add EPSG:31370

[tcarion]

reference: https://epsg.org/crs_31370/BD72-Belgian-Lambert-72.html

[tcarion]

the conversion method use Lambert Conic Conformal, but I couldn't find reference to it in the code. Is it currently missing?

[juliohm]

Thank you for the PR @tcarion !

the conversion method use Lambert Conic Conformal, but I couldn't find reference to it in the code. Is it currently missing?

That is right. We need to implement the formula first, in order to attach the correct CRS type to the EPSG code instead of the generic Cartesian2D.

The formula is well-documented in the link shared, but I would make sure they match the formulas in the official EPSG guide. Do you think you have some time to work on this new LambertConic type?

[tcarion]

Sure, I can try to help!

Do you think I should do this here or rather create another PR?

[juliohm]

Another PR would be great. That way we can focus the review on the formulas and behavior. You could leave this PR open and rebase later after the formula is available.

Em qua., 30 de abr. de 2025, 09:56, Tristan Carion @.***> escreveu:

tcarion left a comment (JuliaEarth/CoordRefSystems.jl#263) https://github.com/JuliaEarth/CoordRefSystems.jl/pull/263#issuecomment-2841886971

Sure, I can try to help!

Do you think I should do this here or rather create another PR?

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[juliohm]

@tcarion I believe we can map the new CRS type to the EPSG code now 🙂

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.85%. Comparing base (395b9c1) to head (c81d172). Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/datums.jl	0.00%	1 Missing :warning:

Additional details and impacted files

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##             main     #263      +/-   ##
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  Lines        1754     1755       +1     
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[tcarion]

For the parameters, I changed them to be the same as the projstring given by proj:

$ projinfo EPSG:31370
PROJ.4 string:
+proj=lcc +lat_0=90 +lon_0=4.36748666666667 +lat_1=51.1666672333333 +lat_2=49.8333339 +x_0=150000.013 +y_0=5400088.438 +ellps=intl +units=m +no_defs +type=crs

Do you think I should precise this in the comments?

Also, I would like to add the transformation from BD72 to WGS84 in transforms.jl. I used the parameters from this page, but it gives slightly different results than Proj, which makes the test fail

[juliohm]

Do you think I should precise this in the comments?

Perhaps a short comment explaining the choice can help future contributors. We can explain that the EPSG database shows parameters in DMS, and because of that we opted for the C PROJ parameters.

Also, I would like to add the transformation from BD72 to WGS84 in transforms.jl. I used the parameters from this page, but it gives slightly different results than Proj, which makes the test fail

That could be done in a separate PR for better review.