Re: Perl and Solving Trig/Converting GPS to x,y Cords

[roboticus]

in reply to Perl and Solving Trig/Converting GPS to x,y Cords

Pizentios:

It may not be quite that simple. Flat maps of spheres always have distortion. (Look up "spherical conformal mapping".) So circles on your map won't be the same as circles on the sphere. In addition, the type of projection used will affect the conversion of your planar coordinates to your spherical coordinates.

I'd suggest you find out what your error tolerances are, the largest distance you're going to be interested in, and what sorts of maps you'll be using.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[BrowserUk]

The Earth is round, but very big.

Between +70 and -70 degrees and distances under about 20 kilometers, bog standard 2D trig will produce results with errors less than 0.2%.

Between +-50 degs, it is less that 0.1%

[roboticus]

BrowserUk:

That may be true for all the practical cases for the OP, but it's not generally true. A trivial example being several of the polar maps. In those cases, the equator would give terrible results, and the center pole would give similarly good results.

For anyone interested, some really interesting stuff is at http://www.progonos.com/furuti/MapProj/Normal/TOC/cartTOC.html, especially the "Mathematics of Cartography" section.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[BrowserUk]

it's not generally true. A trivial example being several of the polar maps.

How many people are plotting GPS locations inside the artic/antartic circles?

Especially given that ionospheric signal path distortion renders GPS essentially unusable in those regions.