topic Re: Raster Calculator trouble in ArcGIS Spatial Analyst Questions

Raster Calculator trouble

RolandoLopez1 — Tue, 15 Mar 2011 19:42:24 GMT

hello everyone, i dont know if anyone is familiarized with spatial analyst courses from ESRI but right now im trying to make some exersises that were made for arcgis 9.3 like making a raster from a selection (this is in the second chapter) ussing raster.field worked in earlier versions but now i dont know how to do it to get the same results as in the earlier version (i almost solved this by using the extract by atribute but not with the same results and the questioning continues... have someone tryied to make this excersices with the arcgis 10.?

Re: Raster Calculator trouble

TimothyHales — Wed, 16 Mar 2011 11:05:33 GMT

There are some slight syntax changes from 9.3 to 10. There is also the ability to carry out many of these processes with the Python window. Please give an example of the statement that is not working and I'd be glad to look at it.

Re: Raster Calculator trouble

PatrickTaurman — Wed, 16 Mar 2011 11:54:50 GMT

Dot Notation currently does not work in the new Raster Calculator or in Python. There is an enhancement request to bring this functionality back.

Patrick

Re: Raster Calculator trouble

RolandoLopez1 — Wed, 16 Mar 2011 13:30:05 GMT

in earlier versions you just write layer.attribute and then just with that you were able to create a raster based on that attribute only now this sintaxys gives trouble, for example ersoil.Soil_Ph to calculate only that field or if i want to add for example ersoil.Soil_Ph + ersoil.Soil_Ph2 what would be the sintaxys. thnx 4 the answers!

Re: Raster Calculator trouble

PatrickTaurman — Wed, 16 Mar 2011 14:11:42 GMT

I thought I had put this in my post, but looks like I forgot. You can use the Lookup tool, to create a new raster based on a field, and then use that in the Raster Calculator.

Patrick

Re: Raster Calculator trouble

RolandoLopez1 — Wed, 16 Mar 2011 15:02:58 GMT

Thnx Patrick! ok ive tried that two, but what happens if i have to make a add opperation like the one i mentioned earlier e. soil.Ph + vegetation.Ph can i do this on the calculator or do i have to make more steps?

Re: Raster Calculator trouble

PatrickTaurman — Wed, 16 Mar 2011 15:11:48 GMT

You need to run Lookup on soil and vegetation using the Ph field, then you can add the two new rasters created from the tool together.

Re: Raster Calculator trouble

RolandoLopez1 — Thu, 17 Mar 2011 14:06:25 GMT

thnx for your answers ive been playing with this and discover alternative ways, unfortunately the calculator is not as powerfull as before you have to ake some steps more to reach the same results as before. 😞

Re: Raster Calculator trouble

GregYetman — Fri, 08 Apr 2011 17:48:16 GMT

I used the . notation in 9.3 and couldn't figure out why it didn't work at 10! Thanks for clarifying this.

The Lookup tool only supports integer output. Does anyone have a workaround for floating point data in another field?

Re: Raster Calculator trouble

SteveLynch — Fri, 08 Apr 2011 19:59:11 GMT

Greg

Only integer rasters have other fields. A floating point raster does not have any other fields.

Steve

Re: Raster Calculator trouble

EricRice — Mon, 11 Apr 2011 19:49:59 GMT

The Lookup tool only supports integer output. Does anyone have a workaround for floating point data in another field?

Greg,
The Lookup tool is not limited to integer output. I just created a field of type Float, and populated it with floating point values. When I use this field in the Lookup tool, I get a floating point raster as output. Is it possible you have floating point values stored in a text field?

The documentation for the Lookup tool does state, "The output will always be of integer type". This is wrong, and I've notified the appropriate team so they can change that sentence in the doc.

Regards,
Eric

Re: Raster Calculator trouble

NishaKrishnan — Tue, 26 Mar 2013 20:11:27 GMT

I, too, have a similar problem as stated in this thread. I tried using the lookup function on my raster, but it keeps erroring out and gives me the following error:[ATTACH=CONFIG]22969[/ATTACH]

I would ideally like to export the MinMax field (the last field) into its own separate raster or is there an easier way to use the minmax field in calculations with other floating point rasters?

