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

Charles Karney charles.karney at sri.com
Sun Mar 2 06:04:18 EST 2014

I should have added.  See


for the specifications for CIB imagery data.

On 03/02/2014 06:02 AM, Charles Karney wrote:
> 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.
>    --Charles
> (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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