Re: world to xy

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Dave Freitag (dfreitag++at++fallschurch.esys.com)
Fri, 24 Oct 1997 12:42:57 -0400

> Garrett Williams wrote:
>
> does any one have the math for converting world coords to x,y coords
>
> Yes.
>
>
> easy question easy answer
>
> thanks for the help
>
> Sure.
>
>
> garrett

I am assuming worlds coord are Lat/Lons.

If this is the case than it is not an easy question.

A simple technique is to bound your scene against Lat/Long and
calculate degrees per pixel. For example you now your scene
is bounded by 34N118w 36N117W you calculate for each y unit will
represent 36 - 34 / max y units and for x, 118 - 117 / max x units.

To get more accurate results and for larger areas you may want to take into
account the curvature of the earth. All I can give on this is a Web Site which
talks about Map Projections and Geodetic Datums.

Check out this site: http://www.utexas.edu/depts/grg/gcraft/notes/gps/gps.html
Look for the icons Map Projections, Geodetic Datums and Coordinate systems.

Or you could use a realtime package which has database conversion such as
Paradigm's Vega.

Dave Freitag

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