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Add the Spilhaus projection to the supported GMT projections#4657

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Add the Spilhaus projection to the supported GMT projections#4657
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@Chuan1937 Chuan1937 commented May 25, 2026

@Chuan1937 Chuan1937 self-assigned this May 25, 2026
@Chuan1937 Chuan1937 added this to the 0.19.0 milestone May 25, 2026
Comment thread doc/techref/projections.md Outdated
Comment thread examples/projections/misc/misc_spilhaus.py
Chuan1937 and others added 2 commits May 26, 2026 13:01
Co-authored-by: Dongdong Tian <seisman.info@gmail.com>
Comment thread examples/projections/misc/misc_spilhaus.py Outdated
Chuan1937 and others added 2 commits May 27, 2026 12:17
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seisman commented May 28, 2026

It seems filling water/land masses are not 100% correct for the Spilhaus projection.

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It seems filling water/land masses are not 100% correct for the Spilhaus projection.

Looks like this is an know issue, see GenericMappingTools/gmt#8745 (comment).

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seisman commented Jun 3, 2026

It seems filling water/land masses are not 100% correct for the Spilhaus projection.

Looks like this is an know issue, see GenericMappingTools/gmt#8745 (comment).

Maybe we can just plot the coastlines in this example, and add a note that filling land/water doesn't work well?

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It seems filling water/land masses are not 100% correct for the Spilhaus projection.

Looks like this is an know issue, see GenericMappingTools/gmt#8745 (comment).

Maybe we can just plot the coastlines in this example, and add a note that filling land/water doesn't work well?

So far so good

@seisman seisman added documentation Improvements or additions to documentation needs review This PR has higher priority and needs review. labels Jun 4, 2026
Comment thread examples/projections/misc/misc_spilhaus.py Outdated
Chuan1937 and others added 2 commits June 5, 2026 11:33
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seisman commented Jun 6, 2026

Please add a note that this projection works well for coastlines but has issues for filling land/water masses.

@seisman seisman added final review call This PR requires final review and approval from a second reviewer and removed needs review This PR has higher priority and needs review. labels Jun 6, 2026
Comment thread doc/techref/projections.md Outdated
oceans as one contiguous body of water, with Antarctica at the top. It was
developed by Athelstan Spilhaus and is useful for oceanographic studies.

**+proj=spilhaus+width=**\ *width*
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Propably more a GMT related question: But still wondering why the synthax for this projection is different comparted to the other projections (see also the text at https://pygmt-dev--4657.org.readthedocs.build/en/4657/projections/index.html#projections). Why we do not use something like Sp/width ?

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Because GMT is running out of single-letter codes for map projections. -JS is for already used by General stereographic projection. Using -JSp may be more confusing.

Co-authored-by: Yvonne Fröhlich <94163266+yvonnefroehlich@users.noreply.github.com>
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Add the Spilhaus projection to the supported GMT projections

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