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Black 1px border around hillshade images
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Black 1px border around hillshade images
by Adam Ratcliffe-2
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I ran into a problem when warping my merged SRTM data that the output image was greater than the 4GB GeoTIFF file size limit. To overcome this problem I generated 2 output images, one for the North Island of New Zealand and the other for the South Island. I did this using the -te option to gdalwarp to specify the extents of the output file, color relief and hillshade images were generated from these warped images.
Problem is I'm seeing a dark band where the 2 sets of images meet, this can be seen in this screenshot: http://test.geosmart.co.nz/images/map-border.png Looking at the hillshade image there appears to be a black 1px border around the image. Could this be the source of the problem? Has anybody else seen and found a resolution for the issue? Cheers Adam Ratcliffe Software Developer GeoSmart PO Box 101001 29 Apollo Drive, Mairangi Bay, Auckland, NZ Ph: +64 9 9668757 Fx: +64 9 966 8721 Email: adam.ratcliffe@... Web: www.GeoSmart.co.nz SmartNAV - The premier Car Navigation dataset for NZ SmartFIND - Web and Mobile mapping solutions by GeoSmart www.aamaps.co.nz - For FREE web maps and directions within NZ Route2GO - Optimised journey planning to create the most efficient routes to your customers for your sales or service calls _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Matt Bartolome
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I had a similar issue with my nodata values on a particular geotiff set. I think I ended up setting -dstalpha to make it transparent. Not sure this would work for your case but worth a shot...
_______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Rahkonen Jukka
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Hi,
Is there some good reason for not creating a BigTIFF image and go over 4 GB limit? Gdal should do it automatically but sometimes it may need -co BIGTIFF=YES option. But naturally the 1 pixel border should have a more general solution. Have you tried to increase image size of both halfs by one pixel so they overlat at the seam? -Jukka Rahkonen- Adam Ratcliffe wrote: > I ran into a problem when warping my merged SRTM data that the output image was greater than the 4GB GeoTIFF file size limit. To overcome this problem I generated 2 output images, one for the North Island of New Zealand and the other for the South Island. I did this using the - te option to gdalwarp to specify the extents of the output file, color relief and hillshade images were generated from these warped images. > Problem is I'm seeing a dark band where the 2 sets of images meet, this can be seen in this screenshot: http://test.geosmart.co.nz/images/map-border.png Looking at the hillshade image there appears to be a black 1px border around the image. > Could this be the source of the problem? Has anybody else seen and found a resolution for the issue? > Cheers > Adam Ratcliffe Software Developer GeoSmart PO Box 101001 29 Apollo Drive, Mairangi Bay, Auckland, NZ Ph: +64 9 9668757 Fx: +64 9 966 8721 Email: adam.ratcliffe@... Web: www.GeoSmart.co.nz _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Adam Ratcliffe-2
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Hi Matt,
Thanks for the suggestion. I tried it but sadly does not seem to be a solution for my problem. I'm going to proceed with recompiling GDAL with support for BIGTIFF and doing it as one big image - I'll let the list know how I get on. Cheers Adam On 7/10/2009, at 3:00 PM, Matt Bartolome wrote:
Adam Ratcliffe Software Developer GeoSmart PO Box 101001 29 Apollo Drive, Mairangi Bay, Auckland, NZ Ph: +64 9 9668757 Fx: +64 9 966 8721 Email: adam.ratcliffe@... Web: www.GeoSmart.co.nz SmartNAV - The premier Car Navigation dataset for NZ SmartFIND - Web and Mobile mapping solutions by GeoSmart www.aamaps.co.nz - For FREE web maps and directions within NZ Route2GO - Optimised journey planning to create the most efficient routes to your customers for your sales or service calls _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Marcin Rudowski
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W dniu 07.10.2009 03:35, Adam Ratcliffe pisze:
> I ran into a problem when warping my merged SRTM data that the output > image was greater than the 4GB GeoTIFF file size limit. To overcome > this problem I generated 2 output images, one for the North Island of > New Zealand and the other for the South Island. I did this using the > -te option to gdalwarp to specify the extents of the output file, color > relief and hillshade images were generated from these warped images. > > Problem is I'm seeing a dark band where the 2 sets of images meet, this > can be seen in this > screenshot: http://test.geosmart.co.nz/images/map-border.png Looking at > the hillshade image there appears to be a black 1px border around the > image. > > Could this be the source of the problem? Has anybody else seen and > found a resolution for the issue? > When You are