topic Re: export raster as stretched value from model builder in ModelBuilder Questions

export raster as stretched value from model builder

jamiefinney — Tue, 24 Nov 2015 16:56:54 GMT

i'm trying to export a raster with its stretched values (0-255) and i can't figure out how to do it via the model builder.

normally this can be achieved by

right clicking the raster in the Table Of Contents

Data > Export Data...

Tick the "Use Renderer" box

how would i achieve this using the model builder?

Re: export raster as stretched value from model builder

DuncanHornby — Mon, 15 Feb 2016 16:00:32 GMT

The method you use from the GUI is not exposed in modelbuilder. You would have to calculate a new raster with the stretch.

Below are some notes I had written to myself:

You have a raster and you want to stretch the values into a different range. For example you have an elevation grid which ranges from 1 to 1000 but you want to stretch this into a grid ranging from 1 to 10. This is different to using the standard Reclassify tool as this would lump them into classes.

In a nutshell you convert you existing raster values to a proportion between 0 and 1 then alter the proportion value by a scalar.

In the example above we type the following into a raster calculator (remember to substitute the words with values):

(([EleGrid] - eleMin) / eleRange) * newRange ) + newMin

[EleGrid] = is the grid name, in this example assumed to be an elevation grid
eleMin = is the minimum value in your original grid, in this example 1
eleRange = is the range of values in your original grid, in this example 1000 - 1 = 999
newRange = is the range in your desired stretch, in this example 10 - 1 = 9
newMin = is the minimum value in your desired stretch value, in this example 1

so what you actually type into a raster calculator is:

(([EleGrid] - 1) / 999) * 9 ) + 1

Re: export raster as stretched value from model builder

XanderBakker — Mon, 15 Feb 2016 17:28:42 GMT

If you would execute this in the Python window, you could use the raster properties min and max of the raster like this:

result = arcpy.sa.Int((arcpy.Raster('DTM_50cm') - arcpy.Raster('DTM_50cm').minimum) / (arcpy.Raster('DTM_50cm').maximum - arcpy.Raster('DTM_50cm').minimum) * 255)

The result may differ from the original stretch result, since stretching normally cuts of a percentage from start and end to optimize the stretch range.