewing

•uDig and JGrass work with Drag&Drop logic: all data can be

viewed simply by dragging them into the programme.

•Alternatively, the file can be dragged from Explorer onto:

•catalog: the plan is added to the catalogue but not viewed

•map: the plan is viewed and added on top of all viewed plans

•plan: the plan can be added at any point in the list of active

plans

•project: the plan is added to the open project

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To view a shapefile, from the family of shapfile files, select the file with .shp extension.Select the file in the computer’s Explorer and drag it to the Catalog of JGrass.Select the Catalogue tab and, with a right-click, select “Add to New Map”.Alternatively, it is possible simply to drag the file into the Map view.

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Overview for Vector Data


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Movement of the plans up and downModifying the view styleManaging the transparency between plansViewing the entire plan

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Tools for feature selectionQueriesEditing vector plans

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Map navigation toolsZooming and panning

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Raster data in image format (TIFF, JPG) can be viewed in JGrass-uDig in the same way as vector data.This data type, however, cannot be modified from within the programme. Its sole purpose is that of base cartographic reference.

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Overview for Raster Data


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Overview for Raster Data


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In JGrass, data must be organised and grouped according to a precise logic:DATABASE: a working directory on the hard disk where all data used and processed by JGrass for the various projects are stored.LOCATION: physically, this is a directory in the file system where information relative to the coordinate and projection system for the data is stored.MAPSET: physically, this too is a directory within the Location. It represents the JGrass workspace where the actual data are stored.

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JGRASS: Raster Data Analysis


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Immagine non modificabile.


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The data structure within JGrass is completely managed by the programme. The user only needs to define the DATABASE directory and the names of the LOCATIONS when these are created.The creation of a new Location is done from the menubar:

File -> New -> Other

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Pathname of the JGrass database

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Name of the new Location to be created

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Choice of Projection System

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Name of new Mapset

defined here

Click ‘add’ to create a new Mapset

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Drag the “.jgrass” file from the Location to the JGrass catalog

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Type of data that can be imported directly into

JGrass

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Reset updates the list of maps in the Mapset

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To view data from the JGrass Mapset it is advisable to create a new map. In this way the projection information is managed in the best way.Currently, vector data and raster images are projected “on the fly”. But the support for the re-projection of JGrass raster data is currently being developed.

Select, with a right-click on the name of the imported map, “Add to New Map”.

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An important concept in raster analysis is that of Active Region and Work Region.The Active Region represents the portion of area where all calculations will be carried out. That is to say the area where the GRASS-JGrass tools will work. In order to view the Active Region it must be dragged into the Map View from:

Catalog -> Map Graphics -> Active Region Graphic

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An important concept in raster analysis is that of Active Region and Work Region.The Active Region represents the portion of area where all calculations will be carried out. That is to say the area where the GRASS-JGrass tools will work. In order to view the Active Region it must be dragged into the Map View from:

Catalog -> Map Graphics -> Active Region Graphic

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If, in the Catalog, more than one Location has been loaded, or there are more than one Mapaset for a Location, it will be necessary to indicate to the programme which of the datasets to work with by selecting the Mapset from the appropriate dialog box.

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The Active Region is viewed, by default, as a white area on a green background.All the analyses carried out with the GRASS-JGrass

commands are only done on the Active Region and at its resolution.

Therefore, if there are no data in the white area, or if all the data are covered in green, then these data will not be processed.

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To modify the extension of the Active Region or the various options associated with it you can use:

the style editor button, starting by selecting the plan that represents the Active Regionthe icon in the toolbar: this will only modify the extension of the Active Region but not its resolution

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Click Apply twice!!!

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JGRASS: Work Environment Settings

The correct execution of JGrass requires the definition of two items:

Working Mapset: this is the Mapset that contains the data that is to be analysed (-> the Active Region that will be used during analysis is the one relative to the selected Mapset) ‏pathname for the GRASS tools: this is not necessary if you are only using native JGrass tools. It is indispensable, however, if you wish to use GRASS tools. Specifically, it refers to the GRASS installation pathname on your computer. With the complete version of JGrass the GRASS tools are included in the JGrass installation directory, and this is the directory to specify. In all other cases a separate installation of GRASS on your computer is required.

