[PROJ] Dealing with different versions of PROJ along time

[Javier Jimenez Shaw]

Sorry for the not very clear subject. I don't find a short way to summarize
my problem.

The long description could be "Dealing with different versions of PROJ when
creating web mercator tiles and in a later version PROJ (or EPSG) is using
a different transformation"

Let's say I have a GeoTIFF in "HD72 / EOV" on my server. I generate
web-mercator tiles with gdal2tiles one day (to show it in a browser
online), where I am using PROJ 7.0.1.
I also have some other info (markers, GCPs) stored in "HD72 / EOV". To
display those markers in the browser, I convert them on the fly. (btw, all
in python).

Later I update the version on my server to PROJ 7.2.0. When I transform the
marker coordinates to web-mercator to display them in the browser, the
marker does not fit exactly where it was before with the image. Just an
update in the server PROJ version made the location in the browser
different (between the image and the marker).

See that I am not running gdal2tiles again. The tiles stay with the
transformation selected by PROJ 7.0.1
Also I display every coordinate (the numbers I mean) in "HD72 / EOV".
Web-mercator is used mainly to interact with the browser with a javascript
library (openlayers).

Running
projinfo -s "HD72 / EOV" -t "WGS84 / Pseudo-Mercator"
with both versions, I see that in proj 7.0.1 it is using the transformation
"HD72 to WGS 84 (3)" while in 7.2.0 it is using "HD72 to WGS 84 (4)".
Similar but not the same.

I understand that PROJ criteria to choose automatically a transformation
may change. EPSG can change too, or new transformations may appear. I am
not complaining about that.

How can I solve this discrepancy? Regenerating all the tiles every time I
update PROJ could be expensive for every GeoTIFF. That would end up not
updating PROJ as often as wanted.
My problem is not the accuracy, but the consistency along the time.

Anybody had a similar problem? Any suggestion is welcome.

Thanks.
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.
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