Converting Lidar Data

7/29/2019 Converting Lidar Data

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Converting Lidar Data to Shapefile and RasterFile Format for Analysis and Viewing

1. Create a File Based GeodatabaseOpen ArcCatolog and right click under contents and click New and FileGeodatabase where you want to create the gdb. Name it something thatmakes sense


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2. Create a Terrain Dataset

First create a new Feature Dataset to store the terrain.In ArcCatolog right click in the geodatabase which you just made, and click onNew and Feature Dataset


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Type in the name of the Feature Dataset and click next

Next click New and Terrain.


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Click on Projected Coordinate Systems and then navigate to UTM andNAD 1983 then select Nad 1983 Zone 17N and then click next. This projectioninformation input here is from the metadata that came with the data.


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Next define the Vertical Coordinate System by selecting NAVD1988 as shownbelow and click next. This information is also from the metadata.


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Leave the XY Tolerance at the default, then click finish.

3. Create a Point Information File


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Fill out the Point File Information dialogue box

Input select all xyzi files needed for processing

Output Feature Class the name of the geodatabase orshapefile for output

Input File Format xyzi

Input Coordinate System NAD 1983 UTM Zone 17

The Point File Information tool will generate an index for the xyzi files as well as

statistical information for point spacing for each asci file. The z max and minvalues for each ascii file which were converted in point number 4 below, Convertthe xyzi files to a feature class.


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The result is an index file that has attribute information about each tile.

By right clicking on the attribute table you can then click on statistics and getinformation about any field. In this case we want to know the statistics aboutPt_Spacing to get a ballpark idea about what size the average point spacing ofthe points are.


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These are the stats of the Pt_Spacing field. You can see below the Max numberis over 51.

Next select all records except the value over 51 and run the statistics again. Thisnumber should be rounded up to the whole number when it is a decimal point .This number will be used in generation of the raster image.

Now we will sort the field using the descending option to put all large values atthe top


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Here is the sorted table. Notice several records are well above 3. We will nowselect all records below 3.

Now when we do a statistics on the field the result looks like this. The mean is .8This value will be used on page 13 for generating the Terrain. We will round 0.8to the first whole number which is 1 and use this in the generation of a rasterimage below.


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4. Convert Lidar ASCII Files to a Point Feature Class

Convert the xyzi files to a 3DFeatureClass.

In ArcToolBox under3D Analyst Toolsclick Conversion,From File andASCII 3D to Feature Class


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Fill out the dialogue box with the following information where

Input Files can be one or more xyzi files

Input File Format choose xyzi

Output Feature Class name of a Shapefile or Feature Class

Output Feature Class Type choose Multipoint

Input Coordinate System Nad 1983 UTM Zone 17

Average Point Spacing 0.3 as per metadata


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Output will look similar to this point feature class

For the Toronto Lidar dataset both First Pulse, all shots and extracted features aswell as Last Pulse, extracted features and ground will have to be processed inthe same way.


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5. Create a Terrain

Open ArcCatalog. Go to the Feature Dataset created above and double clickit Then right click in the background and click New and then Terrain

Choose a terrain name that makes sense. Here we will use Terrain_First.Approximate PointSpacing can be determined by using statistics as shownabove in point 3. Create a Point Information File. We will use 0.8 here.Then clicknext.


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Pyramid Type select Z Tolerance

Create Pyramid Properties. Click Calculate Pyramid Properties.

Click next and then finish and your Terrain will be processed


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6. Generate a Raster Image from the lidar point files.

Go to Conversion Tools,To Raster, Point to Raster


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Fill out the dialogue box as follows and then click ok.

Input Features point file to generate raster from

Value Field Shape.Z which contains elevation data

Output Raster Dataset name of raster

Cell Assignment Type MINIMUM see note below

Cellsize 4 which is about 4 times larger than thestatistics number from above when rounded to a full number

NOTE:From the ESRI help:

Set Cell assignment type to eitherMIN orMEAN. MIN will bias output heights tolocal lows, while MEAN is more of a general purpose option. To produce a firstreturn surface, or DSM, use the first return lidar points with the MAX option of the

tool since you want to bias the output to local highs


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7. Create an Intensity Image

First a new feature class has to be created from the xyzi data using the ivalue (intensity). As above in point 4 go to ASCII 3D to Feature Class

Input xyzi file(s)

Input file format XYZI

Output Feature Class put in geodatabase with appropriatename

Output Feature Class Type Point Input Coordinate System NAD 1983 UTM Zone 17N


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Create a raster image from the point data to be used to view data in arcmap asyou did in point 6 above. Go to Conversion Tools, To Raster, Point to Raster

Input Features ground_intense

Value Field Intensity

Output Raster Dataset ground_intense_rast stored in geodatabase

Cell Assignment type MEAN

Priority Field NONE

Cellsize 1

First Pulse, All Shots and Extracted Features and Last Pulse, Ground andExtracted Features can all be processed and used in ArcMap to view that looksimilar to aerial photos.

Each of these can be overlayed with the others to create an intensity image inArcMAP.

Documents

Converting Lidar Data