Problems with Raster calculations in ArcGIS 10.2.1

Question

Hi there,

I am hoping someone out there can help with this rather annoying issue.

A few years ago I created some GRID raster files in ArcGIS 9.3. However, I have recently needed to reuse them for a project.

Now, I can open and display these GRID raster files quite easily in the new ArcGIS, but the moment I try and use the raster calculator to do a simple subtraction between them, I end up with a very course resolution raster. Unfortunately, I do not have access to an older ArcGIS 9.3 license (or I would have just used that version), but I am hoping there is a work around for this?

Thanks!

curtvprice · Answer

the moment I try and use the raster calculator to do a simple subtraction between them, I end up with a very course resolution raster.

If you do not specify a cell size in the environment, the default for Subtract is to use the maximum cell size of the two raster inputs. You can change the environment (Geoprocessing/Environments, or using the Environments button on the Raster Calculator tool) to use the minimum cell size between the two rasters you are subtracting instead.

ShaunWalbridge · Answer

Rebecca,

There shouldn't be any differences in support for GRID files between releases, I suspect it's something else. Is the geoprocessing environment set up to change the cell size? It's also possible that the rasters differ in resolution, and there's some automatic conversion going on to get them to match up before doing the calculation. Could you post some more details on the rasters themselves?

If do you do think it's explicitly an issue with them being GRID files, try converting the files to GeoTIFF and perform the same analysis -- if the same problem occurs, we'll know it's in the calculation step and independent of the file format.

cheers,
Shaun