[GIS] Compressing map algebra outputs from ArcPy

arcgis-10.0arcpymap-algebraspatial-analyst

When creating a raster map algebra output, is it possible to set its compression?

I'm creating a model which generates many hundreds of rasters, and currently each is being stored without any compression which quickly adds up. I expected to be able to use arcpy.env.compression but that seems to have no effect. Example script which produces this behavior:

import arcpy

arcpy.env.compression = 'LZW' # supported by GeoTIFF and most packages

map = Raster("raster.tif") + 100
map.save("raster_plus_100.tif") # would expect this output to have compresssion

Best Answer

I think the problem is that arcpy.env settings only apply to tools. Calling a method on an object is not technically a "tool". In a practical sense, the arcpy.env settings should apply to stuff like Raster.save() but it doesn't appear to work that way.

I was able to save a raster with compression by using arcpy.CopyRaster_management(). Something like this:

arcpy.env.compression = 'LZW'
t1 = arcpy.Raster('sample.tif') + 100
arcpy.CopyRaster_management(t1, 't1.tif')
del t1

Related Solutions

[GIS] Adding two rasters using map algebra in ArcPy

What @Joseph says. The Raster class needs a string containing the path to your raster. You've correctly assigned this to a variable, so you then need to pass those variables to instantiate your Rasters. This code should work:

import arcpy
from arcpy import env
from arcpy.sa import *
raster1 = ("C:/raster1")
raster2 = ("C:/raster2")

#Note lack of quotes in following line
raster3 = Raster(raster1) + Raster(raster2)

#Don't forget to save eg:
raster3.save("C:/raster3")

The reason the documentation you link shows the rasters being passed to map algebra statements in quotes is because they assume you are typing in the python console in ArcMap. If you're raster datasets are open in ArcMap you can refer to them by their name in the table of contents, using quotes.

In which case the necessary code would be

import arcpy
from arcpy import env
from arcpy.sa import *

#No need to assign paths to variables.
#NB You still need to call `Raster()` in order to tell Arcpy that the '+' is for raster math. 
raster3 = Raster("raster1") + Raster("raster2")

#Don't forget to save eg:
raster3.save("C:/raster3")

Best Answer

Related Solutions

[GIS] Adding two rasters using map algebra in ArcPy

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