[Proj] another simple coordinate conversion problem

Fischer, Robert P (GISS-6110)[COLUMBIA UNIVERSITY] robert.p.fischer-1 at nasa.gov
Mon Aug 13 21:06:58 EST 2012

Suppose you have a point A on the sphere, in regular (lat,lon) coordinates.  Let point N be your north pole, and P be your "new" north pole.

Compute the azimuthal distance from P to A.  This is your new latitude.  Look up the Haversine formula.

To get your new longitude: you will need to measure the angle between your line from P to A, versus some reference great circle.  I do not have the time to figure that one out right now.  But I'm sure a little research on Wikipedia can do it.  Remember that a great circle can be specified by the vector (point on the sphere) perpindicular to it.  For example, the equator is specified by the point at the north pole.

Proj.4 isn't really the appropriate tool for what you want.

-- Bob

From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org] On Behalf Of Martin Ivanov [martin.ivanov at ifg.uni-tuebingen.de]
Sent: Friday, August 10, 2012 9:16 AM
To: proj at lists.maptools.org
Subject: [Proj] another simple coordinate conversion problem

Dear users of PROJ,

I have a data set on a perfect sphere with radius 6371 km. The "projection"
is latitude-longitude, so the data practically are unprojected.

I need to convert the coordinates of the points in my data set from this
latlon projection to another latlon projection of the same sphere. The target
latlon projection is rotated, it has its north pole at 39.25 latitude and -162
longitude. Is there a way to make the conversion with proj?

Any suggestions will be appreciated.

Best regards,


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