On mercredi 19 août 2020 18:41:51 CEST Stephen Woodbridge wrote: > Hi all, > > I've been puzzling over a problem with trying to get a higher resolution > images using a VRT file so low res data looks smoother in mapserver. > > This is my source tif image: > > gdalinfo /maps/wms/data/HYCOM/HYCOM_today_mlt.tif > Driver: GTiff/GeoTIFF > Files: /maps/wms/data/HYCOM/HYCOM_today_mlt.tif > Size is 4500, 4251 > Coordinate System is: > GEOGCS["WGS 84", > DATUM["WGS_1984", > SPHEROID["WGS 84",6378137,298.257223563, > AUTHORITY["EPSG","7030"]], > AUTHORITY["EPSG","6326"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4326"]] > Origin = (-180.000000000000000,90.000000000000000) > Pixel Size = (0.080000000000000,-0.040000000000000) > Metadata: > AREA_OR_POINT=Area > [snip more metadata] > Image Structure Metadata: > INTERLEAVE=BAND > Corner Coordinates: > Upper Left (-180.0000000, 90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N) > Lower Left (-180.0000000, -80.0400000) (180d 0' 0.00"W, 80d 2'24.00"S) > Upper Right ( 180.0000000, 90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N) > Lower Right ( 180.0000000, -80.0400000) (180d 0' 0.00"E, 80d 2'24.00"S) > Center ( 0.0000000, 4.9800000) ( 0d 0' 0.01"E, 4d58'48.00"N) > Band 1 Block=4500x1 Type=Float32, ColorInterp=Gray > NoData Value=1.2676506002282294e+30 > Overviews: 2250x2126, 1125x1063, 563x532, 282x266, 141x133, 71x67 > > > I generate a VRT file as part of my processing and add a color table and > increase the resolution. It looks like this: > > gdalinfo /maps/wms/data/HYCOM/HYCOM_today_mlt.vrt > Driver: VRT/Virtual Raster > Files: /maps/wms/data/HYCOM/HYCOM_today_mlt.vrt > /maps/wms/data/HYCOM/HYCOM_today_mlt.tif > Size is 72000, 68016 > Coordinate System is: > GEOGCS["WGS 84", > DATUM["WGS_1984", > SPHEROID["WGS 84",6378137,298.257223563, > AUTHORITY["EPSG","7030"]], > AUTHORITY["EPSG","6326"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4326"]] > Origin = (-180.000000000000000,90.000000000000000) > Pixel Size = (0.005000000000000,-0.002500000000000) > Corner Coordinates: > Upper Left (-180.0000000, 90.0000000) (180d 0' 0.00"W, 90d 0' 0.00"N) > Lower Left (-180.0000000, -80.0400000) (180d 0' 0.00"W, 80d 2'24.00"S) > Upper Right ( 180.0000000, 90.0000000) (180d 0' 0.00"E, 90d 0' 0.00"N) > Lower Right ( 180.0000000, -80.0400000) (180d 0' 0.00"E, 80d 2'24.00"S) > Center ( 0.0000000, 4.9800000) ( 0d 0' 0.01"E, 4d58'48.00"N) > Band 1 Block=128x128 Type=Byte, ColorInterp=Palette > Overviews: 36000x34016, 18000x17008, 9008x8512, 4512x4256, 2256x2128, > 1136x1072 > Color Table (RGB with 256 entries) > [snip color table] > > > And in my mapfile I have a layer defined like: > > LAYER > NAME "mlt" > STATUS ON > TYPE RASTER > PROJECTION "init=epsg:4326" END > DATA "/maps/wms/data/HYCOM/HYCOM_today_mlt.vrt" > PROCESSING "NODATA=1.2676506002282294e+30" > PROCESSING "SCALE=0,250" > END > > This all seems like it should be working correctly, but in my OL app, > the resolution is not changing. I would expect the with the higher > resolution I would see smoother color transitions as I zoom in on the > image and that the pixel blocks would appear smaller. Unfortunately, I'm > not seeing a difference. > > So I assume I've done something wrong somewhere, but I'm not see what :(
By default, VRT uses nearest resampling. You must specify something else. Look for "A resampling attribute can be specified" in https://gdal.org/drivers/raster/vrt.html Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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