3D GIS DATA set GEPSUS-TERRA Manual: Description, Installation … · 2014. 12. 4. · 3D modelling and DSM/DTM generation For the generation of the dense 3D point cloud, an advanced

Terra Messflug GmbH

A-6460 Imst, Eichenweg 42

Terra Messflug GmbH

Eichenweg 42, 6460 Imst, Austria In Italia: Tel.: +43 (0) 5412/69 30-0 P.zza Duomo, 30, Trento Fax: +43 (0) 5412/69 30-26 P.IVA:ATU63650409 Tel. +39 345 4636699 email: [email protected] Direttore: Dipl. Ing. Roman Markowski

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3D GIS DATA set GEPSUS-TERRA Manual:

Description, Installation and Interfacing

Authors:

Daniela Poli, Klaus Legat, Kjersti Moe, Erik Bollmann

Terra Messflug GmbH, Austria

Imst, 12th November 2014

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TABLE OF CONTENT 3D GIS DATA set GEPSUS-TERRA Manual: Description, Installation and Interfacing ...................................... 1

1. Aerial image acquisition .................................................................................................................................................... 3

2. Image processing .................................................................................................................................................................. 4

Image preparation .................................................................................................................................................................... 4

Image orientation ...................................................................................................................................................................... 6

3D modelling and DSM/DTM generation ........................................................................................................................ 6

Orthophoto production ........................................................................................................................................................... 7

3. Delivery ..................................................................................................................................................................................... 8

4. Installation and interfacing with GEPSUS .................................................................................................................. 8

5. Training and support .......................................................................................................................................................... 8

Appendix I. Visualisation of point cloud data (*.las) and orthoimages / DSM (*.tif)

using different software products - Sample data from Trento Project 2014 ........................ 9

1. Visualisation of *.las Files .................................................................................................................................................. 9

Software: Global Mapper v15.2 ........................................................................................................................................... 9

Software: Cloud Compare v2.5.3 ...................................................................................................................................... 11

SOFTWARW: SAGA-GIS 2.0.8 ............................................................................................................................................. 12

Software: LasTools ................................................................................................................................................................. 13

Software: ArcMap 10.0 ( ArcGIS) ..................................................................................................................................... 16

2. Visualisation of *.tif Files (Orthophoto or DSM) ................................................................................................... 19

Software: Global Mapper v15.2 ........................................................................................................................................ 19

Software: ArcMap 10.0 ......................................................................................................................................................... 21

Import Orthophotos: ........................................................................................................................................................ 21

Importing DSM into ArcGis ............................................................................................................................................ 25

Software: QGIS 2.6.0 ......................................................................................................................................................... 30

Software SAGA-GIS 2.0.8: ............................................................................................................................................... 32

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1. Aerial image acquisition

The Cluster 4 - Trento products were generated using aerial images and rigorous photogrammetric methods. The aerial images of Trento were acquired on 23 September 2013 under optimal weather conditions, with

the aircraft Cessna C303 (Figure 1) and the large-format digital camera Vexcel UltraCam-Xp (Figure 2). The images have mean ground resolution (GSD) of 10 cm and large forward and side overlap (80% and 60%,

respectively), thus allowing the use of dense image matching algorithms for highly detailed 3D point cloud

generation and true-orthophoto production. The images cover the major part of the city of Trento, with approx. 18 km² in urban areas and 37 km² in

rural areas (Table 1 and Figure 3). The KML/KMZ file with the image extent was delivered.

Figure 1. Aircraft C303 Figure 2. Vexcel UltraCam-Xp

Table 1. Characteristics of the image flight and camera.

Digital camera Vexcel Ultracam-Xp, calibration 2013

Average GSD 10 cm

Along-track overlap 80%

Side overlap 60%

Number of strips 9

Number of images 397

Spectral channels Red, Green, Blue, Near Infrared

Radiometric resolution 12 bit

Date of acquisition 23 September 2013

Area covered by the flight 55 km²

Urban area covered by the flight 18 km²

Image format 17310 x 11310 pixels

Focal length 100,5mm

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Figure 3. Plan of Trento flight.

2. Image processing

The workflow followed for image processing is summarized in Figure 4.

Figure 4. Workflow for Trento data production.

Image preparation

First the images, which are taken with 8 lenses are stitched together. In this process, a pan-sharpening of

the imagery is undertaken, resulting in 4 band imagery with high resolution. All image processing is undertaken with UltraMap software by Vexcel. Further, the radiometry between the images is balanced.

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Initially, a project-wide automatic radiometric adaptation is undertaken (project-based color balancing). In

order to achieve optimal homogeneity within the project, each image is checked manually and the radiometry is adjusted by an experienced operator. The figure below demonstrates the main processing

steps undertaken to create uniform radiometric product (Figure 5). The operation was executed automatically with manual intervention to assess the transformation parameters.

Figure 5. Two-step radiometric processing. Example with imagery from Graz.

