Refactor WCS handling

[astrofrog]

This is work in progress, and includes the refactoring carried out during the ALMA software development workshop at NRAO.

cc @ChrisBeaumont - there are still a couple of things to add, but this will then be ready for you to test with glue and optimize if needed.

[astrofrog]

@ChrisBeaumont - this is ready for testing in Glue if you are interested. You now no longer need the WCSSlice object. You can do:

fig = plt.figure()
ax = WCSAxes(fig, [0.1, 0.1, 0.8, 0.8], w, slices=(100, 'y', 'x'))
fig.add_axes(ax)
ax.imshow(image[:,:,100].transpose(), cmap=plt.cm.gist_heat)

if you want to show a grid, you can, but when you call grid() you should pass the grid_type='contours' option. The grid will likely slow things down, so you are better off not using it if not needed.

Regardless of the grid type, all other transformations are now pixel to world, so should work on any arbitrary slices and images with distortions!

[ChrisBeaumont]

cool, will try to look at this tomorrow

[ChrisBeaumont]

Playing with this now, a few things seem broken:

• RA ticks are bonkers
• Extra unlabeled Dec ticks
• X axis formatting on bottom + top, not just bottom

I'll keep investigating

from astropy.io import fits
from astropy.wcs import WCS
from wcsaxes import WCSAxes
import matplotlib.pyplot as plt

data = fits.open('/Users/beaumont/perseus/12co.fits')[0].data
wcs = WCS('/Users/beaumont/perseus/12co.fits')

fig = plt.figure()
ax = WCSAxes(fig, (.1, .1, .8, .8), wcs, slices=(100, 'y', 'x'))
fig.add_axes(ax)
ax.imshow(data[100, :, :], vmin=0, vmax=5)
plt.savefig('test.png')

[astrofrog]

@ChrisBeaumont - can you share the file?

[ChrisBeaumont]

https://www.dropbox.com/s/wpr4wfavrif0q9u/12co.fits

On Mon, Apr 21, 2014 at 4:01 PM, Thomas Robitaille <notifications@github.com

wrote:

@ChrisBeaumont https://github.com/ChrisBeaumont - can you share the
file?

—
Reply to this email directly or view it on GitHubhttps://github.com//pull/24#issuecomment-40970788
.

---

Chris Beaumont
Graduate Student
Institute for Astronomy
University of Hawaii at Manoa
2680 Woodlawn Drive
Honolulu, HI 96822
www.ifa.hawaii.edu/~beaumont

---

[astrofrog]

@ChrisBeaumont - the solution turned out to be very simple - the slices argument is in the wrong order, so you are getting velocity ticks (which explains the values). Try using slices=('x', 'y', 100) and it should work better. I'm not sure what the best way to avoid this. Documentation? Or do you think the order is unnatural?

[astrofrog]

@ChrisBeaumont - I nevertheless found a few small things that should be fixed - namely that in this case, only the ticks for the non-sliced coordinate should be shown by default. I've pushed a fix.

[ChrisBeaumont]

Need a graceful fallback here for slices=None. Something like for coord_index in range(len(slices or []))

[astrofrog]

Fixed

[ChrisBeaumont]

Extent isn't iterable, but list-like (you need random access)

[ChrisBeaumont]

I proposed some improvements and a bugfix in #25, but otherwise this looks good to me!