topic Re: Raster extraction in ArcGIS Spatial Analyst Questions

Raster extraction

WesKing — Fri, 11 Jun 2010 22:52:43 GMT

ArcInfo v9.3.1 sp1
Having a DEM ranging from 2500 to 3500 I would like to create 2 separate DEMs; 1 ranging from 2500 to 3000 and the other from 3001 to 3500. Which tool would work best to create these DEMs using statements such as [DEM] <= 3000and [DEM] >= 3001. I don't want a conditional return like I get in Raster Calculator (maybe I'm doing doing it wrong though). I want the true values returned with all other pixels not satisfying the statement to be NoData.

Thanks in advance.
Wes

Re: Raster extraction

DanPatterson_Retired — Sat, 12 Jun 2010 09:29:52 GMT

setnull
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?topicname=setting_values_to_nodata:setnull

Re: Raster extraction

WesKing — Tue, 15 Jun 2010 18:16:19 GMT

Dan/William,
Thanks for the advice.

Dan, I don't think SetNull will work because it requires an integer type for the input conditional raster.

William, Sorry but can I ask for some clarification on your advice? Set the extent where?

Thanks,
Wes

Re: Raster extraction

JeffreyEvans — Tue, 15 Jun 2010 19:51:10 GMT

You are not correct in your assertion that SETNULL requires an integer raster. If I understand your post, what you want to do is as simple as the following raster calculator statement:

SETNULL([dem] >= 3001, [dem])
SETNULL([dem] <= 3000, [dem])

You can also define an embedded range (i.e. 2800-3200) using SETNULL.

SETNULL([dem] >= 2800 & [dem] <= 3200, [dem])

Re: Raster extraction

WesKing — Tue, 15 Jun 2010 21:39:15 GMT

Jeffrey,
Thanks for the input...worked great! So you're right about not requiring an integer raster. See the attached though, using Set Null in Conditional tools states that an integer raster is required. Either way it worked and thank you very much. I'm still learning many of these tools and the syntax involved. Without you guys I would just sit in the fetal position rocking back-and-forth, with an occasional scream from head pain.

William, I'm still interested in hearing a little more detail on your post (if you don't mind).

Wes

Re: Raster extraction

DanPatterson_Retired — Tue, 15 Jun 2010 22:30:44 GMT

to all, I was reading the 10 help files
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z00000007000000.htm
which indicates

The input conditional raster does not affect whether the output data type is integer or floating point. If the input false raster (or constant value) contains floating-point values, the output raster will be floating point. If it contains all integer values, the output will be an integer raster.

which I didn't compare to the 9.3.x help files, if that clarifies, with Bill's cavaet about range issues.

Re: Raster extraction

WesKing — Tue, 15 Jun 2010 23:00:45 GMT

Thanks again to both of you.

And yes you're right about being meticulous with the range values. I had noticed I written it incorrectly in my first post, even though I wasn't going to be using those exact numbers for my ranges (sloppiness in my posting). I just finished running Raster Calculator a couple times because I hadn't used the correct operator (> as opposed to >=) to make sure I covered all values.

I'm sure I'll be back soon.

Wes