How can I read MrSID files in Python (using gdal)?

Question

I have to read a large number of MrSID images and process them in Python. I usually access GIS file formats using the gdal application and the gdal Python library. However, the gdal package for Python does not come with MrSID support (I use the portable WinPython and the precompiled gdal package from here). Then I also use QGIS that comes with gdal support: here, gdal does support MrSID out of the box (command: gdalinfo.exe --formats).

I was wondering if there is a gdal package for Python that does support MrSID out of the box, or do I have to compile it from the source (using Windows 8.1 64-bit).

I tried to just copy the QGIS dll "...\gdalplugins\gdal_MrSID.dll" to the same folder in my Python gdal library, but this makes the command "gdalinfo.exe --formats" to stop with an error.

This is the code that I use in Python to see if gdal supports MrSID:

import gdal
gdal.AllRegister()
for i in range(1, gdal.GetDriverCount()):
 drv = gdal.GetDriver(i)
 print drv.GetDescription(),

Using this after implementing Kersten's solution, the list does not include the entry "MrSID". Calling the command "gdalinfo --formats" however, does list the entry "MrSID (rov): Multi-resolution Seamless Image Database (MrSID)".

• Kersten: You should be able to copy the complete osgeo/gdal from your QGIS Python installation to your WinPython installation.
• user52724: Thanks but I wish it was that simple. Are you familiar with a typical QGIS installation on Windows (company policy: I have to use the standalone installer, not the OSGeo4W network installer). I looked and osgeo/gdal related files seem to be spread out everywhere. But is this plain copy and paste approach the right thing to do anyway? How about versions and stuff (both Pythons are 2.7 though)?
• Kersten: In that case it is more complicated. I have a Osgeo4W QGIS installation and successfully ported gdal from the osgeo-python to my stand alone python. I'm sure that is not the best approach but it works.
• user52724: Ok, thanks for sharing. I'll try it at home, where I have Osgeo4W as well. If it works there, your contribution will be marked the solution.
• Kersten: I think the better solution is to use the GDAL binaries from GISinternals (see my answer), unless you want to compile it from source.

Answer 1

Can't you call it with subprocess?

https://docs.python.org/2/library/subprocess.html

• user52724: I have never used subprocess but just reading about it: don't you think this is a bit far-fetched? You want me to call the gdal-related commands from QGIS (with MrSID support) from within Python, right?
• Matthieu: I think I've misread your question in the first place and what you mention was not what I meant. How you say it is definitely far-fetched but it could actually work.
• user52724: Yeah, rereading my question, I understand your answer now. However, it is not what I am looking for, even though it should work. Just for clarity: I want to read + process the MrSID images from within Python using the Python gdal package in the most pythonic way possible.

Answer 2

Instead of using the binaries provided by Christopher Gohlke you can use the GDAL binaries from GISInternals:

For your case you would need:

• GDAL core
• MrSID plugin
• GDAL Python 2.7 bindings

• user52724: Unfortunately, I have to unmark this the solution (for now). I installed these binaries, and gdal is available for my version of Python, however, MrSID is not a raster format available in Python. MrSID is listed in the output of "gdalinfo --formats", but not when executing the code that I have added to my original question. And I am using the same gdal installation in both cases. Any idea why gdal itself supports MrSID but gdal via the Python binding is not?
• user52724: My issue with the binaries from GISInternals was never resolved, but I found a workaround to solve my problem. I create my images using MapServer and access them from Python using WMS. My installation of MapServer does support reading MrSID images. I leave this issue open to be resolved in the future.
• Kersten: Have you tried opening MrSID files from within Python? When I compare my driver lists there are also some inconsistencies - e.g. VRT is missing from the Python list. It is however no problem to open VRT from within the Python bindings.
• user52724: Yes, I tried opening the MrSID files from within Python. I got the error that a 'sid' file is an unsupported format. I made my own comparison list. Here it is: formats supported by GDAL and not by Python binding: FITS, MrSID and VRT. And formats supported by Python binding but not by GDAL directly: OGDI.