Dan S.
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 Feb 28 awarded Good Answer Aug 13 awarded Yearling Sep 24 awarded Autobiographer Sep 23 awarded Nice Answer Aug 12 awarded Yearling May 29 awarded Nice Answer Dec 29 awarded Popular Question Aug 13 awarded Yearling Mar 18 awarded Nice Answer Aug 12 awarded Yearling Jun 8 awarded Caucus Aug 13 awarded Yearling Jul 21 comment What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation? Here goes, as concisely as I could make it. My reasoning is expressed in 3D Cartesian, not angular coords: (a) On a sphere, all points in a great circle are coplanar. (b) The transformation to the auxiliary sphere is linear and invertible. (Mistaken thinking?) (c) All points in an elliptical geodesic transform to points along a great circle on the aux. sphere. (d) All points on an elliptical geodesic are coplanar as well, due to (b). Finally, (e): Due to coplanarity, two candidate geodesic intersection points on the ellipsoid can be found by plane intersection. Jul 21 comment What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation? I'm quite sure I'm off track, but not sure where; I'd love it if you could help debug my reasoning. (Next comment.) Otherwise: thanks a heap for the helpful code + commentary + link; it's tremendously useful. Jul 20 comment What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation? A belated thanks for this reply. :) I'm too underwater to do more than skim at the moment, but it looks to be a a quite fantastic trove. A quick note on geodesic intersections since you called them out -- mostly for you to review as a check on my own undercaffinated intuition: Exact intersections of spherical geodesics can be found easily by intersecting the planes of the corresponding great circles, and that result carries over to ellipsoids by using an auxiliary sphere -- or am I missing something there? Apr 14 comment what is the best way to programmatically convert between WKT and Proj4 string? After some googling: spatialreference.org is powered by GDAL as well & uses the same code path (more or less), it seems. Apr 13 comment Interpolate points between coordinates for smooth animation in google maps or openmap @Kirk -- an library would make more sense than a web service. If smooth animation is your goal, you want to interpolate as quickly as the view can be updated. (And by no coincidence, libraries that support animation like jQuery already have interpolation & easing built in....) Apr 12 comment Convert x, y position in georeferenced image (with world file) to longitude, latitude? @antonj -- that's the EPSG code for the projection MerseyViking is using, which incidentally is not the same one as in your question. (Frequently used projections have a code assigned to them by the EPSG. I bet yours has an EPSG code too, but it wasn't included in the .prj). Apr 12 comment Convert x, y position in georeferenced image (with world file) to longitude, latitude? @antonj -- It's just the lazy (and web-linkable) way I used to convert your .prj parameters into proj4j arguments. The site gives you lots of ways to download a spatial reference, but the "proj4" link is the one you care about. They're all the same spatial reference info, just different formats. E.g. the "Lambert Azimuthal Equal-Area" in your .prj translates directly into the `+proj=laea` argument on the "proj4" version; the "central-meridian" of 20 translates to `+lon_0=20`, etc. Apr 12 comment Convert x, y position in georeferenced image (with world file) to longitude, latitude? Upon a closer read, I'm not certain your +0.5 is correct. (See the comment I left in the discussion on the main question.)