filepro & maps

[ryan at bulldogsoftware.com]

On Thu, Nov 03, 2005 at 06:30:09PM -0600, Linda Hapner said:

> has anyone ever worked with a filepro database of GPS coordinates to develop a map?
> 
> We have the maps
> We have the data
> 
> need specific dots and number to be plotted on the maps based on the data.

What I have done in the past goes something like this:

1. Convert all coordinates to seconds. 
(Degrees x 3600) + (Minutes x 60) + Seconds.

2. Establish your origin in lat/long seconds.

3. Establish your extent in lat/long seconds.

4. Using 3 & 2 and your resolution, calculate your ratio of pixels per second
in both directions. Thats one ratio for latitude and another for
longitude.

Then given the target coordinates you will be able to approximate the
location on the map.

Remember that lines of longitude converge at the poles and therefore
the longitudinal ratio is only an approximation. There is a formula that
you can use but I don't have it handy. But for large-scale maps such
as an entire town it wouldn't be a factor.

-- 
Ryan Powers
Bulldog Software, Inc.
http://www.bulldogsoftware.com
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