Thanks!

Re: Lookup tool fails

curtvprice — Wed, 27 Mar 2013 02:28:13 GMT

I, too, have a similar problem as stated in this thread. I tried using the lookup function on my raster

Some ideas:

- Set the workspace and default workspace to the same location, copy your raster to that same workspace, and try running Lookup again. This is generally best practice when working with raster tools, as the conversion of temporary to permanent rasters only requires a rename, not copying the whole raster.

- It's also just generally safer to have the Lookup operate within the same workspace, as there are joins at work.

- Make sure your environment (cell size, mask, or extent) aren't interfering with your processing.

Re: Raster Calculator trouble

curtvprice — Sun, 12 Dec 2021 01:58:07 GMT

what happens if i have to make a add opperation like the one i mentioned earlier e. soil.Ph + vegetation.Ph can i do this on the calculator or do i have to make more steps?

I didn't see a direct answer to this in the thread, so here's how you do that in one step using the Raster Calculator tool in ArcMap:
("soil" and "vegetation" are two raster layers, both with a raster table field "ph")

Lookup("soil","ph") + Lookup("vegetation","ph")

In arcpy scripting, you may have to access the rasters by pathname. Here's how that works:

from arcpy.sa import *
arcpy.env.workspace = "D:/myfolder" 
# "soil.img" and "vegetation.img" are in this folder
# the Raster function is used to convert the path strings to a raster object
phsum = Lookup(Raster("soil.img"),"Ph") + Lookup(Raster("vegetation.img"),"ph")
phsum.save("phgrid") # save to Esri grid D:\myfolder\phgrid

Re: Raster Calculator trouble

DianeMcConnaughey — Tue, 25 Jun 2013 14:19:33 GMT

"Lookup" usually fails in raster calculator, even when I run the same process from "results". Here is the process I'm trying to run in raster calculator. If it worked, I'd like to string together the 10 rasters I am working with.
lookup("veg2_p34_Weiser","veggie_minus_Tall")
Can I use lookup to mosaic rasters? The reason I do not want to use mosaic, is that cannot specify the item to use in mosaic ( or at least I have not found the sytax), and I'm getting frustrated having to create new GRIDs with the value from the item I want to use

Re: Raster Calculator trouble

curtvprice — Sun, 12 Dec 2021 01:58:10 GMT

"Lookup" usually fails in raster calculator

I hope this question is not unwarranted, but are you always capitalizing the name of the "Lookup" tool? Tool names are case-sensitive in ArcGIS 10's Raster Calculator and arcpy.

If you create a raster with the Create Raster Dataset tool, you can use Mosaic in arcpy map algebra with Lookup like this:

Mosaic([Lookup("grid1","FIELD1"), Lookup("grid2","FIELD2")], "mergeraster")

Re: Raster Calculator trouble

DianeMcConnaughey — Wed, 26 Jun 2013 13:43:53 GMT

I've completed what I need to do for the time being, but will try your suggestion when things slow down, it would definitely be more efficient than the step-by-step approach I ended up using. I was trying these operations both in Windows 10.0 SP4 with data on the network and in windows 10.1 (Sp?) with data on the local hard drive. The 10.1 usually worked, while 10.0 usually failed. 10.0 also failed to load tables into a newly created FGDB table - both directly from GRIDs and from ascii output from those GRIDs - it just did not "see" them. 10.1 worked. In raster calculator it would be nice to be able to chose the "Lookup" function (and other functions) so that "case" is not an issue, as well as being able to select the "item" to use in the lookup.

Re: Raster Calculator trouble

curtvprice — Sun, 12 Dec 2021 01:58:12 GMT

. In raster calculator it would be nice to be able to chose the "Lookup" function (and other functions) so that "case" is not an issue, as well as being able to select the "item" to use in the lookup.

You may want to try just entering map algebra in the python window in ArcMap instead of Raster Calculator. This supports fixing capitalization etc. For example, try this in the ArcMap Python window with some raster layers in your map

>>> from arcpy.sa import *
>>> ras = Con

You'll see popups that guide you through entering the map algebra.

Desktop 10.1 Help: Comparing Map Algebra between ArcGIS 9.x and 10