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JGRASS: Work Environment Settings


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JGRASS: General Tools

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Geomorphological Analysis in JGRASS: the Horton Machine Package

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Objectives:

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It has been developed with the purpose of proposing some quantitative and qualitative tools for the study of catchment morphology.

• Its main applications have been to alpine catchments of various dimensions (from a few Km2 to some hundreds of Km2)

• Applications have been made with different types of DEM (IGM 20m, PAT 10m, LaserAltimetriv 2m)

HORTON MACHINE: THE PURPOSE

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The starting hypothesis is:

HORTON MACHINE: OUR WORK

MORPHOMETRY EROSION PROCESSES

Based on this hypothesis, the purpose of the work is to analyse the erosion processes, the incision processes of the network, and the possibility of landslides. This is done by considering that the main geomorphological processes in a catchment are:

• Diffusive erosion on the hillslopes

• Network incision processes

• Landslides

• Sediment transport in the channels

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HORTON MACHINE: THE HISTORY

• Initially, the Horton Machine was a package of stand alone routines independent of an operating system, written in C using the FluidTurtle libraries and their input/output defined formats. The viewing of the calculated matrices was done with other graphical programs or with Mathematica;

• The second step was to integrate these routines into GIS-GRASS so as to have a direct graphical interface in TkTcl;

• Now, with the development of JGrass, these routines are being rewritten in Java and completely integrated into the new GIS system with a new development model (OpenMI) and new graphical interface.

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The tools are divided in 7 categories:

•DEM manipulation

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes•Network related measures

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes•Network related measures•Hillslope analyses

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes•Network related measures•Hillslope analyses•Basin attributes

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes•Network related measures•Hillslope analyses•Basin attributes•Statistic

HORTON MACHINE:

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•DEM manipulation•Basic topographic attributes•Network related measures•Hillslope analyses•Basin attributes•Statistic•Hydro-geomorphology

HORTON MACHINE:

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The topography is represented by a bivariate continuous function z = f(x,y) with continuous derivative up to the second order almost everywhere.

MORPHOLOGY

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The representation of data on a regular rectangular constitutes the most common and most efficient form in which the digital terrain data can be found.

DEM HYPOTHESIS:

•data are significant

•regular squared grid

•8 direction topology

DIGITAL ELEVATION MODELS (D.T.M.) ‏

In this raster form the data is usually made by reporting the vertical coordinate, z, for a subsequent series of points, along an assigned regular spacing profile.

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PRELIMINARY OPERATIONS

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PRELIMINARY OPERATIONSimport the starting DEM, which is to be

analysed, into JGrass

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define the working region

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pit detection


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definition of the drainage directions

D8 (maximum slope) ‏

D8 with correction(correction on the direction

of the gradient) ‏

import the starting DEM, which is to be analysed, into JGrass

pit detection


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of the gradient) definition of the main network‏


pit detection


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identification of the existing sub catchments

definition of the main network


pit detection


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extraction of the catchment of interest





identification of the existing sub catchments

definition of the main network


pit detection


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DERIVED ATTRIBUTES:

• Local Slope (h.slope)‏

• Local Curvature (h.curvatures or h.nabla)‏

• Total Contributing Area (h.tca, h.multitca) ‏

• Catchment Divide Distance (h.hacklength)‏

• Distance to Outlet (h.distance2outlet) ‏

………..

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FIRST STEP: DEPITTING THE DEM

The first necessary operation is to fill the depression points that are present within a DEM so that the drainage directions can be defined in each point.

Observations on this topic demonstrate that this calculation addresses fewer than 1% of the data: usually these depressions are present because of wrong calculations during the DEM creation phase and are not, in fact, real depressions in the terrain.

