From: Eric Hivon <hivon@ia...> - 2013-08-09 09:38:33
if you have a question on Healpix, please write to Healpix-support@... or visit http://healpix.sourceforge.net
Concerning your question, Healpix can be used for any data on the sphere, whether the sphere is seen from the inside
(like the sky) or from the outside (like a planet, or an atom).
The only trick is that the visualization routine should know what is the point of view of the observer,
because in one case the longitude increases rightward (when looking the sphere inwards) while in the other it increases leftward
(when looking outwards, as astronomers do). In the simplest case, it is just a left-right flip of the image.
Most Healpix visualization routines can adopt either point of view thanks to a flag (with the default being an outward observation),
as in Andrea's example.
You can find another example of it generated with Healpix-IDL routine orthview at the bottom of
and at http://healpix.sourceforge.net/images/earth_0250px_movie.gif
The original TUG87 5x5arcmin model used to generate that image do not seem to be online anymore (but we have Healpix FITS maps of it)
and it is superseded by Etopo1 1x1arcmin data at
On Aug 8, 2013, at 9:11 PM, Andrea Zonca wrote:
> hi Ian,
> have you checked basemap?
> It has been specifically developed for plotting data on top of Earth background.
> However, you could do something similar in healpy...I couldn't resist
> to try it out, see:
> On Wed, Aug 7, 2013 at 8:26 PM, Ian Douglas <iandouglas736@...> wrote:
>> Forgive my question, I know this might not be the correct avenue, but I'm
>> looking at various coordinate systems that could project a map of equal-area
>> blocks (and are the centers equidistant as well?), but for looking down at a
>> planet, instead of upward like a "sky" view.
>> For example, I'd love to project something over Earth where I could figure
>> out which pixel resolution would equate to roughly 5 square miles or 20
>> square miles, and then translate a set of latitude/longitude coordinates to
>> a pixel reference. Or, given two pixel references, calculate their lat/lng
>> centers and do a simple "as the crow flies" distance calculation between the
>> two centers.
>> If HEALPix, and healpy, do something similar to that already, then great.
>> I'm just not sure where to find FITS data for the planet itself, all I can
>> seem to find are star maps, temperatures, etc., of space as if you're on the
>> planet looking outward.
>> Thanks for any ideas,
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