Problems merging DEMs or other raster datasets? Clipping Raster dataset to vector line?

Question

I have two DEMs that I am going create a hillshade from, and ultimately want one hillshade clipped to a county boundary. I am running into a couple problems, though.

When I try to merge the two hillshades created from the DEMs, ArcMap crashes. When I try to merge the two DEMs, ArcMap crashes. I am assuming that if I managed to get the DEMs merged, the hillshade created would cause ArcMap to crash, too.

I am using the PLTS Merge Raster Datasets tool, because for some reason the Spatial Analyst tool Raster Calculator does not appear as selectable.

Once I am able to do this and get a hillshade of the two DEMs, is there a specific function for using the county line (which is a vector fc) to clip the raster data set to?

Answer 1

I've never used the PLTS tools, and the help doesn't really give much info on how the Merge Raster Datasets works, but the Mosaic to New Raster geoprocessing tool, in the Data Management Toolbox under Raster Dataset, should work fine, and doesn't require an ArcInfo license or Spatial Analyst.

To clip your resulting mosaic without Spatial Analyst, use the Clip geoprocessing tool, also in Data Management under Raster Processing, and use the county line feature as the Output Extent. If you have the county feature selected and enable the "Use Input Features for Clipping Geometery" option, it will clip to the actual border. If you don't select the feature, it will clip the raster to the bounding box of the feature.

Answer 2

Actually, you can find an alternative in GDAL FOSS software package. Assuming that raster files are in a format GDAL can read, you could process them using following steps:

1. create virtual raster using gdalbuildvrt util, by building virtual raster you can save on disk space and processing time
2. use util gdalwrap to cut raster using prepared cutline in any OGR supported format

For more information you can check this page http://linfiniti.com/2009/09/clipping-rasters-with-gdal-using-polygons/, also you can find GDAL/OGR tools and other FOSS for windows operating system in OSGEO4w binary distribution.

Answer 3

To clip your hillshade, use Extract By Mask (assuming you have Spatial Analyst) and specify your county feature class as the "feature mask data."

Answer 4

Concerning crashes... This may or may not be germane to your specific problem. Whenever it appears that I am doing things right and ArcGIS is inexplicably crashing, my first two actions are:

• make sure I am logged in as Administrator on the computer.
• export my data from within ArcGIS (basically just resaving it).

Of course, double check to be sure your Spatial Analyst and any other workflow-related extensions are turned on. Note: I am rolling full ArcInfo licenses, and do not know the behavior in ArcView or ArcEditor.

Answer 5

One word: GlobalMapper Your raster processing nightmares will be over, all for a whopping $350. What you are trying to accomplish is cake in GM.

EDIT:

Here is how you clip a raster to a vector polygon in GlobalMapper (ver. 13.2 used here):

1. Load your raster and vector polygon into GlobalMapper

2. Select the polygon using the Feature Info tool, then turn it off in the Overlay Control Center (otherwise it will be included in your export):

   

3. Go to either File|Raster/Image format or File|Export Elevation Grid format (I'm going to do Raster/Image)

4. Select your export format from the dropdown. Next on the Export Option, on the Export Bounds tab, select Crop to Selected Area Feature(s):

   

5. Continue with the export, you will get a raster with the extent of your clip polygon.