Converting Lidar Data to Shapefile and Raster File Format for Analysis and Viewing

Transcription

1 Converting Lidar Data to Shapefile and Raster File Format for Analysis and Viewing 1. Create a File Based Geodatabase Open ArcCatolog and right click under contents and click New and File Geodatabase where you want to create the gdb. Name it something that makes sense

2 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 on New and Feature Dataset

3 Type in the name of the Feature Dataset and click next

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

5 Next define the Vertical Coordinate System by selecting NAVD 1988 as shown below and click next. This information is also from the metadata.

6 Leave the XY Tolerance at the default, then click finish. 3. Create a Point Information File

7 Fill out the Point File Information dialogue box Input select all xyzi files needed for processing Output Feature Class the name of the geodatabase or shapefile 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 min values for each ascii file which were converted in point number 4 below, Convert the xyzi files to a feature class.

8 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 get information about any field. In this case we want to know the statistics about Pt_Spacing to get a ballpark idea about what size the average point spacing of the points are.

9 These are the stats of the Pt_Spacing field. You can see below the Max number is over 51. Next select all records except the value over 51 and run the statistics again. This number 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 at the top

10 Here is the sorted table. Notice several records are well above 3. We will now select all records below 3. Now when we do a statistics on the field the result looks like this. The mean is.8 This value will be used on page 13 for generating the Terrain. We will round 0.8 to the first whole number which is 1 and use this in the generation of a raster image below.

11 4. Convert Lidar ASCII Files to a Point Feature Class Convert the xyzi files to a 3D Feature Class. In ArcToolBox under 3D Analyst Tools click Conversion,From File and ASCII 3D to Feature Class

12 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

13 Output will look similar to this point feature class For the Toronto Lidar dataset both First Pulse, all shots and extracted features as well as Last Pulse, extracted features and ground will have to be processed in the same way.

14 5. Create a Terrain Open ArcCatalog. Go to the Feature Dataset created above and double click it 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 Point Spacing can be determined by using statistics as shown above in point 3. Create a Point Information File. We will use 0.8 here.then click next.

15 Pyramid Type select Z Tolerance Create Pyramid Properties. Click Calculate Pyramid Properties. Click next and then finish and your Terrain will be processed

16 6. Generate a Raster Image from the lidar point files. Go to Conversion Tools, To Raster, Point to Raster

17 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 the statistics number from above when rounded to a full number NOTE: From the ESRI help: Set Cell assignment type to either MIN or MEAN. MIN will bias output heights to local lows, while MEAN is more of a general purpose option. To produce a first return 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

18 7. Create an Intensity Image First a new feature class has to be created from the xyzi data using the i value (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 appropriate name Output Feature Class Type Point Input Coordinate System NAD 1983 UTM Zone 17N

19 Create a raster image from the point data to be used to view data in arcmap as you 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 and Extracted Features can all be processed and used in ArcMap to view that look similar to aerial photos. Each of these can be overlayed with the others to create an intensity image in ArcMAP.

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