[sac-forum] Re: Determining Position

The problem with that is, while you are correct about not worrying about the
curvature of earth over a short distance, you do need to factor in the fact
that the meridians (Y axis) are not parallel. A GPS unit can easily do what
you are looking for. Also, there is a small freeware app called
Forward-Inverse that can figure these things out :
www.mentorsoftwareinc.com/PRODUCTS/FWDINV.HTM 

It would be a two step process. As an example you want to find the mid point
of a line between Cherry Road (N34 31.157, W 112 5.102 & 5 Mile Meadow (N 34
41.975, W 111 26.814). 

Step 1. Determine the Bearing & Distance between the two points. One could
either punch both points into a GPSr and get the Bearing & Distance or using
The app mentioned above enter the coords directly & get the same answer
(without wasting GPSr Batteries). I get the following:  Azimuth 70Deg 57.1
Min, 38.43 Miles.

Step two: Project a waypoint from the origin 1/2 the distance. In this case,
70Deg 57.1, for 19.215 Miles. Using Forward-Inverse I get N34 36.591, W111
45.980. Again you can do this from a GPS receiver as well.

If you really want to try this on graph paper, you'd be best to convert
positions to UTM Coordinates, which is a rectilinear system based on the
metric system. I won't get into that here. 

Hope this helps

Rick Tejera 
President 
Editor SACnews
Saguaro Astronomy Club
Phoenix, Arizona
saguaroastro@xxxxxxx
www.saguaroastro.org


-----Original Message-----
From: sac-forum-bounce@xxxxxxxxxxxxx [mailto:sac-forum-bounce@xxxxxxxxxxxxx]
On Behalf Of Stan Gorodenski
Sent: Thursday, May 18, 2006 9:02 PM
To: sac-forum@xxxxxxxxxxxxx
Subject: [sac-forum] Re: Determining Position

Since I am always thinking about something like this, it just occurred to me
a way I could do it. I have plenty of old style graph paper, fine divisioned
and some large sheets. I could set up x & y coordinates, one for latitude
and the other for longitude, plot the two points, and then draw a straight
line between the two and read off latituded and longitude for the points in
between. Or, and probably the best, it should be easy to get a slope for a
straight line just by the theory of a regression line. For my purpose, I do
not need to take into account the earth curvature since any deviation would
undoubtedly be much smaller than the accuracy of a GPS - After getting the
in between points I plan to go out to the field and locate them using a GPS.
Stan

Stan Gorodenski wrote:

> Assume I have the latitude and longitude of two points separated by a 
> thousand feet. I want to find the mid point on a straight line between 
> the two, or for that matter, anywhere along the straight line. There 
> are trees between the two points so that they cannot be seen. What is 
> the best way to do this? Is there an easy way to do it with the GPS 
> units?
> Stan
>
>
>

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