The command used to fill the depressions is:

h.pitfiller

This tool is based on the Tarboton algorithm.

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h.pitfiller

Fills the depressions in the DEM according to the Tarboton algorithm.

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FLOW DIRECTIONSFlow directions define how water moves along the surface in relation to the topology of the study region. From the flow directions it is possible to calculate the drainage directions.

Hypothesis: each DEM cell only drains to one of its 8 neighbours, either adjacent or diagonal, in the direction of the steepest downward slope.

only 8 possible directions in which the flow can be directed

this is a limitation of the model representation with respect to the

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h.flowdirections

This tool calculates the flow direction on the basis of the steepest downward slope, assigning to each DEM cell one of its 8 neighbours.

The flow directions numbering convention numbers from 1 to 8 in an anticlockwise direction with 1 being east.

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FLOW DIRECTIONS

In the map each colour represents one of the 8 drainage directions. The

image also shows the flow directions numbering

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FLOW DIRECTIONS

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Ho cambiato la direzione di alcune frecce qui a lato: da controllare!



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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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FLOW DIRECTIONS

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A CORRECTION TO THE PURE D8 METHOD

Using the “pure” D8 method, the drainage directions that are estimated deviate from the real drainage direction as identified by the gradients.

The “corrected” algorithm calculates the drainage direction minimising the deviation of these from the real flow direction. The deviation is calculated from the pixels at the highest elevations and carried through going downstream.

The deviation is calculated with a triangular construction and can be expressed either as angular deviation (method D8-LAD) or as transversal distance (method D8-LTD) .‏

The lambda parameter is used to assign a weight to the correction made to the drainage directions.

This method has been developed by S. Orlandini

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h.draindir

LAD method:

angular deviation check on alpha

LTD method:

transversal deviation check on delta

The deviation is cumulated from up-hill pixels. The D8 drainage direction is redirected to the real direction when the value of deviation is larger than an assigned threshold.

If λ = 0 the deviation counter has no memory and the up-hill p i x e l s d o n o t a f f e c t t h e calculation. 86



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THE NEW DRAINAGE DIRECTIONS &THE NEW TCA

STANDARD METHOD

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What is TCA?Total Contributing Area, ma non si vede fino alla diapositiva 98.



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STANDARD METHOD

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STANDARD METHOD

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STANDARD METHOD

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STANDARD METHOD

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h.draindir

Map obtained categorising the results of the drainage directions tool

Map obtained personalising the colours of the original map

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What does the 10 value signify - no flow?



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h.draindirFIXED NETWORK METHOD: in flat areas or where there are manmade constructions, it can happen that the extracted channel network does not coincide with the real channel network.

Fixed network

Extracted network

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h.draindir

FLOW FIXED METHOD

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Flow fixed map created byh.netshapetoflow from a

shapefile of the network

h.draindirFLOW FIXED

METHOD

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Fixed network

Extracted network

h.draindir

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Fixed network

Extracted network

h.draindir

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TOTAL CONTRIBUTING AREA

The Total Contributing Area is precisely this: it represents the total area that contributes to a particular point of the catchment basin.

It is an extremely important quantity in the geomorphological and hydrological study of a river catchment: it is strictly related to the flows passing through the different points of the system in uniform precipitation conditions.

Most of the diffusive methods used to extract stream networks from digital models are based on this quantity.

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TCA

Where Wj is:

• 1 for pixels that drain into the i-th pixel;• 0 in any other case for single flow directions.



