Re: [OpenMap Users] projection problem

From: duboscqd <duboscqd_at_wanadoo.fr>
Date: Sun, 9 Mar 2008 07:08:45 +0100

Hello again,

A few precisions on my question :
the point i'm looking for is defined as follow :
if X = 0 (0 north) the point P1 should have the same latitude as the reference point
if y = 0 (west) the point should have the same longitude as the reference point
My problem is to find the longitude Lon1 of a point that has the same latitude as the reference and is X meters west from the reference
and to find the latitude lat1of a point that has the same longitude as the reference and is Y meters north from the reference.
My point is (Lat1, Lon1)


An exemple : my reference point is 43N006E, and the point i'm looking for is 585 miles east and 60 miles north.
If I try graphically with the distance tool of OPENMAP,
when i point 585 miles east of my reference with an angle of -90° i find (about) 42,4N.
I assume <<ref.getPoint( rads , angle );>> use a +/- 90 angle to go east and west
(at least it seems according to my differents tries)

In that example, for <<ref.getPoint>>, the angle i should use to find my point should be about -86° that gives a point
585 miles east with the same latitude (43N),
of course that angle depends on the distance and i don't know how to find it.

Can i do that with a few calls using existing openmap methods ?

  ----- Original Message -----
  From: duboscqd
  To: openmap-users_at_bbn.com
  Sent: Saturday, March 08, 2008 9:33 AM
  Subject: [OpenMap Users] projection problem


  Hello,

  I would lile to interpret & display data that comes as follow :
  - I receive a reference point with lat/lon data
  - i receive points (let say P1) that is expressed with X (miles or meters) and Y(miles or meters) distance from the reference point.
  The sender gives X and Y according to a flat representation centered on the reference point.

  To get the lat/lon of P1 i compute distance (rads) and angle from X and Y then use : ref.getPoint( rads , angle );

  However the result is not clean, since it seems that the "getPoint call" computes the lat/lon taking into considerations that the distance is on the earth,
  and in my case the distance is from the flat representation.

  I hope my explanantions are clear enough.
  Is there any other transformation method i could use to solve that problem ?

  Thx by advance


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Received on Tue Mar 11 2008 - 01:00:48 EDT

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