Help with code to convert latitude longitude coordonates to cartesian and then back again

[jserafy]

Hi:

I've read it is improper to average a series of latitude-longitude coordinates without first converting to Cartesian coordinates.

If someone could provide sas code to process the example data below, I'd appreciate it. 

-----------------

data a; input location lat lon;
cards;
1  27.7970   -93.6191
2  28.0290 -93.6310
3  28.3661  -91.1429
;

*Code to convert above spherical coordinates to Cartesian coordinates;

proc print; var location cart_lat cart_lon; run;

* Code to convert the Cartesian coordinates back to spherical coordinates;
proc print; var location lat lon; run;

[ballardw]

Purpose?

How large of a geographic region are you dealing with? For most purposes if the area is less than several hundred square miles or kilometers the lat/long behave like Cartesian coordinates for most purposes.