topic con function use in the raster calculator in ArcGIS Spatial Analyst Questions

con function use in the raster calculator

MikeStrager — Fri, 21 Jan 2011 03:32:49 GMT

Ok, I am trying to use the con function in ArcGIS 10 raster calculator on a grid called "slopeperc" which is a floating point grid.

I want to change all values in "slopeperc" that are < 20 to 0 and if > 60 I want them to be 1. All other values should be subject to the equation ("slopeperc" -20) / 40. My resulting grid should be something that ranges from 0 to 1.

Thanks for your help!

Oh, this is what I have tried but can't figure out why I get an ERROR 000539 message and an output raster with nothing added to my table of contents.

Con("slopeperc" < 20, 0, con("slopeperc" > 60, 1, "slopeperc" - 20 / 40))

Re: con function use in the raster calculator

DanPatterson_Retired — Fri, 21 Jan 2011 10:24:15 GMT

try
Con("slopeperc" < 20, 0, con("slopeperc" > 60, 1, ("slopeperc" - 20) / 40.0))
given what you posted that you wanted and to avoid integer division

Re: con function use in the raster calculator

MikeStrager — Fri, 21 Jan 2011 12:53:50 GMT

Sorry, that still didn't work. I guess any insight on how to do a con inside another con would be helpful. I see the examples in Help but still can't get it right. Argh!

Re: con function use in the raster calculator

DanPatterson_Retired — Fri, 21 Jan 2011 14:00:20 GMT

well we both missed the glitch...Con != con
as an example
Con("grid1" < 2, 0, Con("grid1" < 3, 1, ("grid1" - 1) / 4.0)) worked for me with my sample expression
Con("grid1" < 2, 0, con("grid1" < 3, 1, ("grid1" - 1) / 4.0)) failed

In 10, one needs to be aware that expressions are case sensitive as well as space sensitive

Re: con function use in the raster calculator

MikeStrager — Fri, 21 Jan 2011 16:49:09 GMT

Yes, that was it!

The Con function needs to be capitalized even when nested in another Con for ArcGIS 10 raster calculator.

Thanks again.

Re: con function use in the raster calculator

DianeMcConnaughey — Wed, 30 Nov 2011 20:38:19 GMT

Also having problems with CON in raster calculator. The quotes and percent signs seem to get added when I drag a lyer listed above the expression. Could it be the "dot" syntax
CON("%hor_vis_rg%".count >= 23, 1)

So then I tried the CON function instead of Raster Calculator, with the SQL expression "Count" >= 310, and got the same Error.

Re: con function use in the raster calculator

DanPatterson_Retired — Thu, 01 Dec 2011 13:59:10 GMT

CON should be Con in 10
don't know about the % stuff and dot notation isn't supported as far as I know in 10

Re: con function use in the raster calculator

curtvprice — Fri, 02 Dec 2011 17:29:16 GMT

CON should be Con in 10
don't know about the % stuff and dot notation isn't supported as far as I know in 10

Yes, indeed, the new 10.0 Python map algebra does not support the "grid.item" notation (which has always been problematic for parsing expressions back to good-old GRID). The new way to do it is to use the [URL=http://help.arcgis.com/en/arcgisdesktop/10.0/help/009z/009z000000sn000000.htm]Lookup[/URL] tool:

Con(Lookup("%hor_vis_rg%","COUNT") >= 23, 1)

I believe "%" is model element notation -- like Diane is using the Map Algebra tool inside ModelBuilder, and "hor_vis_rg" is a data element inside the model.