topic Only extract values that are the same in two raster dataset in ArcGIS Spatial Analyst Questions

Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 12:47:57 GMT

Hey everyone.

I have two raster datasets with the same spatial resolution and extent. Both these datasets have values between 0 to 16.

How do I extract only the values that are the same in both datasets?

Thank you!

Best regards

Ditlev Reventlow

Re: Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 12:49:14 GMT

I mean where the cells in the two datasets have the same values.

Re: Only extract values that are the same in two raster dataset

JakeSkinner — Thu, 11 Jun 2015 13:11:32 GMT

Hi Ditlev,

You could use the Minus tool to subtract the two rasters. Then, perform an Extract Values by Attributes for values that equal 0. These represent the cells that have the same value.

Re: Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 13:12:34 GMT

I think I might have gotten it to work now, but I am not completely sure.

I have written the following in raster calculator:

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2012_e")

Does this look right?

I guess it is the same if I write:

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2001_e")

Am I right about this conclusion?

Re: Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 13:15:24 GMT

Great Thanks, do you think that my approach with raster calculators works as well?

Re: Only extract values that are the same in two raster dataset

DanPatterson_Retired — Thu, 11 Jun 2015 13:30:11 GMT

Although they are identical, I think what you mean, is if the order of the rasters was switched in the equality check, the values would remain the same where the values are equal in the different time periods, but they would assume a different value where they are not equal. So the question remains, what do you want to happen when the values are NOT equal

this == that then keep this OR that...doesn't matter
this != that then keep ???? or do something else
this == that, keep this, otherwise give it 0

Don't get hung up on the contents, focus on the logic

Re: Only extract values that are the same in two raster dataset

JakeSkinner — Thu, 11 Jun 2015 13:32:12 GMT

Yes, your Con statement appears to be correct.

Re: Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 15:10:14 GMT

Dan,

I meant what is written,

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2012_e")

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2001_e")

But I am also intested in what happens if you turn around the rasters in the equality check. I just tried to play around in raster calculator. As far as i could see all these 4 statements:

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2012_e")

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2001_e")

Con("bsh_lu_2001_e" == "bsh_lu_2012_e","bsh_lu_2012_e")

Con("bsh_lu_2001_e" == "bsh_lu_2012_e","bsh_lu_2001_e")

all yeld the same output raster.

I want the output raster to have no value where the two rasters differ. This is the case for all the 4 statements above as far as I can see(when I right click and select "identify" on a cell that doesn't have the same value, there is simply nothing stated) .

I am not completely sure what you mean in the three examples you have given.

Re: Only extract values that are the same in two raster dataset

DanPatterson_Retired — Thu, 11 Jun 2015 15:37:27 GMT

Con("bsh_lu_2001_e" == "bsh_lu_2012_e","bsh_lu_2001_e")

just leave the result the same if it isn't true

Con("bsh_lu_2001_e" == "bsh_lu_2012_e", "bsh_lu_2001_e", 0)

Con("bsh_lu_2012_e" == "bsh_lu_2001_e", "bsh_lu_2001_e", 0)

will set the value to " 0 " IF they aren't equal

Con statement help

Con statement how it works

That is what I was trying to get you to think about .... what to do if they weren't equal ...

Re: Only extract values that are the same in two raster dataset

DitlevReventlow — Thu, 11 Jun 2015 15:52:22 GMT

Dan,

Thank you for this. I don't want the "not-similar" data to be set to 0, I just want them not to be included in the output raster.Then I guess that it is fine to write:

Con("bsh_lu_2012_e" == "bsh_lu_2001_e","bsh_lu_2012_e")

Right? (just wanted to make sure because this is the statement I have used)

Re: Only extract values that are the same in two raster dataset

curtvprice — Sat, 13 Jun 2015 03:18:38 GMT

Yes, when you don't provide a "false expression" to Con, and the first argument resolves to false, the output cell value will be NoData.

Re: Only extract values that are the same in two raster dataset

DanPatterson_Retired — Sat, 13 Jun 2015 03:49:26 GMT

If you are doing this in the Raster Calculator explore your options

Con("x4" == "x2",5,"x4") F:\Test\x5... if x4 is equal to x2 give it a value of 5, otherwise keep x4's values

From the Results Window

Messages

Executing: RasterCalculator Con("x4" == "x2",5,"x4") F:\Test\x5

Start Time: Fri Jun 12 23:46:41 2015

Con(Raster(r"x4") == Raster(r"x2"),5,Raster(r"x4"))

Succeeded at Fri Jun 12 23:46:41 2015 (Elapsed Time: 0.11 seconds)

Note the addition of Raster around the input raster layer names

Re: Only extract values that are the same in two raster dataset

curtvprice — Sat, 27 Jun 2015 05:36:10 GMT

There's also the Diff tool.