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con function use in the raster calculator

MikeStrager

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))

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DanPatterson_Retired

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

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DanPatterson_Retired

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

MikeStrager

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!

DanPatterson_Retired

MikeStrager

Yes, that was it!

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

Thanks again.

DianeMcConnaughey

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.

DanPatterson_Retired

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

curtvprice

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.

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