3D shape, cartography, and geoid of Comet 67P C-G |
3D shape, cartography, and geoid of Comet 67P C-G |
Aug 6 2014, 02:11 PM
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#1
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Solar System Cartographer Group: Members Posts: 10192 Joined: 5-April 05 From: Canada Member No.: 227 |
Explorer 1 said:
"A 2D map of C-G seems like a tough order; the projection math alone..." Don't worry! If you can put a grid on the surface (as we have seen already), you can warp that grid into any map projection you like. Mapping will be no huge problem - in fact I expect they have a rough one already (I've been playing with one myself). Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Aug 10 2014, 06:03 PM
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#2
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
For 67P/C-G, and similarly asymmetric bodies, I'd suggest a projection on an appropriate gravitationally equipotential surface, either respecting the centrifugal forces, or using the body at rest.
"Appropriate" means, the average height of the topography over the equipotential surface should be zero, if possible. As a constraint a surface should be taken, which consists of one component without singularities (and without overlapping itself, which is probably a corollary). Projections go along the field lines of gravity. The result is still a non-planar map. This could be projected in a second step to planar tiles/stripes (mercator-like in a very general sense) by constraining the intrinsic curvature. The width of the stripes would vary because of the varying intrinsic curvature. ... just to close this gap preliminarily, until an official decision is made. |
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Aug 10 2014, 06:38 PM
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#3
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Senior Member Group: Members Posts: 4252 Joined: 17-January 05 Member No.: 152 |
Projections go along the field lines of gravity. Why along the field lines (and with respect to an equipotential surface)? That would rely to some extent on knowledge of the internal mass distribution, which may be significantly nonuniform, and at the very least would require nontrivial numerical modelling to determine. It would strike me as a good property of a projection to depend only on the geometry of the body's surface. But all of this is probably moot since such bodies have been mapped in the past. In practice, I'd guess the projection would be tailored to the body, since some projections may not work for bodies when the surface "folds back on itself". |
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