ENH: Azimuthal rotation for Orthographic projection #2504
Conversation
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I'm guessing you'll need to put a version gate around this parameter so that we only use it if the underlying PROJ library >= 9.5. Here is an example in our tests cartopy/lib/cartopy/tests/test_crs.py Line 95 in 0c51cbb What happens if we pass this parameter to the projection in earlier versions, do we get a warning or do we need to issue a warning on our side that the parameter has no effect and will be ignored? |
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ping @kenhira , are you able to add the version gate on this parameter? |
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Apologies for my slow response. I have implemented the version gate (
I tested on my end with |
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Here is what the output is like: However, with the older proj (tested with Here is the test code used for plots above: import matplotlib.pyplot as plt
import cartopy.crs as ccrs
from cartopy.geodesic import Geodesic
if __name__ == "__main__":
anchorage_lon, anchorage_lat = -149.9003, 61.2181
denver_lon, denver_lat = -104.9903, 39.7392
geod = Geodesic()
heading = geod.inverse((anchorage_lon, anchorage_lat), (denver_lon, denver_lat))[0][1]
fig = plt.figure(figsize=(8, 4))
ax1 = fig.add_subplot(1, 2, 1,
projection=ccrs.Orthographic(central_longitude=anchorage_lon,
central_latitude=anchorage_lat))
ax1.coastlines()
ax1.set_global()
ax1.plot([anchorage_lon, denver_lon], [anchorage_lat, denver_lat],
transform=ccrs.Geodetic(), label="Anchorage to Denver")
ax1.plot(anchorage_lon, anchorage_lat, 'o', transform=ccrs.Geodetic(), label="Anchorage")
ax1.plot(denver_lon, denver_lat, 'o', transform=ccrs.Geodetic(), label="Denver")
ax1.set_title("azimuth=0")
ax2 = fig.add_subplot(1, 2, 2,
projection=ccrs.Orthographic(central_longitude=anchorage_lon,
central_latitude=anchorage_lat,
azimuth=heading))
ax2.coastlines()
ax2.set_global()
ax2.plot([anchorage_lon, denver_lon], [anchorage_lat, denver_lat],
transform=ccrs.Geodetic())
ax2.plot(anchorage_lon, anchorage_lat, 'o', transform=ccrs.Geodetic(), label="Anchorage")
ax2.plot(denver_lon, denver_lat, 'o', transform=ccrs.Geodetic(), label="Denver")
ax2.set_title("azimuth=%.2f deg" % heading)
ax2.legend(loc='lower right')
fig.tight_layout()
plt.savefig('test_plot.png')
plt.show() |
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Thanks @kenhira! That all looks good to me. |
Rationale
This update adds
azimuthargument toccrs.Orthographic(), with a corresponding test. It will enable users to rotate the projection around the central point. It uses new Proj parameteralpha, which was added toOrthographicin Proj version 9.5.0.https://proj.org/en/stable/operations/projections/ortho.html
An equivalent
azimuthargument has already been implemented toccrs.ObliqueMercator().Implications
Users will become able to rotate the map as they prefer. For example, one can orient a satellite image along the solar direction to emphasize which direction the sun glint and shadow appear.
This update is a minimal update, adding just one argument to the function.