topic Re: simple addition in raster calculator with incorrect sums in ArcGIS Spatial Analyst Questions

simple addition in raster calculator with incorrect sums

KyleAntonelis — Thu, 14 Mar 2013 05:17:32 GMT

Hello: I am building a simple linear additive model. I've got three reclassed rasters. Each of them include only the values 0,1,2,3,4,5,6.

When I use the raster calculator to add them, I get what looks to be a raster with correct values for cells from 1 - 18. However, when I run a quick QC on the output, I see that in many points the cell value is not equal to the sum of the cell values from the three original rasters.

Example: Point X
'tix' cell value = 6
'var' cell value = 6
'bathy' cell value = 5
OUTPUT Raster cell = 18

Any advice would be greatly appreciated.
Cheers

Re: simple addition in raster calculator with incorrect sums

Robert_LeClair — Thu, 14 Mar 2013 13:15:37 GMT

Kyle - are your cell sizes in the 3 rasters the same and what is the resampling parameter you're using in the Environment Settings?

Regards,

Robert LeClair
Esri-Denver

Re: simple addition in raster calculator with incorrect sums

KyleAntonelis — Thu, 14 Mar 2013 21:48:20 GMT

Robert: The cell size for all 3 rasters is 30x30 meters. But I have not gone into the Environment Settings at all. Sounds like that may be where I can fix this?
-Kyle

Re: simple addition in raster calculator with incorrect sums

KyleAntonelis — Fri, 15 Mar 2013 14:34:02 GMT

The problem was in the 'Processing Extent'. I set the extent to the base layer (bathy) and set the 'Snap Raster' to 'bathy' as well. This solved the problem. Thanks.