topic Re: How to multiply two layers base on particular fields? in ArcGIS Spatial Analyst Questions

How to multiply two layers based on particular fields?

JamalNUMAN — Sat, 26 May 2012 18:56:21 GMT

How to multiply two layers based on particular fields?
In the screenshot below, I wanted the first raster based on the field named ???I_factor??? with the second raster based on the field named ???value??? but couldn???t know the correct syntax to perform this process!
What might be the correct syntax?

[ATTACH=CONFIG]14673[/ATTACH]

Thank you for the help,
Best
Jamal

Re: How to multiply two layers base on particular fields?

TimothyHales — Tue, 29 May 2012 19:15:09 GMT

You should be able to do this with the Lookup function similar to one of your other forum posts:What is wrong with this syntax when using the ???raster calculator????.

"P_rec" * Lookup("I_rec","I_factor")

Re: How to multiply two layers base on particular fields?

JamalNUMAN — Fri, 01 Jun 2012 07:43:44 GMT

You should be able to do this with the Lookup function similar to one of your other forum posts:What is wrong with this syntax when using the �??raster calculator�?�?.

"P_rec" * Lookup("I_rec","I_factor")

Many thanks for the help Timothy. The syntax you have provided solved my issue.

[ATTACH=CONFIG]14850[/ATTACH]

Re: How to multiply two layers base on particular fields?

JamalNUMAN — Sun, 05 Apr 2020 08:37:28 GMT

Is there a way to use the “times” tool in order to multiply two rasters based on particular fields?

Re: How to multiply two layers base on particular fields?

NawajishNoman — Sun, 05 Apr 2020 17:51:40 GMT

Hi Jamal,

You can use the Lookup tool to create a new raster by looking up values found in another field in the table of the input raster.

You can create a model or you can write a map algebra expression as follows to solve your problem.

This map algebra expression does 3 things in one shot

1. It creates a raster using the value from P_Value field from P_map raster - let's call it P_Value_Raster

2. It creates a raster using the value from I_Factor field from I_map raster - let's call it I_Factor_Raster

3. Finally it multiplies P_Value_Raster with I_Factor_Raster to create the final output times_ P_I raster object

Since the expression is executed in one shot, you don't see the outputs from step 1 and 2. You get the final output times_ P_I .

However, the output from a map algebra expression is temporary, so, don't forget to save your output by calling the Save method.

Thanks

Noman

Re: How to multiply two layers base on particular fields?

JamalNUMAN — Mon, 06 Apr 2020 06:44:51 GMT

Thanks Nawajish.

It appears that using the “raster calculator” tool is much efficient in this case

Lookup("%P_Rank%","P_Rank") * Lookup("%I_map%", "I_Factor")

Re: How to multiply two layers base on particular fields?

NawajishNoman — Mon, 06 Apr 2020 22:19:46 GMT

Hi Jamal,

I am glad that you find Raster Calculator more efficient for your workflow.

The Raster Calculator tool is designed to execute a map algebra expression in a model. It executes the same expression as you would do in Python Window or in a standalone Python script. However, it creates a persisted output like any other Geoprocessing tool.

From analytical and execution point of view, it works the same way like any map algebra expression, just a different user experience.

Please free free to use whatever suits your workflow. Please let me know if you see any real performance different between executing it from a Raster Calculator and from Python Window or in a standalone Python script.

I hope, you are enjoying the Lookup functionality which has been improved recently to make it efficient.

Thanks!

Noman