regression bug in cartopy 0.20?, as_geocentric() not functionning as expected

[dja001]

Description

I use cartopy.crs.Geodetic().as_geocentric() to get x,y,z coordinates from lat/lon. Since the introduction of cartopy 0.20, this functionality appears to be broken with the returned z-component always zero.

Code to reproduce

The problem can be reproduced with a few lines of code:

import numpy as np
import cartopy

crs = cartopy.crs.Geodetic()
geo_cent = crs.as_geocentric()

out = geo_cent.transform_points(crs, np.array([0.]), np.array([45.]))
print('[x,y,z] from lon=0, lat=45 : ', out)

In cartopy 0.19, output is :

[x,y,z] from  lon=0, lat=45 :  [[4517590.87884893       0.         4487348.40886592]]

as expected.

In cartopy 0.20 output is:

[x,y,z] from lon=0, lat=45 :  [[4517590.87884893       0.               0.        ]]

with the z component equal to zero while it should not.

Operating system

linux

Cartopy version

Problem in 0.20

conda list

Test environments created with:
conda create -n cartopy19 -c conda-forge cartopy=0.19.0.post1
and
conda create -n cartopy20 -c conda-forge cartopy

[guziy]

It seems like in 0.20 z computed only if z is provided as input...

In [18]: import numpy as np
    ...: import cartopy
    ...:
    ...: crs = cartopy.crs.Geodetic()
    ...: geo_cent = crs.as_geocentric()
    ...:
    ...: out = geo_cent.transform_points(crs, np.array([0.]), np.array([45.]), np.array([0]))
    ...: print('[x,y,z] from lon=0, lat=45 : ', out)
[x,y,z] from lon=0, lat=45 :  [[4517590.87884893       0.         4487348.40886592]]

[guziy]

I agree with Dominik, It should be computed every time it is returned...

[greglucas]

Likely because of this check:

cartopy/lib/cartopy/crs.py

Lines 51 to 53 in 970b3f0

	if z is None:
	xx, yy = transformed_coords
	zz = 0

A PR to update this would be welcome!

[dja001]

Thanks a lot everyone for contributing to fixing this!