Perhaps I should clarify a bit what I meant, I haven't had any reactions
until now, positive or negative, and it is important for me.
I use Gdalwarp and gdaladdo extensively for goereferencing and tiling
large historical maps serieses (raster scans). To display them
efficiently, I need to create layers at different scale levels, e.g. if
the original maps have a pixel size of 10 meters, I need to resample
them to rasters with pixel sizes of 20, 40, 80 , 160, 320 and 640
meters, and tile all those maps appropriately. So the original maps have
to be resampled quite drastically. In Gdalwarp there is no adequeate
resampling algorithm, and you end up with very grainy map at those lower
resolutions. Gdaladdo has several more algorithms, with gauss in many
cases the most efficient. However, even with the gauss filter, maps
resampled at very low resolutions turn out too hazy. For an example see
the 1930 map of the Netherlands:
http://mapserver.sara.nl/topo/triang/
If you zoom in to more detailed levels, you'll see the way the image
sharpens. For the effect on black-white image choose the TMK-map (1850)
with the top-center button. Filters like "unsharp mask" would perform
much better in these cases.
So I would like to propose two enhancements to gdal:
- add additional filters to gdalwarp, gauss and the filters mentioned below.
- implement more filters for gdalwarp and gdaladdo, e.g. "unsharp mask",
or the "mode" filter asked by Jack below. Perhaps even add the
possibility to specify parameters, like in ImageMagick
I don't know how difficult is, and whether the gdal devs would find this
really an improvement for gdal. I could do this with some ImageMagick or
Gimp scripts, but it would be a kludge. As we are going to georeference
the complete cadastral and topographical map base of the Netherlands
from 1832 to 1994 the next few years (millions of map-scans), this
exentsion of gdal would come in very handy. And funding it will really
be no problem at all.
I would appreciate any kind of comment on this, positive or negative.
Regards,
Jan
Dr. J. Hartmann
Department of Geography
University of Amsterdam
On 03/27/2013 10:13 PM, John Twilley wrote:
I'm interested in this feature request as well. Adding the mode
resampling algorithm to gdalwarp would be very beneficial to my
projects, right up there with being able to access the warp API from
Python. Is this at all possible? Should I submit a feature request
on Trac, or what? Just let me know!
Jack.
--
mathuin at gmail dot com
On Mon, Feb 18, 2013 at 8:17 AM, Jan Hartmann <[email protected]
<mailto:[email protected]>> wrote:
Hi devs,
Would it be possible to add gauss and other interpolations to
gdalwarp? At the moment I georeference large scans to 2000*2000
tiles at the most detailed scale, and then create 2000*2000 tiles
at resolutions of 2, 4 6 etc times the original scale, using
gdaladdo and gauss or other interpolations. It would help
immensely if I could do that directly with gdalwarp.
Funding would probably no problem. The question is: can and should
it be done?
Jan
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