why won't raster calculator work?

CathyReidy_Liermann

Hi all,

I'm trying to use Map Algebra/Raster Calculator on some tiff files, all of which are identical in properties but for cell values.  I keep getting an unidentified, unexpected error.  Am I wrong and tiff files don't work in raster calculator?  I converted 2 of them to GRID and tried a simple operation and no luck.  I tried an operation on just one, to make sure it really is the files themselves and not my expression.  Any ideas?  What do I need to do to make them work?  They're currently tiff continuous 32-bit floating point rasters.

Thank you!

curtvprice

Hi all,

I'm trying to use Map Algebra/Raster Calculator on some tiff files, all of which are identical in properties but for cell values.  I keep getting an unidentified, unexpected error.  Am I wrong and tiff files don't work in raster calculator?  I converted 2 of them to GRID and tried a simple operation and no luck. 

TIFF files work best when the values are limited to 8 bits (0-255). Beyond that bit range sometimes different software treats the values slightly differently which can lead to value conversion issues. I recommend examining the grids and see what the values in the grid version of the files are -- look at the raster statistics, and the raster table (if integer) and also maybe poke at the grids with the identify tool. Hopefully that will help figure out what's going on.

Arc 9.3.1 converts the TIFFs to grids behind the scenes before any map algebra is run. The behind the scenes conversion (using defaults) may be failing for some reason.

The second issue is georeferencing and coordinate systems this are sometimes specified slightly differently by different TIFF generating software. Since you say the TIFFs are identical except for the values, it sounds like this is less likely to be your issue.