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Calculating Lat/Lon for an X mile grid.
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Calculating Lat/Lon for an X mile grid. crgiles 05-19-2006
Posted by crgiles on May 19, 2006, 11:01 am
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 All, I've been charged with the task of generating a grid covering
certain states where each grid is X square miles.

To do this I need to take a point x1,y1 and add X mile(s) E/W and X
mile(s) N/S. Does anyone out there have a function that will accept a
point in lat/lon, a distance in miles, and a direction (N/S/E/W) only
and return a lat/lon of the new point?

tia,

CG


Posted by Uffe Kousgaard on May 19, 2006, 12:26 pm
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 http://williams.best.vwh.net/avform.htm#LL

Watch out, since ALL parameters need to be radians - also your X miles.

tc is the true course: 0, pi/2, pi and 3*pi/2 for the 4 directions.

> All, I've been charged with the task of generating a grid covering
> certain states where each grid is X square miles.
>
> To do this I need to take a point x1,y1 and add X mile(s) E/W and X
> mile(s) N/S. Does anyone out there have a function that will accept a
> point in lat/lon, a distance in miles, and a direction (N/S/E/W) only
> and return a lat/lon of the new point?
>
> tia,
>
> CG
>



Posted by ed_w on May 23, 2006, 12:05 pm
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What do you really want to do? It's not possible to overlay a square
grid on the surface of a sphere. Imagine trying to glue a piece of
plane graph paper onto a sphere. Somewhere it will develop creases, or
it will have to be stretched.
Many mid-western states have roads laid out on "section lines". Each
section encloses one square mile. The E-W roads run along parallels.
The N-S ones take periodic jogs. Without them, the sections would get
smaller in width as you went North.
The resulting sections are all (approximately one mile square, but
you'd need a loose definition of "grid" to describe the roads as such.
If a grid with curved sides is acceptable, lay out a square grid on
an equal area projection of the sphere (of which there are several) and
project back onto the sphere.

crgiles@gmail.com wrote:
> All, I've been charged with the task of generating a grid covering
> certain states where each grid is X square miles.
>
> To do this I need to take a point x1,y1 and add X mile(s) E/W and X
> mile(s) N/S. Does anyone out there have a function that will accept a
> point in lat/lon, a distance in miles, and a direction (N/S/E/W) only
> and return a lat/lon of the new point?
>
> tia,
>
> CG


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