[gdal-dev] re-gridding to a coarser grid

[Joaquim Luis]

Sorry for the noise that I introduced by mixing the GDAL and GMT's 
lists. I already replied to Andreas only because I though my message 
went only to him, but since it didn't here is a copy of it.

Joaquim

"
Andreas,
I'm very sorry but I sent that message to you by mistake as it was meant 
as a reply to another question in the GMT list. But since we are at it, 
your case is also probably better suite for GMT than GDAL. In GMT you 
have 'grdsample' to resample your grid or, if you really want to do 
things the correct way to avoid aliasing since you are going from high 
to lower resolution, 'grdfilter'.
Note that with GMT5 built with GDAL support you can read you grid 
directly but you are more limited on output formats (mostly netCDF).
"


> Andreas
>
> I think thats referring to my suggestion of GMT to do part of the work
>
>
>
>
>
>
> On Thu, 2011-12-15 at 14:00 +0100, Andreas H. wrote:
>> Joaquim,
>>
>>> nearneighbor is not really a good thing to use. Grid it with surface.
>> What do you mean by "grid it with surface"? In my GDAL (1.8.1), I only
>> have the following choices:
>>
>>     Available resampling methods:
>>         near (default), bilinear, cubic, cubicspline, lanczos.
>>
>> thanks for your insight,
>>
>> Andreas.
>>
>>> Joaquim
>>>
>>> Sent from my iPadiola
>>>
>>> On 14/12/2011, at 18:32, "Andreas H."<lists at hilboll.de>  wrote:
>>>
>>>> Travis,
>>>>
>>>> yes, thanks, I had already found that in the documentation. I'm just
>>>> wondering what e.g. 'bilinear' means when I go from a fine to a coarse
>>>> grid? If GDAL works in terms of "nodes", then I would assume 'bilinear'
>>>> means interpolation, which in turn would be a very different result from
>>>> working in terms of "cells" and then taking e.g. the average of all
>>>> "old" cells in the "new" grid.
>>>>
>>>> I hope you see my problem / question.
>>>>
>>>> Thanks for you insight,
>>>> Andreas.
>>>>
>>>> Am 14.12.2011 16:35, schrieb Travis Kirstine:
>>>>> Andreas,
>>>>>
>>>>> Yes gdalwarp support various resampling methods
>>>>>
>>>>> To use different resampling methods use the -r flag followed by the
>>>>> method
>>>>>
>>>>> eg
>>>>>
>>>>> gdalwarp -r near ..............
>>>>> gdalwarp -r bilinear .............
>>>>>
>>>>> etc...
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On 14 December 2011 08:26, Andreas H.<lists at hilboll.de>  wrote:
>>>>>> Travis,
>>>>>>
>>>>>> thanks for your answer!
>>>>>>
>>>>>> Regarding the resampling methods: Do they all just interpolate the
>>>>>> data? I
>>>>>> mean, when downsampling, usually I would use mean() or something
>>>>>> similar
>>>>>> to fill the new (coarser) grid cells. Doas gdalwarp actually do this
>>>>>> and
>>>>>> I'm not able to understand the documentation, or is it different?
>>>>>>
>>>>>> Thanks again!
>>>>>> Andreas.
>>>>>>
>>>>>>
>>>>>>> Andreas,
>>>>>>>
>>>>>>> gdalwarp can be used to resample images using the -tr flag or -ts
>>>>>>> flag.
>>>>>>>
>>>>>>> For example resample 1m image to 10m using cubic resampling and
>>>>>>> "target resolution'
>>>>>>>
>>>>>>> gdalwarp -r cubic -tr 10 10 input_1m.tif output_10m.tif
>>>>>>>
>>>>>>> You may have an issue determining the output resolution as I believe
>>>>>>> the resolution will be in decimal degrees rather than arc-seconds.
>>>>>>>
>>>>>>> Regards
>>>>>>>
>>>>>>> On 13 December 2011 14:52, Andreas H.<lists at hilboll.de>  wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> let's say I have a GeoTIFF file with a global grid in a 30
>>>>>>>> arc-second
>>>>>>>> resolution. Which would be the appropriate GDAL command to spatially
>>>>>>>> down-sample this file to say 0.125°?
>>>>>>>>
>>>>>>>> Thanks for your insight,
>>>>>>>> Andreas.
>>>>>>>> _______________________________________________
>>>>>>>> gdal-dev mailing list
>>>>>>>> gdal-dev at lists.osgeo.org
>>>>>>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>>>>
>>>>>> _______________________________________________
>>>>>> gdal-dev mailing list
>>>>>> gdal-dev at lists.osgeo.org
>>>>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>> _______________________________________________
>>>> gdal-dev mailing list
>>>> gdal-dev at lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>>
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>