Raster Calculator - Mathematical Operation

Discussion created by dwightlanier on Feb 1, 2011
Latest reply on Feb 2, 2011 by dwightlanier
Hi All,

I have several multiple observer viewsheds created in ERDAS and saved out as .img files.  I broke up the area to be covered into segments that overlap to reduce file size and make the viewsheds run, and need to add them all together to get one final surface that shows number of observers that can see each location.

After a reclass in ArcGIS the pixel values represent the number of observers that can see each location without the hidden, boundary, etc. classes that ERDAS encodes into the viewsheds.  If I use the indentify tool, the returned pixel value is the correct number.  The problem comes when trying to use raster calculator to add all of the rasters together.  Whether I add two of the files together, or all 5, the resulting values are not the simple 1 - 5 observers that I would expect to get.  Instead, where the two rasters do not overlap I get values in the 400s and 500s.  I tried multiplying the rasters by 1.0 to see if this would solve the problem, but it doesn't.

Is this a problem with the file format not being compatible?  I would think that a simple summation over each cell location would work fine.

Thanks for any suggestions and time.