[GIS] Performing Raster Calculator functions using Python and open source modules

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I would like to perform mathematical functions similar to those you would use Raster Calculator for in ArcMap, however I'd like to do it in Python without using the ArcpPy module. I have the osgeo module, and it seems like it should be possible to do however I'm having a hard time finding any useful syntax.

An example function would be to multiply every cell value in an input raster by 2.

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Without reinventing the wheel, I suggest you to use gdal_calc.py. Example:

gdal_calc.py -A input.tif --outfile=result.tif --calc="A*2"

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[GIS] Performing raster map algebra in open source web GIS

Using only open source software, you will almost certainly need to do some programming yourself. GDAL is the de facto open source raster I/O library, so you will probably be using it or one of its many wrappers. You could use Python (e.g. rasterio + numpy/scipy) or node.js, e.g. node-gdal (though beware it is currently synchronous/blocking). As for actually implementing it as a web service, I'm not sure what would be the best approach, but there is a related question here: Comparing different open source GIS servers?

If programming isn't your thing, you might take a look at FME Server. It's a commercial product but probably substantially cheaper than ArcGIS Server, and it has all sorts of raster calculation transformers, so I would be quite surprised if they could not accomplish what you need to do. You would not need to load the rasters into a database as it can read from just about any raster file format.

The server part would allow you to run the transformations (FME workspaces) on a server and use an API, e.g. the FME Server REST API, to initiate those transformations and access the results.

The main benefit is you would not need to do much if any programming to get the services up and running, just a little front-end coding to work with the API.

GDAL Calc – gdal_calc Raster Calculator Syntax for Logical Operators and Other Functions

In the source for gdal_calc.py, the calculation is made directly using eval:

myResult = eval(opts.calc, global_namespace, local_namespace)

That would suggest that any well-formed expression that also evaluates on the command line will work. According to the documentation, you may use gdalnumeric syntax with +-/*, and/or numpy functions. You can test your functions using small dummy arrays in the interactive shell, then use the same calls in gdal_calc.

Keep in mind that chaining together multiple numpy functions is likely to produce temporary in-memory arrays that can substantially increase memory usage, especially when dealing with large images.

You can look at the numpy documentation for a list of all the functions: routines. The ones you are after are likely here: math or here: routines.logic.

This is where functions like minimum are coming from, it's just that the namespace is already imported. Really, it's numpy.minimum, etc

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[GIS] Performing raster map algebra in open source web GIS

GDAL Calc – gdal_calc Raster Calculator Syntax for Logical Operators and Other Functions

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