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

[Hermann Peifer]

Charles,

Further below, you wrote:
 >>>>> Equal arc just means equal arc increments in latitude
 >>>>> and longitude.

Then your example 004VB41A.I23 comes with:
 >>>  Pixel Size = (0.000073242187500,-0.000044956841432)

To me, the above resolution doesn't look like equal increments in 
latitude and longitude. What am I missing here?

Hermann

On 2014-03-02 12:09, Charles Karney wrote:
> Got latitude and longitude switched!!  I should have said
>
> Products like CIB05 are equal arc with nominal resolution 5m x 5m.  What
> this means is that the latitude resolution is fixed at 0.000044956841432
> deg (about 5m) and the longitude resolution is fixed in each latitude
> "zone" to give roughly the same ground spacing.
>
> On 03/02/2014 06:04 AM, Charles Karney wrote:
>> I should have added.  See
>>
>> http://earth-info.nga.mil/publications/specs/printed/89041/89041.pdf
>>
>> 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
>>>>
>>>
>>
>
> _______________________________________________
> Proj mailing list
> Proj at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj
>