Parallel to the image processing, the flight trajectory with the projection centers are calculated. During the flight, a combination of dual frequency GPS-reciever NovAtel OEM I/IV and the inertial platform IGI IMU-lld

was used for the direct observation of the camera position and attitude for each exposure. After the flight, the trajectories were processed with differential technique (DGPS) with two master stations positioned near

the project area, thus ensuring that no images are acquired at a distance larger than 50km from the master

station. The GPS trajectory post-processing was executed with the software GrafNav, as seen in Figure 6, after differential processing of the GPS trajectory, the GPS and INS data were integrated with the software

AEROoffice by IGI GmbH.

Figure 6. Trajectory estimated after GPS post-processing.

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Image orientation

The geometric calibration of the camera was executed May 2013 by the camera producer based on a photo flight executed in an image block pre-defined for this purpose. The data processed with UltraMap 3.1.

Software by Vexcel Imaging GmbH. The operations included pre-processing, automatic tie-point extraction, initial bundle block adjustment and quality control.

The exact exterior orientation of each image (position and attitude angles) was estimated based on the

GPS/INS trajectory in a bundle block adjustment with the software Match-AT by Inpho. For this purpose, the coordinates of a suitable number of points were surveyed with ground measurements at centimeter

accuracy.

3D modelling and DSM/DTM generation

For the generation of the dense 3D point cloud, an advanced solution for dense image matching was used,

that allows getting a point cloud density up to every image pixel. In case of Trento, a density up to 100 points /m2 was reached. The point could was delivered in tiles with size 200m x 200m, that is 4 million

points per tile. The average accuracy of the 3D point cloud (+/- 1sigmaa) is 1 x average GSD in planimetry and 2 x average GSD in altimetryb. The 3D point clouds were rasterized into a digital surface model (DSM)

with grid 10cm (Figure 7).

For the digital terrain model (DTM) generation, the points were classified automatically in ground – not ground using the Lidar tool TerraScan by TerraSolid and rasterized in a 2m grid surface. In the point cloud

data sets, Ground has class 2. Remaining classes are not ground.

Figure 7. DSM on Trento city center, 10cm grid.

a Root mean error, referred to a normal Gaussian distribution of the measured values. b Theoretical value valid in open areas. Accuracy degrades in the same areas (not checkable): dark shadows

in narrow streets, moving objects (ex. cars, pedestrians), water surfaces, semi-transparent objects (i.e. glass

roofs), occlusions.

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Orthophoto production

Given the large overlap and the availability of a very dense DSM, true-orthophotos were generated (Figure 8). In case of conventional orthophotos, aerial images are rectified using the terrain model (DTM), so the

geolocation of points lying on the terrain is correct, but points above the terrain, like building roofs or building facades, are displaced (Figure 9). In case of Trento, the aerial images were projected orthogonally

on the DSM, instead on the DTM, and occluded areas were filled by combining information from several

source images. This product is essential in realistic 3D visualizations of textured terrain and landscape models, as in case of GEPSUS project.

Figure 8. DSM-based orthophoto (GSD 10cm) on Trento city center.

Figure 9. Difference between DTM-based (left) and DSM-based orthophotos (right) (Courtesy City of Linz,

Austria).

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3. Delivery

The delivery of Cluster 4 – Trento included: DSM-based orthophotos, GSD 10 cm, format GeoTIFF

Raw 3D point cloud with RGB information, density up to 100 points/m2 , format LAS + RGB

DSM/DTM with grid 2 m, format GeoTIFF.

The data were delivered in 3150 tiles with size 200m x 200m.

The reference system is UTM/ETRF2000 Zone 32N and ellipsoid heights.

4. Installation and interfacing with GEPSUS

The cluster “Trento” includes georeferenced products in universally standard formats (GeoTIFF, LAS) supported by the majority of commercial data management software in the geomatic community.

In case of GeoTIFF, today almost all commercial and open-source Geographic Information Systems (GIS), Image Processors (IP) and Computer Aided Design (CAD) software solutions can read the GeoTIFF files and

locate them into correct geographic position. Few examples of software packages are: ESRI Suite, ERDAS Imagine, ENVI, GlobalMapper, MapInfo, QGIS, GRASS, GDAL, etc.

In case of LAS format, it is the format recommended and used by companies dealing with laser scanning

observations, and in general 3D point clouds, both from air and terrain platforms. Examples of software supporting LAS format are: TerraScan, FugroViewer, CloudCompare, ZetaLog LAS Viewer, ESRI ArcGIS,

LAStools and many more libraries are available. Appendix I gives examples of use of LAS and TIFF files in different software environments.

In order to interface TERRA data set (GeoTIFF and LAS formats) with GEPSUS software the following

preprocessing steps are required: Export DEM for selected area (which include terrain and buildings) in Arc ASCII Grid format *.asc. It

can be done with Global Mapper or similar software from formats allowed by Terra.

Preprocess *.asc file with GEPSUS preprocessor software which is a part of GEPSUS software.

5. Training and support

In agreement with Graphitech, a representative from Terra Messflug will meet Graphitech in Trento to

respond to any requests regarding the products delivered in Cluster Trento and, eventually, to help with the data installation.

