topic Re: Problem with Extraction by Attributes Output in ArcGIS Spatial Analyst Questions

Problem with Extraction by Attributes Output

steveSuperczynski — Mon, 18 Jul 2011 16:44:53 GMT

Has anyone else experienced an issue with output from the extraction tool in Spatial Analyst? I am trying to extract unwanted values from a raster and the result always comes up as a raster full of zeros. The odd thing is that I can select those values by the attributes but extracting them using SA will not work.

-Steve

Re: Problem with Extraction by Attributes Output

DanPatterson_Retired — Mon, 18 Jul 2011 16:51:17 GMT

ExtractByAttributes does not remove unwanted values from a raster. Can you describe the exact procedure you are using (ie which tool or raster calculator syntax)?

Re: Problem with Extraction by Attributes Output

steveSuperczynski — Mon, 18 Jul 2011 17:07:37 GMT

What I have is a large number of rasters that I want to average together. In order to do so I need to remove the missing values (-9999) and zeros from the raster. I was trying to use the extract by attributes to extract all values in the raster which are not "-9999" and "0" and save them to a new raster which I can use in the averaging process.

Or the SQL version "values <> -9999 and values <> 0"

This statement works great at selecting pixels via the attribute table which means it should work with the extraction by attributes tool as well I would think. However I'm positive the statement is not at fault because doing a simple clause wherein I try to extract all values greater than zero produces the same output.

-Steve

Re: Problem with Extraction by Attributes Output

DanPatterson_Retired — Mon, 18 Jul 2011 20:36:49 GMT

SetNull("MyRaster", "MyRaster", "Value <= 0")
might work (version 10 syntax

Re: Problem with Extraction by Attributes Output

steveSuperczynski — Tue, 19 Jul 2011 17:25:44 GMT

That will work but I have negative values that I need to keep in the raster so getting rid of everything less than zero will not give the desired output.

I can get it to work with two SetNull commands in Model Builder however I was having trouble getting it to work in a script and thought the extraction tool would be easier (only to be wrong again!). I must admit though my knowledge of python and the arc10 command window are quite limited so it could be I am just messing something up there that could be easily remedied.

Thanks for the ideas,
Steve

Re: Problem with Extraction by Attributes Output

curtvprice — Tue, 19 Jul 2011 22:34:20 GMT

That will work but I have negative values that I need to keep in the raster so getting rid of everything less than zero will not give the desired output.

Arc 10:

SetNull("MyRaster", "MyRaster", "Value = 0 OR Value = -9999")

Arc 9.3 Single Output Map Algebra:

setnull(myraster eq 0 or myraster eq -9999,myraster)

Re: Problem with Extraction by Attributes Output

steveSuperczynski — Wed, 20 Jul 2011 13:05:50 GMT

Yep tried that already too... I don't know why but whatever I try does not seem to work properly. Using the SetNull command gives me strange output where none of the -9999 values are removed and only some of the 0 values are removed.

Re: Problem with Extraction by Attributes Output

curtvprice — Wed, 20 Jul 2011 14:27:44 GMT

You may be at the mercy of the format of ENVI's .tif file output, in which case the best solution is to convert to grid -- the only sure way to control bit depth, etc.

I highly recommend you take this to tech support. If the problem is on the ArcGIS side, this is the only way things like this get fixed.

Re: Problem with Extraction by Attributes Output

steveSuperczynski — Wed, 20 Jul 2011 19:23:10 GMT

Well these tiff images were converted from .hdf files using the MODIS Reprojection Tool (MRT). This has not caused any issues with ArcMap before. The extraction process works like a charm in 9.3 so I think there is def something up with how ArcGIS 10 is handling these .tif files. I have contacted ERSI support so we will see what they come back with.

Thanks,
Steve