[Proj] Equal Arc Projection, GeoTIFF, and GDAL/Proj4

Charles Karney charles.karney at sri.com
Sun Mar 2 06:02:11 EST 2014

Products like CIB05 are equal arc with nominal resolution 5m x 5m.  What
this means is that the longitude resolution is fixed at
0.000044956841432 deg (about 5m) and the latitude resolution is fixed in
each latitude "zone" to give a roughly the same ground spacing.  For
example, 004VB41A.I23 is centered at 52d6'3.68"N, its resolution, is

   Pixel Size = (0.000073242187500,-0.000044956841432)

or about 5.015m x 5.002m.  The size of a CIB05 tile is about 7.5 km x
7.5km so this ground resolution is nearly constant across the image.

You can obviously do something similar if the requested resolution is
6m x 6m.


(On 03/02/2014 04:30 AM, Frederik Ramm wrote:
> Hi,
> On 02.03.2014 02:08, Charles Karney wrote:
>> Equal arc just means equal arc increments in latitude and longitude.  In
>> other words the projection is just ordinary longitude and latitude.
> Duh. That sounds a good deal simpler than I thought. Thank you.
> Am I then right in saying that a request like "I want an image in Equal
> Arc projection with a pixel size of 6 metres by 6 metres" does not make
> a lot of sense, since the width of a pixel will be constant in arc
> increments, and therefore not constant in metres?
> Bye
> Frederik

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