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Re: Finding coordinates on the circumference of a circle [message #44819]

Tue, 19 July 2005 15:21

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

guillaume.drolet.1@ulaval.ca wrote:
> Thanks a lot for helping me with this.
>
> This last suggestion with MAP_PROJ is great, although I don't quite
> understand everything. For example, do you specify the radius in meters
> because the Azimuthal Equidistant projection is in meters?

The default SPHERE_RADIUS is the true radius of the Earth in meters.
Therefore, radial distances in the Azimuthal Equidistant projection
will also be in meters. This depends upon knowing precisely how the map
projection works.

If you're not sure about the scale being used in a given projection,
select two points where you know:

a) what the true distance between those points is and
b) that the projection you're using preserves that distance.

Pass those points to MAP_PROJ_FORWARD, and from the results you can
calculate the scale factor being used, rather than guessing what it is.

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[Message index]

		Re: Finding coordinates on the circumference of a circle By: James Kuyper on Tue, 19 July 2005 15:21
		Re: Finding coordinates on the circumference of a circle By: guillaume.drolet.1 on Tue, 19 July 2005 12:13
		Re: Finding coordinates on the circumference of a circle By: James Kuyper on Tue, 19 July 2005 10:10
		Re: Finding coordinates on the circumference of a circle By: K. Bowman on Tue, 19 July 2005 08:11

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