Bug report #15686
Save as Image from WMS/WMTS has reprojection issues
|Affected QGIS version:||2.16.3||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:||end of life|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||23609|
When saving images from WMS/WMTS to a projection not native to the source online dataset, reprojection is performed and artefacts are introduced. See attached sample images for a demonstration.
#1 Updated by Martin Dobias almost 5 years ago
How did you do the export with and without reprojection? Do you have source WMS/WMTS to replicate it?
Anyway, it can be expected that some artifacts are introduced, especially if the attached reprojected image has slightly smaller resolution than the original layer.
#5 Updated by whatnick - almost 4 years ago
We currently have a work around chaining the WMS Save-As with Raster tools (GDAL) warp - https://metromap.freshdesk.com/support/solutions/articles/22000000726--using . I have some time to do dev work and will submit pull requests over the next month, should be a relatively benign fix since reprojection is in place already just interpolation algorithms are not selectable.
#7 Updated by whatnick - almost 4 years ago
- Assignee set to whatnick -
The issue is mainly due to "core\raster\qgsrasterprojector.cpp" performing fast/approximate raster reprojection meant for on-the-fly reprojection for saving high-quality files to disk. I propose the following enhancements:
1) Add check-box in Save As Dialog for WMS to trigger alternate resampling methods
2) Rewrite raster reprojector to respect this flag and implement at least bilinear resampling
Chain GdalWarp API at the end of the save process to reproject instead of using the simple reprojector.
#8 Updated by Giovanni Manghi over 2 years ago
- Resolution set to end of life
- Status changed from Open to Closed
End of life notice: QGIS 2.18 LTR
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