Added winkel tripel projection class #2442

AgentOxygen · 2024-09-25T02:01:45Z

Rationale

Winkel-Tripel is a popular projection that would be used by multiple users (my group at UT and folks at NCAR). It is also the primary projection for the National Geographic Society.

Implications

I have created a new CRS projection object without modifying any code by utilizing existing class objects and the pyproj backend.

Checklist

The new class object can be utilized in similar fashion to the other projection classes.
I am unsure how to integrate this into the existing test suite, however I imagine it would undergo the same testing as other projections. I am happy to assist with that integration if I could be pointed in the right direction.

This is my first pull request! I am open to input how on to properly contribute.

CLAassistant · 2024-09-25T02:01:51Z

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greglucas

Nice, this looks like a great start.

Regarding the tests: Probably add a test similar to one of the other crs's here containing some transform points and initialization expectations: https://github.com/SciTools/cartopy/tree/main/lib/cartopy/tests/crs

Add the projection to the parameterization list here and add a comparison image.

cartopy/lib/cartopy/tests/mpl/test_mpl_integration.py

Lines 161 to 200 in d57fa13

    
           @pytest.mark.parametrize('proj', [ 
        
               ccrs.Aitoff, 
        
               ccrs.EckertI, 
        
               ccrs.EckertII, 
        
               ccrs.EckertIII, 
        
               ccrs.EckertIV, 
        
               ccrs.EckertV, 
        
               ccrs.EckertVI, 
        
               ccrs.EqualEarth, 
        
               ccrs.Gnomonic, 
        
               ccrs.Hammer, 
        
               pytest.param((ccrs.InterruptedGoodeHomolosine, dict(emphasis='land')), 
        
                            id='InterruptedGoodeHomolosine'), 
        
               ccrs.LambertCylindrical, 
        
               pytest.param((ccrs.Mercator, dict(min_latitude=-85, max_latitude=85)), 
        
                            id='Mercator'), 
        
               ccrs.Miller, 
        
               ccrs.Mollweide, 
        
               ccrs.NorthPolarStereo, 
        
               ccrs.Orthographic, 
        
               pytest.param((ccrs.OSGB, dict(approx=True)), id='OSGB'), 
        
               ccrs.PlateCarree, 
        
               ccrs.Robinson, 
        
               pytest.param((ccrs.RotatedPole, 
        
                             dict(pole_latitude=45, pole_longitude=180)), 
        
                            id='RotatedPole'), 
        
               ccrs.Stereographic, 
        
               ccrs.SouthPolarStereo, 
        
               pytest.param((ccrs.TransverseMercator, dict(approx=True)), 
        
                            id='TransverseMercator'), 
        
               pytest.param( 
        
                   (ccrs.ObliqueMercator, dict(azimuth=0.)), id='ObliqueMercator_default' 
        
               ), 
        
               pytest.param( 
        
                   (ccrs.ObliqueMercator, dict(azimuth=90., central_latitude=-22)), 
        
                   id='ObliqueMercator_rotated', 
        
               ), 
        
           ]) 
        
           @pytest.mark.mpl_image_compare(style='mpl20') 
        
           def test_global_map(proj):

A PR you can look at for updating one of the other projections is #1561

lib/cartopy/crs.py

greglucas · 2024-09-25T02:18:15Z

lib/cartopy/crs.py

+        globe = globe or Globe(semimajor_axis=WGS84_SEMIMAJOR_AXIS)
+        proj4_params = [('proj', 'wintri'),
+                        ('lon_0', central_longitude),
+                        ('lat_0', 0.0)]


Do we need to pass in the lat_0 parameter even if 0 is the default, and does that even work, it looks like it is lat_1 in the documentation: https://proj.org/en/9.4/operations/projections/wintri.html

lat_0 is required and lat_1 doesn't work. Maybe this is a typo in proj? I'm also not very familiar with that library so maybe I'm hacking a parameter.

I don't think lat_0 is required when I tried this out locally. It looks like it may actually be ignored within proj. lat_1 does work for me and is the first standard parallel. For now, I would just remove the lat_0 from this list. In addition, all of our other _WarpedRectangularProjection subclasses also accept the false_easting and false_northing, so could you pipe those through the initializer as well for consistency with the other classes?

Analysis:
All of these produce a pyproj CRS, but there are differences in the WKT which I think the lat_0 indicates isn't being forwarded because it has a "REMARK" at the end. You can also look at the first standard parallel and the first and second are identical, whereas the third (with lat_1) does have the expected 5.

import pyproj pyproj.CRS.from_proj4("proj=+wintri").to_wkt() pyproj.CRS.from_proj4("proj=+wintri +lat_0=5").to_wkt() pyproj.CRS.from_proj4("proj=+wintri +lat_1=5").to_wkt()

'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]' 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]],REMARK["PROJ CRS string: +proj=wintri +lat_0=5"]]' 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",5,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]'

greglucas · 2024-09-25T02:29:40Z

lib/cartopy/crs.py

        return result


+class WinkelTripel(_WarpedRectangularProjection):


Do we need to do any of the nan handling here like we are doing in the Robinson projection? i.e. should this subclass Robinson instead if it is similar to that?

I was able to generate maps containing maps with no problem. Are there other tests for nans that I would need to do?

Co-authored-by: Greg Lucas <[email protected]>

greglucas · 2025-04-13T12:46:50Z

ping @AgentOxygen did you want to try and get this in still? It looks like it needs tests and a possible update to the keyword argument.

