[gdal-dev] How to read all metadata from GeoTIFF file?

[krikr42]

Hi,

I have two tiff images, of which the first one is a GeoTIFF image and the
second is a tiff image created from the first one by opening it with pyvips
in Python, modifying it (blurring it) and saving it as a new file (so I
don't know whether the second image counts as a GeoTIFF file). However, the
second image lacks a lot of metadata that exists in the first image which I
need, such as the coordinate system and corner coordinates.

How can I read this metadata from the first file with GDAL (in Python,
although I guess the C++ API is pretty similar)? I have already tried
loading the file as a GDAL dataset using  gdal.Open
<https://gdal.org/python/osgeo.gdal-module.html>   and reading the data with
the  GetMetadata
<https://www.gdal.org/classGDALMajorObject.html#a8ce3bf5795bbebfe9bc643e2152bb360>  
method, and I have looked in the  domains
<https://www.gdal.org/gdal_datamodel.html>   'SUBDATASETS',
'IMAGE_STRUCTURE', 'RPC', 'IMAGERY' as well as the default domain, but none
of those contain the information about the coordinate system or the
coordinates. There are supposedly also xml: domains, and I'm wondering
whether the data I'm looking for may be under an xml domain, but I don't
know what the name of that domain would be, and I can't find any way to list
available domains (is there any? Because that would be great).

So, how can I read the metadata specifying the coordinate system and corner
coordinates from the first file and write it to the other? If I can read it
with GetMetadata, I suppose I will also be able to write it with 
SetMetadata
<https://www.gdal.org/classGDALMajorObject.html#a61ab7226d95b20e3e1f42461a1f62906>  
(I was able to do that for the domains listed above).

I have also tried to transfer the information by reading it with the command
line tool gdalinfo and writing it with gdal_translate, but that fails as 1)
I don't know how to write all the relevant metadata with gdal_translate and
2) the metadata that I try to write isn't successfully written as the
coordinate system information – which looks to be JSON-formatted – ends up
with a different JSON-tag in the root element and with some elements
missing.

Regards

Kristofer



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