GPS Points in Lat & Long to coordinates & distances?

[jheidt2543]

I have the Lat. & Long. for six points on a site taken with a hand held GPS unit. I would like to convert these to coordinates so I can compute the lenghts between points. I am looking for the equations or a reference, any help would be appreciated. I don't need a high degree of accuracy or precision, I am making a rough map of my deer hunting stands.

Thanks in advance.

 

[AllenS]

Try Freeware Corpscon from the NGS website.

 

[flamby]

Assuming,

Latitude=theta
Longitude=alpha
at one point.
And assuming perfectly circular earth,

Radius r(at this lat) = R cos(theta), where R rad of earth at equator

Then you can convert your lat/long to cartesian X,Y

X=r*alpha;
Y=R*theta;

(all angles in radians only)

Thereafter it is easy for you to plot these x,y's on a plane.

For an elliptical shape of earth, the expression r=R*cos(theta) will modify, but I hope you will not need it.

 

[carlorom]

I know this is a bit late but the answer given for this question is the most basic and dangerous.

Lat Long by GPS is based on Ellipsoidal approximations of the earth's surface.

Usually GPS receivers get positions on WGS84. There are standard fromulas available to convert to Y-X-Z ie cartesian co-ordinates from the basic Lat Long these are defined off standard meridians and usually distance from the equator etc.

To complicate matters further each country has adopted a standard ellipsoid which is not necessarilly WGS84 but some other system eg. Clarke 1880, UTM transverse mercator, Cape system, etc. Conversions from GPS Lat Long must hence be done using MOLODENSKY adjustments- It is way too complicated to explain here and I suggest you look into MOLODENSKY web searches. There are shareware and commercial packages available which will help but be careful how you use them - what accuracy you require etc. In South Africa there is a very good package available from the Universtiy of Cape Town known as Xform with excellent explanations.

Also most good GPS receiver manuals will give some conversions or point you in the right direction.

 

[flamby]

carlorom,
Most basic- yes, but dangerous?
We have already discussed that high precision was not needed in this case of "deer hunting stands" and having clarified that I assumed earth is circular (which it is not as all here know), I hope I was not far removed from what jheidt2543 was looking for.
Regards,
flame

 

[jheidt2543]

Thanks to all for the input! All I was looking for was an approximation of the distances, I don't need surveying type precision in this instance. However, it is nice to know that my simple problem is solved and where to look if I need a more precise answer.

Thanks again!