Hi Mario,
(Sorry for the reply to a reply, but I was not on the list when the original
message was posted)
This may not be useful for Basemap, but I did this with the
matplotlib.projections.geo HammerAxes projection. I got it to work by
subclassing that and modifying the _get_affine_transform() to negate the x-axis
scale. I also seem to have had to fiddle with _set_lim_and_transforms() to
account for this, though I don't remember the details.
In any case, I don't know how Basemap works and whether this is helpful. Maybe
as inspiration... The code is below if it helps.
joey
On Sep 18, 2010, at 6:02 AM, Jeff Whitaker wrote:
> On 9/16/10 12:38 PM, Mario Juric wrote:
>> Hi,
>> I'm looking at Basemap as a backend for plotting maps of the sky in
>> different projections, and so far it seems like a really good match!
>> Excellent work!
>>
>> The only problem that I don't know how to solve is that in astronomy
>> the longitude on maps typically increases from right to left (we're
>> looking at the celestial sphere from the "inside"). Is there any way (or
>> a trick) to make Basemap do this?
>>
>> Regards,
class AstroHammerAxes(HammerAxes):
"""Astronomical hammer projection.
This is just a Hammer projection with the longitude axis
reversed left-right.
"""
name='astrohammer'
def _get_affine_transform(self):
"""get affine transform
This is cribbed from GeoAxes, but negates the xscale
to put positive longitude to the left. Not sure this
is actually robust.
"""
transform=self._get_core_transform(1)
xscale,_=transform.transform_point((pi,0))
_,yscale=transform.transform_point((0,pi/2.0))
return Affine2D()\
.scale(-0.5/xscale, 0.5/yscale)\
.translate(0.5,0.5)
def _set_lim_and_transforms(self):
HammerAxes._set_lim_and_transforms(self)
yaxis_stretch = Affine2D().scale(pi * 2.0, 1.0).translate(pi, 0.0)
yaxis_space = Affine2D().scale(1.0, 1.1)
yaxis_text_base = \
yaxis_stretch + \
self.transProjection + \
(yaxis_space + \
self.transAffine + \
self.transAxes)
self._yaxis_text1_transform = \
yaxis_text_base + \
Affine2D().translate(-8.0, 0.0)
self._yaxis_text2_transform = \
yaxis_text_base + \
Affine2D().translate(8.0, 0.0)
# register the projection on import
register_projection(AstroHammerAxes)
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