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How to bypass SSL for PROJ reprojection

A friend was using GDAL’s ogr2ogr command to import some data to PostGIS recently, and as part of the import they were doing a reprojection of the data.

They got the following error:

PROJ: Cannot open https://cdn.proj.org/uk_os_OSTN15_NTv2_OSGBtoETRS.tif: schannel: the certificate or certificate
chain is based on an untrusted root

They’ve had various SSL errors on their computer due to their company’s IT provider providing self-signed root certificates, or screwing up SSL settings in some other way.

She’s waiting for the IT provider to try and sort things out, but as a temporary measure, we managed to find a way to disable SSL verification for PROJ. This obviously reduces security, but I don’t think it’s a major issue as PROJ is just downloading publicly available conversion data to do accurate conversions between different co-ordinate systems. It’s also temporary, until the IT provider sort things out.

Anyway, to bypass SSL verification for PROJ, set the PROJ_UNSAFE_SSL environment variable to 1. For example, with:

export PROJ_UNSAFE_SSL=1

on Linux, or:

set PROJ_UNSAFE_SSL=1

Anyway, there doesn’t seem to be much documentation on this online – I eventually found this Github issue discussion and once I knew the environment variable name, I found it in the PROJ source code. I thought documenting it here may help other people find it.

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This post originally appeared on Robin's Blog.

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Categorised as: Academic, Computing, GIS, How To, Linux, OSX, Remote Sensing, Windows