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TCA

Where Wj is:


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source

TCA

Where Wj is:


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source

TCA

Where Wj is:


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TCA

Where Wj is:


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source

TCA

Where Wj is:


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source

TCA

Where Wj is:


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1 source

TCA

Where Wj is:


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2

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TCA

Where Wj is:




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source

2

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TCA

Where Wj is:




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source

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TCA

Where Wj is:




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1 source

2

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TCA

Where Wj is:




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2

TCA

Where Wj is:


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source

2

TCA

Where Wj is:


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source

2

TCA

Where Wj is:


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1

3

source

2

TCA

Where Wj is:


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TCA

Where Wj is:


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source

TCA

Where Wj is:


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source

TCA

Where Wj is:


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1

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TCA

Where Wj is:


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TCA RESULTS COMPARISONLog(TCA) ‏ Log (LAD-TCA) ‏

The figures compare the total contributing areas calculated with the pure D8 method (left) and with the corrected LAD-D8 method (right). In this latter case the typical maximum steepest parallelisms are not present with a representation of the flow very near to reality. 105

La parte in neretto non l’ho toccata perche’ non mi e’ chiara - da revisionare dall’autore.



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h.markoutlets

The correct execution of many applications within JGrass requires a matrix of the flow directions that have a new additional class value. This new class (conventionally indicated in JGrass with 10) identifies the basin outlets, i.e. those pixels that drain to outside the analysed region.

The tool that assigns this new class value marks the outlets:

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h.markoutlets

The correct execution of many applications within JGrass requires a matrix of the flow directions that have a new additional class value. This new class (conventionally indicated in JGrass with 10) identifies the basin outlets, i.e. those pixels that drain to outside the analysed region.

The tool that assigns this new class value marks the outlets:

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GRADIENTSThe gradients are relevant because the main driving force of the flow is gravity. The gradient identifies the flow directions of the water and also it contributes to determining the flow velocity.It must be observed that the gradient tool, unlike the slope tool, does not use the drainage directions. It calculates only the module of the gradient. The gradient is in reality a vectorial quantity oriented in the direction from minimum potential to maximum potential.

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h.gradients

The sub-surface flow is proportional to the slope while the surface runoff is proportional to the root of the slope. Erosion, and the resulting sediment transport, depend on the gradients of the topographic surface. Furthermore, areas with elevated slope values are generally devoid of soil, being made up of exposed rock.

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We can see the deep network incision and the flat area near the basin

outlet.

The obviously wrong calculation in the upper part of the basin is due to the joining of DEMs

that were originally square in shape.

GRADIENTS

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The gradient calculated with this tool is given as the tangent of the corresponding angle. Using the MAPCALCULATOR it is possible to obtain the map of the gradients expressed in degrees

h.gradient

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The gradient calculated with this tool is given as the tangent of the corresponding angle. Using the MAPCALCULATOR it is possible to obtain the map of the gradients expressed in degrees

h.gradient

atan(gradient) ‏

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This tool estimates the slope in every point by employing the drainage directions. Differently from gradient, slope calculates the drop between each pixel and the adjacent points below. The resulting measure of drop is divided by the pixel length, along its side or its diagonal according to the cases.The greatest value is the one chosen as slope.

SLOPE

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h.slope

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CURVATURE

Curvature is a measure of the deviation per unit length of the gradient vector along a curve, f(x,y), marked on the surface under study.The Longitudinal Curvature represents the deviation of the gradient as one moves from upstream to downstream along the envelope of the gradients.The Plan Curvature is what is obtained when the surface is intersected with a plane parallel to the (x,y) plane. It is the variation of the vectors tangent to the contour line passing through the point under study. The Tangential Curvature is determined by the intersection curve defined by a plane perpendicular to the gradient direction and tangent to the contour line at the point.

The tangental and plane curvature are proportional to each other and the spatial distribution is the same.

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THE CURVATURES

The mathematical definition is quite complex.

Longitudinal curvature Plan curvature

it represents the deviation of the gradient along the flow

(it is negative if the gradient increases) ‏

it represents the deviation of the gradient along the transversal direction

(i.e. along the contour lines) ‏

it measure the convergence (+) or divergence (-) of the flow

N.B. Convex sites (positive curvature) represent convergent flow, concave sites (negative curvature) represent divergent flow.

