Timeline for What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation?
Current License: CC BY-SA 2.5
16 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jan 6, 2012 at 16:41 | history | edited | whuber |
edited tags
|
|
| Jul 20, 2011 at 20:53 | answer | added | cffk | timeline score: 2 | |
| Jul 11, 2011 at 20:43 | answer | added | cffk | timeline score: 4 | |
| Mar 17, 2011 at 3:59 | history | edited | Dan S. | CC BY-SA 2.5 |
Added citation relevant to the discussion on some of the answers.; added 4 characters in body
|
| Feb 11, 2011 at 21:03 | vote | accept | Dan S. | ||
| Feb 10, 2011 at 18:17 | answer | added | whuber | timeline score: 6 | |
| Feb 4, 2011 at 21:00 | history | edited | Dan S. | CC BY-SA 2.5 |
added 95 characters in body
|
| Feb 4, 2011 at 20:58 | comment | added | Dan S. | @Kirk: I'm not saying to use straight 3D lines, just a 3D orthographic coordinate system. ;) For example, a great circle on the sphere is the intersection of a plane with the surface of the sphere. Want to find where two great circles cross? Intersect their planes. (Want to walk a point along a great circle arc? Slerp from the start vector to the end vector). All in all, it's easier (for me) to conceptualise, and avoids a lot of trig for many operations. | |
| Feb 4, 2011 at 19:51 | comment | added | Kirk Kuykendall | @Dan - but with 3d coords, you'd need to densify in order to maintain constant elevation, wouldn't you? | |
| Feb 4, 2011 at 19:35 | comment | added | Dan S. | @Kirk: An easier-to-work-with representation (opinion here!) is to use orthographic 3D coordinates and represent the start/end points as vectors -- you're still using quaternions (to represent rotations in 3D) but they're much easier to think about. | |
| Feb 4, 2011 at 19:00 | comment | added | Kirk Kuykendall | I've worked with great circle line segments on a spheroid represented as a pole of rotation (point at lat/long) with a start angle, and end angle. I found it difficult to visualize the math used to manipulate them (quaternions). sciencedirect.com/… | |
| Feb 4, 2011 at 18:08 | history | edited | Dan S. | CC BY-SA 2.5 |
added 60 characters in body
|
| Feb 4, 2011 at 17:53 | comment | added | Dan S. | Nothing is exact with that interpretation of the word -- how about "parametric" instead as a better word choice? (Also, as a side note: if I restrict myself to spheroids rather than general ellipsoids, the parametric representations are somewhat less messy.) However, it's true that a lot of those things remain extremely messy/difficult --- hence my question! I'm not interested in a system which destroys existing data quality, but I don't feel a need to represent curves nobody is using either. | |
| Feb 4, 2011 at 15:46 | comment | added | whuber | Truly exact representations of any of these objects on any ellipsoid (which is not a sphere) is next to impossible. The geodesics are no longer portions of great circles in general; the rhumb lines will be nasty no matter what; geodesic circular arcs will be particularly messy. Is there really any point to doing this that is worth a couple of orders of magnitude of additional computation for every operation? | |
| Feb 4, 2011 at 2:16 | history | tweeted | twitter.com/#!/StackGIS/status/33348107274027008 | ||
| Feb 3, 2011 at 23:20 | history | asked | Dan S. | CC BY-SA 2.5 |