[AstroPy] all-sky map

Erik Tollerud erik.tollerud at gmail.com
Thu Apr 7 02:15:28 EDT 2011


Whoops, sorry, you're aboslutely right - I left out a very important
line!  The corrected version (the key change being the addition of the
call to "axes" with the projection keyword) is:

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))
axes(projection='mollweide')
imshow(img,extent=(-pi,pi,-pi/2,pi/2))
savefig('filename.png')



Also, when I run your script you linked to, I get the following three
images (tested both on a Snow Leopard Mac and Ubuntu Lucid, both with
matplotlib 1.0.1):
http://dl.dropbox.com/u/8683962/allsky1.png
http://dl.dropbox.com/u/8683962/allsky2.png
http://dl.dropbox.com/u/8683962/allsky3.png

And as you can see, 2 and 3 have colored imshow ovals rather than
blank.  This makes me think this is a bug that was fixed at some point
(if you're using a version earlier than 1.0.1), or some rendering
problem that is platform-specific (if you're using something other
than OS X or Linux)... Definitely very weird behavior, though!


On Wed, Apr 6, 2011 at 4:08 PM, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi Eric,
>
> On Wed, Apr 6, 2011 at 8:49 AM, Erik Tollerud <erik.tollerud at gmail.com> wrote:
>>> 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.
>
> Yup, that works for me, but it doesn't apply the Mollweide projection.
>  I put up a paste here:
>
> http://dpaste.com/hold/529372/
>
> I run this, and allsky1.png has the image.  allsky2.png and
> allsky3.png both have empty ovals, and it's not clear to me what's
> causing that.
>
> -Matt
>
>>
>>
>>
>> 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
>>
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-- 
Erik Tollerud



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