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NORMAL/TANGENTIAL CURVATURE

Negative - convex curvature: this case is typical in slope areas where the flow is subdivided amongst the neighbouring pixels with lower e l e v a t i o n b y m e a n s o f t h e maximum slope.

Locally divergent topography

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h.curvature

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h.curvaturesLongitudinal Curvature Plan Curvature

Plan curvatures separates the concave parts from the convex ones

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TOPOGRAPHIC CLASSIFICATIONIt is a means of subdividing the sites of a catchment according to 9 topographic classes defined by the longitudinal and transversal curvatures.

The 9 classes are grouped into 3 fundamental typologies:

•CONCAVE SITES •CONVEX SITES•PLANAR SITES

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h.tc

The program requests the input of the threshold values of the longitudinal and normal curvatures which define their planarity.

THE VALUE IS STRICTLY RELATED TO THE TOPOLOGY119



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h.tc

This tool produces two different maps as output: one with the 9 topographic classes and the other with the 3 typologies. For the 9 topographic classes the tagging convention is the following:

10 planar – planar sites20 convex – planar sites30 concave – planar sites40 planar – convex sites50 convex – convex sites60 concave – convex sites70 planar – concave sites80 convex – concave sites90 concave – concave sites

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h.tc

The map with the 3 typologies contains an grouping of these topographic classes into the three fundamental typologies:

15 concave sites (classes 30, 70, 90) ‏25 planar sites (classes 10) ‏35 convex sites (classes 20, 40, 50, 60, 80) ‏

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h.tc 9 classes h.tc 3 typologies

h.tc

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CHANNEL NETWORK EXTRACTION

3 METHODS ARE IMPLEMENTED

• threshold value on the contributing areas: only the pixels with contributing areas greater than the specified threshold are defined as channel heads‏

• threshold value on the shear stress at the bottom: threshold value assigned to the ratio between the total contributing area and the gradient

• threshold value on the shear stress only in convergent sites

HOW IT WORKS: As soon as the first pixel of the channel network is identified (i.e. the pixel in which the parameter value is greater than the assigned threshold) all the other pixel downstream of it are part of the channel network.

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h.extractnetwork

Threshold on the tca

The threshold depends on:

- dimensions of the pixels

- topographical attributes

1°method

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The threshold is on the parameter:

which is proportional to the shear stress at the bottom.


- pixels dimensions


2°method

h.extractnetwork

Non riesco a leggere l’immagine.



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Threshold on the tca of the concave sites.


- pixel dimensions


3°method

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In the resulting raster map the network pixels have been assigned the 2 value. Outside the network there are null values.

1°method: threshold on the tca

h.extractnetwork

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2°method: threshold on the product between the

tca and the gradient

h.extractnetwork

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3°method: threshold on the tca in the concave

pixels

In this case there are various groups of stream networks, each one of which corresponds to a catchment.

h.extractnetwork

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EXTRACTION OF THE WORKING CATCHMENT• first, define the catchment outlet:

•insert the known coordinates of the point•use the Query raster tool to select a point directly on the network map and verify that it is on the network (i.e. has a value of 2). •the coordinates of this point will be copied to the clipboard•use the coordinates of the selected outlet in the h.wateroutlet command

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JGrass generates two maps:

• the mask of the extracted catchment

• a chosen map cut on the mask

h.wateroutlet

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h.wateroutlet

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‣ h.pitfiller

‣ h.flowdirection

‣ h.draindir

‣ h.wateroutlet

‣ h.gradient

‣ h.curvatures

‣ h.tc

‣ h.extractnetwork

MORPHOLOGICAL ANALYSIS OF A CATCHMENT

The first step is to execute all the commands seen so far, but only to the extracted catchment. An alternative method would be to cut the existing maps along the mask of the extracted catchment using the mapcalculator command.