using hillshade rasters without composition, solution is pretty simple, just increase overlaping so that two adjacent tiffs has at least few px common area. hgt files already have such 1px overlaping, not sure how You merge them, but just in case add more. Problem also could be from misaligned resolution (-tr parameter in gdal_warp command), due to integer rounding of raster position. Using overlapping should fix black border in this case too, but some visible border could be still possible (misalignment). When -tr is set to exact power of 2 of output map resolution, at least rounding error will be the same for all points of rasters, and two adjacent rasters will join. I use tr value as described in mentioned earlier thread: http://www.nabble.com/My-patches-for-hill-shading-td22215531.html#a22799823 If using osm/google like zoom levels, it should be as one of: tr = 6378137*2*Pi/2^n where n is such, that tr is closest to Your desired resolution (90 is theoretical resolution of SRTM3, 30 for SRTM1). I use n=19 so tr = 76.437028295. This way one pixel of raster is one pixel of output image at zoom level 11 of google/osm projection/tiling scheme. It helps scaling on other zooms (just power of 2), and prevent different rounding errors for each raster (also helps with upscaling and adjacent output tiles alignment). So when warping from hgt's lat/lon projection to google/osm mercator projection I use: > gdalwarp -of GTiff -srcnodata 32767 -dstnodata 32767 -s_srs \ > "+proj=latlong +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 \ > +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over" \ > -t_srs "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 \ > +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over" \ > -rcs -order 3 -tr 76.437028295 76.437028295 -wt Float32 -ot Float32 \ > srtm.tif warped.tif I use -s_srs to override projection parameters from hgt format, to avoid ellipsoid reprojection, that gave me strange offset. srtm.tif is simply merge of some selected hgt files. Not sure, gdal should round them properly to raster resolution, however for tests with multiple rasters I used exact values to -te parameter due to problem described below. Use gdalinfo to check output tiff parameters: if pixel resolution matches (Pixel Size) and if there is enough overlapping(Corner Coordinates). If using composing effect, there is additional problem, that margin is not an option, rasters must meet without overlapping, to avoid double effect area. In this case rasters must be ideally joined (one edge end is another one start). Additionally I had to patch earlier mapnik, to avoid additional rounding problems (it's already committed): http://trac.mapnik.org/ticket/295 But in Your case it isn't necessary as described at the beginning. -- Marcin Rudowski _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Marcin Rudowski
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2009/10/7 Adam Ratcliffe <adam.ratcliffe@...>:
> Looking at the hillshade image there appears to be a black 1px border > around the image. > Could this be the source of the problem? Has anybody else seen and found a > resolution for the issue? Sorry, forget about that and this is the actual source of the problem. Way demtools works, it leaves black border on 2 edges of generated images (upper and left). Solution: add margin while merging and after demtool cut border with gdal (-te and probably gdal_translate). Use enough margin to have some overlapping after cutting edges, to avoid holes. My previous mail describes in fact situation of such holes or misalignment, when two rasters doesn't meet smoothly. -- Marcin Rudowski _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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Re: Black 1px border around hillshade images
by Adam Ratcliffe-2
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Thanks Marcin, that explains it. Will take the time to work through the other information you provided - sure to need it sooner or later.
Cheers Adam ________________________________________ From: Marcin Rudowski [mrudowski1@...] Sent: 07 October 2009 20:38 To: Adam Ratcliffe Cc: mapnik-users@... Subject: Re: [Mapnik-users] Black 1px border around hillshade images 2009/10/7 Adam Ratcliffe <adam.ratcliffe@...>: > Looking at the hillshade image there appears to be a black 1px border > around the image. > Could this be the source of the problem? Has anybody else seen and found a > resolution for the issue? Sorry, forget about that and this is the actual source of the problem. Way demtools works, it leaves black border on 2 edges of generated images (upper and left). Solution: add margin while merging and after demtool cut border with gdal (-te and probably gdal_translate). Use enough margin to have some overlapping after cutting edges, to avoid holes. My previous mail describes in fact situation of such holes or misalignment, when two rasters doesn't meet smoothly. -- Marcin Rudowski _______________________________________________ Mapnik-users mailing list Mapnik-users@... https://lists.berlios.de/mailman/listinfo/mapnik-users |
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