[postgis-devel] pgraster: st_resample error

[Bborie Park]

Tom,

I do have a question though.  Regardless of the transformed extent,
have you check the warped rasters to see if the data for a geographic
point is correct?  Correct being subjective as a warped raster is
resampled from the original raster to the new projection.

-bborie

On Fri, Dec 23, 2011 at 12:09 PM, Bborie Park <dustymugs at gmail.com> wrote:
> Disregard my last message.  I double-checked the scale-Y coming from
> ST_Resample versus that of gdalwarp and everything matches.  The drift
> is definitely coming from the projection string used in the warping.
> I'll have to ask the GDAL ML if I can pass a proj4 string instead of a
> WKT string.
>
> -bborie
>
> On Fri, Dec 23, 2011 at 8:01 AM, Bborie Park <dustymugs at gmail.com> wrote:
>> I plan on posting there after I do some experimenting.  The 20KM north
>> or south is probably coming from the plus or minus used for scale-Y.
>> I believe GDAL defaults to a negative value for scale-Y while PostGIS
>> Raster will use the scale-Y of the input raster.
>>
>> -bborie
>>
>> On Fri, Dec 23, 2011 at 7:58 AM, Tom van Tilburg
>> <tom.van.tilburg at gmail.com> wrote:
>>> Hi Bborie,
>>>
>>> thanks.
>>> I keep an eye on the ticket but it's a bit beyond my abilities to understand
>>> all of it ;-)
>>>
>>> My 2 cents however on Evens post:
>>>
>>> The errors in the amersfoort (28992) projecten have been known for a long
>>> time, that's not what bothers me at the moment.
>>>
>>> From all the small errors in the google-mercator projections (I think there
>>> are 4 around, all slightly different) I have never seen 20 km. error in the
>>> offset. It more feels to me that numbers have been swapped instead of
>>> miscalculated.
>>> The fact that postgis moves it 20 km south while gdal_warp moves it 20 km
>>> the opposite direction is also puzzling. What could that indicate?
>>>
>>> I'll keep an eye on the gdal list as well. Are you posting there?
>>>
>>> Cheers,
>>>  Tom
>>>
>>>
>>>
>>> On 23-12-2011 16:38, Bborie Park wrote:
>>>>
>>>> Tom,
>>>>
>>>> When you have the chance, can you look at ticket #1402?
>>>>
>>>> http://trac.osgeo.org/postgis/ticket/1402
>>>>
>>>> Even from the GDAL project responded with a thorough explanation of
>>>> what's causing the drift.  I'm still digesting his explanation and
>>>> will see what can be done to improve the projection handling in
>>>> PostGIS Raster.  Currently, we use the value in the "srtext" column of
>>>> spatial_ref_sys, but it looks like we may have better luck using the
>>>> "proj4text" column and have GDAL process it through their mechanisms.
>>>>
>>>> -bborie
>>>>
>>>>
>>>
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