AgentOxygen · 2025-04-24T20:45:59Z

Apologies for the delay, I just finished up my master's thesis! I've added the test and an image for comparison. I noticed several of the tests failed, though I'm not sure how to proceed. What are the next steps I should take to get this integrated.

greglucas · 2025-04-28T12:35:03Z

lib/cartopy/crs.py

+        globe = globe or Globe(semimajor_axis=WGS84_SEMIMAJOR_AXIS)
+        proj4_params = [('proj', 'wintri'),
+                        ('lon_0', central_longitude),
+                        ('lat_0', 0.0)]


I don't think lat_0 is required when I tried this out locally. It looks like it may actually be ignored within proj. lat_1 does work for me and is the first standard parallel. For now, I would just remove the lat_0 from this list. In addition, all of our other _WarpedRectangularProjection subclasses also accept the false_easting and false_northing, so could you pipe those through the initializer as well for consistency with the other classes?

Analysis:
All of these produce a pyproj CRS, but there are differences in the WKT which I think the lat_0 indicates isn't being forwarded because it has a "REMARK" at the end. You can also look at the first standard parallel and the first and second are identical, whereas the third (with lat_1) does have the expected 5.

import pyproj pyproj.CRS.from_proj4("proj=+wintri").to_wkt() pyproj.CRS.from_proj4("proj=+wintri +lat_0=5").to_wkt() pyproj.CRS.from_proj4("proj=+wintri +lat_1=5").to_wkt()

'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]' 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]],REMARK["PROJ CRS string: +proj=wintri +lat_0=5"]]' 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["World Geodetic System 1984",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ID["EPSG",6326]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Winkel Tripel"],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Latitude of 1st standard parallel",5,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]'

greglucas · 2025-04-28T14:19:57Z

lib/cartopy/crs.py

+                        ('lat_0', 0.0)]
+
+        super().__init__(proj4_params,
+                                           central_longitude,


Should be indented the same amount as the parentheses, see the other classes in this file for an example.

greglucas · 2025-04-28T14:27:40Z

Apologies for the delay, I just finished up my master's thesis!

🎉 Congratulations, @AgentOxygen!

lib/cartopy/crs.py

Removing unused central latitude

Fixing formatting of super() call

greglucas · 2025-05-23T03:03:07Z

@AgentOxygen, it looks like the image comparison is failing now. I pushed the formatting fix, but otherwise this looks good to go to me once you can update the images to the expected content.

Added winkel tripel projection class

d550f65

AgentOxygen mentioned this pull request Sep 25, 2024

Feature Request: Winkel Tripel projection #1954

Open

greglucas reviewed Sep 25, 2024

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greglucas mentioned this pull request Sep 26, 2024

add a special projection for EPSG:27572 #2427

Merged

Cleaned up WinkelTripel super constructor

6210860

Co-authored-by: Greg Lucas <[email protected]>

AgentOxygen and others added 3 commits April 24, 2025 15:03

Merge branch 'SciTools:main' into main

1511ceb

Added Winkel Tripel test

de76b10

Added baseline image for Winkel Tripel projection

31dc6c7

greglucas reviewed Apr 28, 2025

View reviewed changes

greglucas reviewed May 23, 2025

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greglucas added 2 commits May 22, 2025 20:54

Update lib/cartopy/crs.py

ced358f

Removing unused central latitude

Update lib/cartopy/crs.py

0d1baff

Fixing formatting of super() call

	@pytest.mark.parametrize('proj', [
	ccrs.Aitoff,
	ccrs.EckertI,
	ccrs.EckertII,
	ccrs.EckertIII,
	ccrs.EckertIV,
	ccrs.EckertV,
	ccrs.EckertVI,
	ccrs.EqualEarth,
	ccrs.Gnomonic,
	ccrs.Hammer,
	pytest.param((ccrs.InterruptedGoodeHomolosine, dict(emphasis='land')),
	id='InterruptedGoodeHomolosine'),
	ccrs.LambertCylindrical,
	pytest.param((ccrs.Mercator, dict(min_latitude=-85, max_latitude=85)),
	id='Mercator'),
	ccrs.Miller,
	ccrs.Mollweide,
	ccrs.NorthPolarStereo,
	ccrs.Orthographic,
	pytest.param((ccrs.OSGB, dict(approx=True)), id='OSGB'),
	ccrs.PlateCarree,
	ccrs.Robinson,
	pytest.param((ccrs.RotatedPole,
	dict(pole_latitude=45, pole_longitude=180)),
	id='RotatedPole'),
	ccrs.Stereographic,
	ccrs.SouthPolarStereo,
	pytest.param((ccrs.TransverseMercator, dict(approx=True)),
	id='TransverseMercator'),
	pytest.param(
	(ccrs.ObliqueMercator, dict(azimuth=0.)), id='ObliqueMercator_default'
	),
	pytest.param(
	(ccrs.ObliqueMercator, dict(azimuth=90., central_latitude=-22)),
	id='ObliqueMercator_rotated',
	),
	])
	@pytest.mark.mpl_image_compare(style='mpl20')
	def test_global_map(proj):

		return result


		class WinkelTripel(_WarpedRectangularProjection):

Added winkel tripel projection class #2442

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Added winkel tripel projection class #2442

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AgentOxygen commented Sep 25, 2024

Rationale

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Checklist

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