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‣ drainage directions‣ total contributing area‣ extracted network‣ gradient‣ curvatures‣ topographic classes‣ slope

The best thing to do is to cut the original maps along the mask of the extracted catchment. The maps to cut are the following:

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MORPHOLOGICAL ANALYSIS OF A CATCHMENT



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It calculates the drainage area per unit length (A/b), where A is the total upstream area and b is the length of the contour line which, it is assumed, drains area A. The l e n g t h o f t h e c o n t o u r affected is estimated by a novel method based on curvatures.

h.ab

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It calculates the drainage area per unit length (A/b), where A is the total upstream area and b is the length of the contour line which, it is assumed, drains area A. The l e n g t h o f t h e c o n t o u r affected is estimated by a novel method based on curvatures.

h.ab

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h.ab

The stream network pixels are concave sites.

• concave sites convergent sites• convex sites divergent sites

The contour line is locally approximated to an arc with radius inversely

proportional to the local planar curvature

b ~ t'

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h.ab

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The higher values of A/b are registered on or near the channel network.

In fact, these are the points for which the contributing area is the highest and the value of b is the lowest.

THE RESULT OF A/b

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THE RESULT OF A/b CHANGING THE COLOURMAP

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ASPECT

The aspect is defined as the inclination angle of the gradient. The conventional reference system puts the angle to zero when the gradient is orientated towards east and it grows in an anticlockwise direction.

The angle is calculated in radians.

Mathematically, aspect is defined by the following formula:

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h.aspect

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h.aspect

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h.aspect

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h.aspect

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N.B. Concave sites (positive curvature) imply converging flows, convex sites (negative curvature) imply diverging flows.

The laplacian is a close relative of the curvatures and gives a way to distinguish, in a first iteration, convex sites from concave sites within the catchment.

Mathematically, the laplacian is defined as:

THE LAPLACIAN

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Nota a pie di pagina contrasta con quella di slide 114 - questa mi sembra giusta, da controllare.



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Digital terrain data do not return reliable curvature values. On the other hand, the sign of the laplacian is sufficiently correct.

h.nabla

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convex element

flat element

concave elementPositive curvature

Negative curvature

Null curvature

DEFINITIONS OF CURVATURES

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h.nabla

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h.nabla

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This tool subdivides the sites of a catchment into 11 topographical classes. Nine of these classes are those obtained with TC.

h.gc

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It subdivides the sites of a catchment into 11 topographical classes: nine of these classes are those obtained with TC;the points belonging to the channel networks constitute a tenth class

(derived from use of the ExtraNetwork command)the points with high slope values (higher than a critical value)

constitute an eleventh class.

h.gc

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It subdivides the sites of a catchment into 11 topographical classes: nine of these classes are those obtained with TC;the points belonging to the channel networks constitute a tenth class

(derived from use of the ExtraNetwork command)the points with high slope values (higher than a critical value)

constitute an eleventh class.

h.gc

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h.gc

The reclassification of the topological classes is: 15 non-channel valley sites 25 planar sites 35 channel sites 45 hillslope sites 55 unconditionally unstable sites

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THE HACK LENGTH

It is given, assigned a point in the catchment, by the projection of the distance from the catchment divide along the network (while it exists), and then, proceeding upstream along the lines of maximum slope.

For each network confluence, the direction of the tributary with the greater contributing area is chosen. If the tributaries have the same area, one of the two directions is chosen randomly.

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THE HACK LENGTH

It is given, assigned a point in the catchment, by the projection of the distance from the catchment divide along the network (while it exists), and then, proceeding upstream along the lines of maximum slope.

For each network confluence, the direction of the tributary with the greater contributing area is chosen. If the tributaries have the same area, one of the two directions is chosen randomly.

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h.hacklentgh

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The magnitudo of a point is defined as the number of sources upstream to that point. It can be defined for every point of the catchment.

If the river network is a trifurcated tree (a node in which three channels enter and one exits), then there is a bijective correspondence between the number of sources, or springs, and the number of channels, defined as follows:

hc = 2ns − 1

hc is the number of channels

ns the number of sources

The mangitudo is also an indicator of the contributing area.155

MAGNITUDO: h.magnitudo



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MAGNITUDO: h.magnitudo

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NETNUMBERING

This tool assigns numbers to the network connections.

