[AstroPy] all-sky map

[Erik Tollerud]

> If anybody knows why the figure size has to be 2:1 to avoid a blank
> image, I'd really appreciate a tip.

Maybe this is a version problem? If I do the following with matplotlib 1.0.1:

import matplotlib
matplotlib.use('agg') #I tried a few other backends and got the same result

from matplotlib.pyplot import figure,axes,imshow,savefig
from numpy.random import randn
from math import pi

img = randn(100,100)

figure(figsize=(10,5))
imshow(img,extent=(-pi,pi,-pi/2,pi/2))
savefig('filename.png')

I get this result: http://dl.dropbox.com/u/8683962/moll-agg1.png

And if I add aspect=.5 to the imshow call, I get
http://dl.dropbox.com/u/8683962/moll-agg12.png

Clearly it is not blank in either case, although the second case is
presumably is what you want.



On Tue, Apr 5, 2011 at 3:56 PM, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi Marsall,
>
> On Tue, Apr 5, 2011 at 2:50 PM, Marshall Perrin <mperrin at stsci.edu> wrote:
>> On Apr 5, 2011, at 12:32 PM, Jonathan Slavin wrote:
>>> I'm looking for a way to plot an all-sky map of modeled data using a
>>> Hammer-Aitoff projection.  The way I've done this in IDL is to create a
>>> uniform x-y grid, translate that l, b using the proper conversion for an
>>> Aitoff projection and generate the data on that grid.  I then display
>>> the image and overlay an Aitoff grid (which I also generate).  So the
>>> image is rectangular and extends beyond the plot edges.  That is fine,
>>> but then all the labeling, etc. has to be done by hand.  Is there an
>>> easier way?  Any help would be appreciated.
>>
>>
>> Check out the matplotlib mpl_toolkits.basemap module.   The Basemap class implements a user-selectable map projection, and yields a callable object which handles the translation between projection coordinate systems and x,y positions for plotting.   Here is some code I recently wrote to do a similar task, plotting positions of objects on an all-sky Mollweide projection:
>
> In theory one should be able to get this going with just the standard
> Matplotlib projections, without basemap, which has a huge dependency
> set.  There seems to be a bug if you don't set the figure to have
> aspect ratio 2:1, but this code works for me, where img is a square
> array.
>
> import matplotlib.figure
> import matplotlib.backends.backend_agg
>
> fig = matplotlib.figure.Figure((10, 5))
> ax = fig.add_subplot(1,1,1,projection='mollweide')
> image = ax.imshow(img, extent=(-pi,pi,-pi/2,pi/2), clip_on=False, aspect=0.5)
> cb = fig.colorbar(image, orientation='horizontal')
>
> cb.set_label(r"$\mathrm{Column}\/\mathrm{Density}\/[\mathrm{g}/\mathrm{cm}^2]$")
> canvas = matplotlib.backends.backend_agg.FigureCanvasAgg(fig)
> canvas.print_figure("allsky.png")
>
> (a bit more discussion:
> http://blog.enzotools.org/yt-development-all-sky-column-density-calcula
> )
>
> If anybody knows why the figure size has to be 2:1 to avoid a blank
> image, I'd really appreciate a tip.
>
> -Matt
>
>>
>>        # define base map class.
>>        map = Basemap(projection='moll', lat_0 = 0, lon_0 = 0,
>>                              resolution = None)  # do *NOT* draw Earth continents at any resolution!
>>        map.drawmapboundary()
>>        p.title("Equatorial coordinates J2000")
>>
>>        # draw and label ra/dec grid lines every 30 degrees.
>>        degtoralabel = lambda deg : "%+d$^h$" % int(deg/15)
>>        degtodeclabel = lambda deg : "%+d$^\circ$" % deg
>>        map.drawparallels(n.arange(-90, 90, 30), fmt=degtodeclabel, labels=[1,0,0,0])
>>        map.drawmeridians(n.arange(0, 360, 30) )  # label these manually since I don't like the default label positions:
>>                                                                                        # this also demonstrates how to overplot text on map coordinates...
>>        for h in [0,6,12,18]:
>>            x,y = map(h*15,0)
>>            p.text(x,y, degtoralabel(h*15))
>>
>>        # draw data points
>>        px, py = map(data.radeg, data.dedeg)
>>        map.plot(px, py, "o", color="red")
>>
>>
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-- 
Erik Tollerud