On Thu, Oct 6, 2011 at 10:27 AM, Ruth Garry <[email protected]> wrote: > Hi, > > We have GeoServer 2.0.0, providing raster background mapping for Great > Britain as a WMS service within an Intranet-based application. Maps are > delivered in GIF format. > > There is a problem with one layer - Ordnance Survey 1:250 000 Scale Colour > Raster GeoTIFFs. This data layer is made up of 56 source images and is > configured as a GeoServer ImageMosaic. There are 256 unique colours in the > source images. > > For some output maps in coastal areas, the white land (source image RGB is > 252,252,254) appears as exactly the same colour as the blue sea (source > image RGB is 228,240,254). It doesn't happen at all scales or for all map > extents and appears to more prevalent where image requests include or are > close to the edges of the input image tiles. Please see attached image for > an example. > > This only happens for map outputs in GIF or PNG8 formats, with JPEG and PNG > producing maps with distinct land and sea areas. PNG isn't an option for our > application for performance reasons. Changing to JPEG may be an option, but > we're still investigating this. > > Changing the WMS "Default Interpolation Option" from Bilinear to Nearest > Neighbour in GeoServer produces images with distinct land and sea areas, but > the image quality is too poor. > > I've also tried pre-processing the images to create overviews within the > GeoTIFFs using "gdaladdo". The gauss resampling algorithm resulted in images > with white land and blue sea for some of the source images when loaded into > GeoServer, but not others. (I tried using the other resampling algorithms > for gdaladdo, but all except gauss resulted in the blue map background on > the sample tile). > > The source images can be downloaded from the Ordnance Survey Open Data > website > (http://www.ordnancesurvey.co.uk/oswebsite/products/250k-raster/index.html).
Downloaded? As far as I can see one can download it after paying for it? > Any help on understanding on how the interpolation / conversion to GIF or > PNG8 is creating this effect gratefully received! I'd suggest you to use an external software to reduce the image to 256 colors (photoshop, irfanview, psp, gimp) and then save the result as a png or gif file, and then use it as the source for your custom palette: http://docs.geoserver.org/latest/en/user/tutorials/palettedimage/palettedimage.html Cheers Andrea -- ------------------------------------------------------- Ing. Andrea Aime GeoSolutions S.A.S. Tech lead Via Poggio alle Viti 1187 55054 Massarosa (LU) Italy phone: +39 0584 962313 fax: +39 0584 962313 http://www.geo-solutions.it http://geo-solutions.blogspot.com/ http://www.youtube.com/user/GeoSolutionsIT http://www.linkedin.com/in/andreaaime http://twitter.com/geowolf ------------------------------------------------------- ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity and more. Splunk takes this data and makes sense of it. Business sense. IT sense. Common sense. http://p.sf.net/sfu/splunk-d2dcopy1 _______________________________________________ Geoserver-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geoserver-users