It can be used by the hillslope2channelattribute tool to label the hillslopes that are contributing to a section of the network with the same connection number.

Hence, it subdivides the basin into the hillslope areas that contribute to each connection.

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Please review; original English version not very clear.



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SUB-CATCHMENT EXTRACTION: h.netnumberingThe sub-catchments depend on the complexity of the network:a complex network has a large number of sub-catchmentsa simple network has a small number of sub-catchments

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SUB-CATCHMENT EXTRACTION: h.netnumberingThe sub-catchments depend on the complexity of the network:a complex network has a large number of sub-catchmentsa simple network has a small number of sub-catchments



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DISTANCE FROM THE NETWORK

This tool evaluates the distance of every pixel in the catchment from the network. It can work in 2 different ways:

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h.hillslope2channeldistance

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• calculates the distance in pixels• calculates the distance in metres

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• calculates the distance in pixels• calculates the distance in metres

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This tool calculates the distance, as projected onto the plane, of each pixel from the outlet, measured along the drainage directions.

It can work in two ways: it can calculate the distance from the outlet either in number of pixels (0:topological distance mode), or in metres (1:simple distance mode).

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DISTANCE TO THE OUTLET



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It calculates the rescaled distance of each pixel from the outlet. This distance is defined as:

x0 = xc + rxh

where: xc is the distance along the channels,

r = c/ch is the ratio between

c, the speed in the channel state, and

ch, the speed on the hillslopes

xh the distance along the hillslopes.

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Distances to outlet map for a simple channel network

Distances to outlet map with different velocities in channels and

hillslopes 164




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ANALYSIS OF THE VALUES OF A MAP: h.cb

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calculates the histogram of the values of a map with respect to those contained in another map

the data of the first map are grouped into a pre-fixed number of intervals and the average value of the independent variable is calculated in each interval

to each interval there corresponds a set of values in the second map for

which the average is calculated, as well as any other statistical moments

requested by the user

the output of this tool is a file, not a map

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maps on which calculation should be carried out: the second map can be the same as the first

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statistical moments to be caculated: average, variance, ...

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number of intervals in which to divide the range of values of the first map

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type and pathname of the output file

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it is possible to select to view the output data either in graph or table format

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it is possible to edit the graph and save it by right-clicking on the image and selecting the required operation

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The complete h.cb output file contains: the number of pixels from the first map contained in an interval the average value of the values of the first map contained in each

interval the average value of the values of the second map contained in

each interval the variance of the values of the second map in each interval moments of higher order calculated for the values of the second

map

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It expresses the tendency of pixel to become saturated

Areas with elevated values of the topographic index become saturated

before areas with lower values of the topographic index

It depends only on the morphology

It is proportional to the ratio of cumulated contributing area at the

pixel and slope

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TOPOGRAPHIC INDEX



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TOPOGRAPHIC INDEX: h.topindex



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there are some areas within the catchment where the topographic index is not defined

these are the areas with zero slope where, as a consequence, the ratio of

cumulative contributing area over slope tends to infinity

pixels with a small slope have a higher tendency to saturation than

pixels with a high slope under similar conditions of contributing area

the pixels with the lowest value of the topographic index are assigned

the highest characteristic value of the map

if(mybasin ,if(isnull(mybasin_topindex ),17.8,mybasin_topindex ) ,null

() )

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stringa di codice ????



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NUMBERING THE NETWORK: h.strahler

It calculates the Strahler order of the basin. There are two possibilities:

λ calculate the Strahler order for the entire basinλ calculate the Strahler order only for the network

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EUCLIDEAN DISTANCE: h.dist_euclidea

It calculates the euclidean distance of each pixel from the outlet of the

basin which contains it.

The flow directions map needed here is the one with the outlet marked.

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Thank you for your attention.

G.U

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Education

4 introduction to uDig