Terra Messflug operators remain at disposal of GEPSUS team for any information about the data characteristics and their usability.

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Appendix I. Visualisation of point cloud data (*.las) and orthoimages / DSM (*.tif) using different software products - Sample data from Trento Project 2014

1. Visualisation of *.las Files

Software: Global Mapper v15.2

Drag&Drop las-File to Global Mapper – Make setting to define the coordinate system:

If many *.las are loaded then tick the box “Use Selected Projections for All Selected Files”.

Define settings for *.las visualisation:

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Use “Draw Mode” to define if e.g. colour or elevation values should be visualised.

Example of colour (left) and elevation (right) visualisation:

To change from colour to elevation value visualisation use “Overlay Control Center” => “Options…” =>

change “Draw Mode”. 3D-View possible when clicking on “3D”

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Software: Cloud Compare v2.5.3

Drag&Drop las-File to CloudCompare – Make setting to define the coordinate system:

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SOFTWARW: SAGA-GIS 2.0.8

To open *.las: Tab “Modules” => “Import/Export – LAS” => “Import LAS Files” and navigate to *.las:

The result looks like this:

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Use “Point cloud viewer” for 3D:

Software: LasTools

See home page: (http://www.lastools.com/)

http://www.lastools.com/

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The lasTools are stand-alone toolsets from working with LiDAR data. They can also be used for *.las files

derived from dense image matching. Example tool “lasview.exe”. This is a small tool for visualisation:

Run the lasview.exe tool => “browse…” to file you want to visualise => double-click the file => click “VIEW” => click “START” (in new window) => use mouse to navigate in the new window “just a little LAS viewer”.

To change from RGB colour to colourised elevation values: right click in the window “just a little LAS viewer” => “color by…” => select “height”

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Example tool “lastool.exe”. This tool provides several possibilities to view, and analyse LiDAR data (see

toolbox on the right of the screenshot). It can also be used *.las files derived from dense image matching.

Software: ArcMap 10.0 ( ArcGIS)

Start a new empty project and set the coordinate system of the Layer to Projected coordinate system to WGS84 –

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UTM32:

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It is also possible to just add data into an existing project. If the project is in another coordinate system, the

projection of the data has to be set separately.

For the import of the point cloud, the Toolbox 3D Analyst Tools needs to be active. The point can be imported into project using the tool “LAS to Multipoint”. After the import it is possible to calculate other

formats (raster, TIN, etc).

2. Visualisation of *.tif Files (Orthophoto or DSM)

Software: Global Mapper v15.2

Same as for *.las: Drag&Drop to Global Mapper:

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Software: ArcMap 10.0

Import Orthophotos: Start a new empty project:

To add the tiff-files (orthos or DSM), press the “Add data” button. In the dialog box “Add Data, choose “Connect to folder” (marked yellow on the screen shot below), and choose the folder where your data are

situated.

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For a quicker display of the data – allow ArcGIS to make pyramids:

The image is ready to use in ArcGIS. If the ArcGIS Layer has no spatial reference, you have to input this. Right click on the “Layer” and choose “Coordinate system” and the predefined UTM32N zone as shown

below:

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If you import the data into an already existing project, please check that no auto-stretching is applied to the

radiometry. For a true visualisation of the radiometry – the settings must be as below:

If more or less contrast is wanted for visualisations, it is possible to set it in the dialogue box above.

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The data as presented in ArcGis:

Importing DSM into ArcGis Importing the DSM into ArcMap follows the same procedure are for orthos. However, after import, there might be a need to change the visualisation. Right-click on the DSM-layer and choose “Properties…” in the

dropdown menu.

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Below the color palette “black to white” is displayed with the Values repeated as Description:

This is how the data then looks:

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Other visualisation options are for example Elevation#1 (shown below) or simple green to red scale (preset in for example “Condition Number”):

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For better recognition of the terrain, it is feasible to add a hillshade in the visualisation:

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OR as black and white with exaggeration of the height values in the hillshade:

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Software: QGIS 2.6.0 Drag&Drop the *.tif to QGIS and set the Coordinate system (if necessary):

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When importing the Ortho, the result looks like this:

When importing the DSM, the result looks like this:

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You can change colours by:

Software SAGA-GIS 2.0.8: To open Ortho-tif: click on “Modules” => “Import/Export Images”=> “Import Image” => navigate to *.tif and use th option “Enforce True Color”. When the import is finish click on the tab “Data” => double click the

imported file => say “new”. The result looks like this:

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To open DSM-tif: click on “Modules” => “Import/Export – GDAL/OGR” => “GDAL: Import raster” => navigate to DSm-tif. When the import is finish click on the tab “Data” => double click the imported file =>

say “new”. The result looks like this:

Documents

3D GIS DATA set GEPSUS-TERRA Manual: Description, Installation … · 2014. 12. 4. · 3D modelling and DSM/DTM generation For the generation of the dense 3D point cloud, an advanced