Wrong extent on teardrop plot

[SmirnGreg]

Hi @richteague,

There is an issue (or my misunderstanding) with a teardrop plot extent. The extent keyword in the matplotlib's imshow sets the location of the image borders, not the location of the image corner pixels' centers.

https://github.com/richteague/gofish/blob/8b1a6637c42692e2363fd63c2c17580b15afb7bf/gofish/gofish.py#L2159

In your case, rvals are the locations of the bin centers, right? For example, the can be:

 2.01438614 2.3242917  2.63419726 2.94410282 3.25400838 3.56391393
 3.87381949 4.18372505 4.49363061 4.80353617 5.11344173 5.42334729
 5.73325285 6.04315841 6.35306397 6.66296953 6.97287509 7.28278065 

That namely means that the pixel centers are (I will round) 0.15, 0.45, 0.75, ..., with a pixel size 0.3. In this case, the desired extent in the radial coordinate will be from the first rval - 0.15 to the last rval + 0.15.

If you want to keep imshow, the extent should be changed to:

velstep = velax[1] - velax[0]
rstep = rvals[1] - rvals[0]
extent = [velax[0] - velstep / 2, velax[-1] + velstep / 2, 
          rvals[0] - rstep / 2, rvals[-1] + rstep / 2]

The corresponding tutorial: https://matplotlib.org/3.1.1/tutorials/intermediate/imshow_extent.html

I would propose though to use the method pcolormesh, as it also can handle not-uniform coordinate steps. (shading='gourand') can be used if the coordinates are left as is, or the coordinates can be rewritten to correctly match the edges of the pixels.

https://matplotlib.org/3.1.1/api/_as_gen/matplotlib.pyplot.pcolormesh.html

Best,
Greg

[richteague]

Ah yes, you're absolutely correct. I'll make that change. I have noticed that there's also an issue if you use resample where the spectra returned are on slightly different axes, particularly small radii. I'll look into fixing that and explore the use of pcolormesh. I'm not familiar with it but will check it out!