Calculation of the distance between 2 coordinates of GPS in meters

Hello,

I have a project using a GPS module in my car e now I want to improve it adding a new option... I want to know if I am near of some known poitns as radars of speeds of the roads then I thought about calculating in the distance between known LA/LON of the current LAT/LON and to test if this value is greater that one determined ray, for example 30 meters.
As I want I covered an area relatively small I I thought about transforming degree, minute and seconds of the coordinates format of my gps ('$GPRMC,151805.812,A,2241.6835,S,04700.3015,W,0.0 0,,131206,,*1F ) in degrees and then to find the difference using the theorem of pitagoras: square shaped root of x^2+y^2, where x is lat1-lat2 and y is long1-long2. I have all datas in arrays (Lat var byte[9]: Lon var byte[10]).
To convert I think it: GRAUs = GRAUS+(MIN/60)+((.mmmm*60)/3600). Finally I multiply the value in degrees of the difference of the 2 coordinates for the value of 111120 meters (ray of the planet in the Equator), to only have an approach value. I also can search the accurate value of a degree in my region!
Somebody can help with some algorithm to only decide this problem using word and byte variables?

Thanks

Pimentel

Hello Pimentel,

You can use atan2 to find the angle heading from one lat/lon to another lat/lon coordinate. PicBasic doesn't include that math function, but you can use an assembly include file to perform a cordic equation for atan2. If you do a search on cordic in this forum, you will find one include for PIC16 devices, and one for PIC18 devices. There is also a trick to convert longitude to an adjusted value based on the cosine of current lat. I will explain a little more about this later.

Here is a link explaining how to use the PIC16 trig include file with lat/lon. In it you will find a link for the cordic trig include file thread.

http://www.picbasic.co.uk/forum/show...1216#post71216

-Walter