topic Re: Extracting raster values according to different classes in ArcGIS Spatial Analyst Questions

Extracting raster values according to different classes

DitlevReventlow — Wed, 01 Jul 2015 19:39:08 GMT

Hey everyone.

I have a raster dataset (bshl_112p_srf) that I want to split up according to the classes that I have defined.

These classes are defined as:

158-535

535,0000001-686

686,0000001-1473

I have tried to use raster calculator to do this but it doesn't work. To extract the first class I tried to type:

Con("bshl_112p_srf" <= 535,"bshl_112p_srf")

, however I get an error for this expression.

What do I do wrong? Also, how would you extract the middle class (where you both need to have a <= and >= ).

Would it be something like:

Con("bshl_112p_srf" >= 535,0000001 & <=686,"bshl_112p_srf")

Thank you!

best regards

Ditlev Reventlow

Re: Extracting raster values according to different classes

JayantaPoddar — Wed, 01 Jul 2015 19:47:49 GMT

Class 1 = Con("bshl_112p_srf" >= 158 & "bshl_112p_srf" <= 535, "bshl_112p_srf")

Class 2 = Con("bshl_112p_srf" > 535 & "bshl_112p_srf" <= 686, "bshl_112p_srf")

Class 3 = Con("bshl_112p_srf" > 686 & "bshl_112p_srf" <= 1473, "bshl_112p_srf")

Re: Extracting raster values according to different classes

IanMurray — Wed, 01 Jul 2015 19:50:36 GMT

I see nothing wrong with your first statement, works fine for me.

Your middle class would need to be

Con("bshl_112p_srf" >= 535,0000001 & "bshl_112p_srf" <=686,"bshl_112p_srf").

Are you wanting to split them into three seperate rasters or truly make a new raster with 3 classes in it for each range with the same value? If so you might want to check out the Reclassify Tool.

ArcGIS Desktop

Re: Extracting raster values according to different classes

DitlevReventlow — Wed, 01 Jul 2015 19:51:23 GMT

Great thanks!

Re: Extracting raster values according to different classes

DitlevReventlow — Wed, 01 Jul 2015 20:35:34 GMT

Thanks for mentioning the reclassify tool. I had not tried to use it yet. I don't think I need it in this case though. It is probably more usefull for me to have 3 individual rasters.

Re: Extracting raster values according to different classes

DitlevReventlow — Wed, 01 Jul 2015 20:49:09 GMT

I tried to copy your statements but I get error 000539 error running expression rcexec().

What could the reason for this be?

Re: Extracting raster values according to different classes

JayantaPoddar — Thu, 02 Jul 2015 07:38:17 GMT

You need to copy the Con() statement only. Try selecting the layers from Layers and Variables in Raster Calculator dialog box. One expression for each output raster.

Re: Extracting raster values according to different classes

DitlevReventlow — Thu, 02 Jul 2015 08:06:30 GMT

I typed in raster calculator with those variable and expressions:

Con("bshl_112p_srf" >= 158,0000001 & "bshl_112p_srf" <= 535,"bshl_112p_srf")

It works now, but the output raster is first of all still covering the whole input original raster (not only the interval mentioned) and also the values are just termed 1. So all values have been reclassify to class 1, even though they were not inside the interval.

I would like to keep the original values (e.g. 535 instead of the new class 1) and only extract the values that are inside the interval. How can this be done?

Re: Extracting raster values according to different classes

JayantaPoddar — Thu, 02 Jul 2015 09:17:11 GMT

Ditlev,

use this expression

Con("bshl_112p_srf" >= 158 & "bshl_112p_srf" <= 535, "bshl_112p_srf", 0)

Also in Environment Settings > Raster Storage. Define the value of No Data as 0 (zero)

Re: Extracting raster values according to different classes

DitlevReventlow — Thu, 02 Jul 2015 11:20:18 GMT

I still get the same error message

I type this:

Con("bshl_112p_srf" >= 158 & "bshl_112p_srf" <= 535,"bshl_112p_srf",0)

And I have changed the nodata to 0.

Re: Extracting raster values according to different classes

JayantaPoddar — Thu, 02 Jul 2015 11:28:22 GMT

Move the location of the input/output rasters to shorter path (e.g. D:\Raster_Data).

Try enclosing the whole expression inside Float().

Float (Con("bshl_112p_srf" >= 158 & "bshl_112p_srf" <= 535,"bshl_112p_srf",0)).

Don't copy-paste from here. Select the Raster layers and Operations from the Raster Calculator dialog-box.

Re: Extracting raster values according to different classes

DitlevReventlow — Thu, 02 Jul 2015 12:15:23 GMT

Everything is typed in directly in raster calculator.

I tried to move it to a shorter path and added float(),

Float(Con("bshl_112p_srf" >= 158 & "bshl_112p_srf" <= 535,"bshl_112p_srf",0))

still the same error message.

If i type for instance:

Con("bshl_112p_srf" ==510 ,"bshl_112p_srf")

then this works with no problem. So the problem should be related to the <= and >=.

Re: Extracting raster values according to different classes

JayantaPoddar — Thu, 02 Jul 2015 12:24:19 GMT

An additional parenthesis when using &.

Class 1 = Con(("bshl_112p_srf" >= 158) & ("bshl_112p_srf" <= 535), "bshl_112p_srf")

Class 2 = Con(("bshl_112p_srf" > 535) & ("bshl_112p_srf" <= 686), "bshl_112p_srf")

Class 3 = Con(("bshl_112p_srf" > 686) & ("bshl_112p_srf" <= 1473), "bshl_112p_srf")

Hope this will work

Re: Extracting raster values according to different classes

DanPatterson_Retired — Thu, 02 Jul 2015 12:27:39 GMT

For your immediate concern... you should not be working in folders that contain a space...

In the future, you might want to look at Extract by Attributes—Help | ArcGIS for Desktop

since you have the spatial analyst. This will produce simpler approach and can be easily be put in a loop

Re: Extracting raster values according to different classes

DitlevReventlow — Thu, 02 Jul 2015 12:31:48 GMT

It works, thank you so much!!! Very gratefull!

Re: Extracting raster values according to different classes

DitlevReventlow — Thu, 02 Jul 2015 12:33:36 GMT

Okay I have done all my modelling working in this folder. What could the effects of it be?