Bug report #15686

Save as Image from WMS/WMTS has reprojection issues

Added by whatnick - almost 4 years ago. Updated over 1 year ago.

Status:Closed
Priority:Normal
Assignee:whatnick -
Category:Rasters
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

Description

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.

test_no_reprojection.tif - Image saved with reprojection EPSG:3857 to EPSG:28354 (1.81 MB) whatnick -, 2016-10-10 12:29 AM

test_reprojection.tif - Image saved without reprojection in EPSG:3857 (1.29 MB) whatnick -, 2016-10-10 12:29 AM

History

#1 Updated by Martin Dobias almost 4 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.

#2 Updated by whatnick - almost 4 years ago

Reprojection was performed by selecting the target SRS in the "Save As" dialog. The resolution in both case was set to 0.08cm . The WMS we are using is private. I can create an account for you to debug and email the auth details to you.

#3 Updated by Giovanni Manghi over 3 years ago

  • Easy fix? set to No
  • Regression? set to No

#4 Updated by Jürgen Fischer about 3 years ago

  • Category set to Unknown

#5 Updated by whatnick - about 3 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.

#6 Updated by Giovanni Manghi about 3 years ago

  • Category changed from Unknown to Rasters

#7 Updated by whatnick - almost 3 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
OR
Chain GdalWarp API at the end of the save process to reproject instead of using the simple reprojector.

#8 Updated by Giovanni Manghi over 1 year ago

  • Resolution set to end of life
  • Status changed from Open to Closed

End of life notice: QGIS 2.18 LTR

Source:
http://blog.qgis.org/2019/03/09/end-of-life-notice-qgis-2-18-ltr/

QGIS 3.4 has recently become our new Long Term Release (LTR) version. This is a major step in our history – a long term release version based on the massive updates, library upgrades and improvements that we carried out in the course of the 2.x to 3x upgrade cycle.

We strongly encourage all users who are currently using QGIS 2.18 LTR as their preferred QGIS release to migrate to QGIS 3.4. This new LTR version will receive regular bugfixes for at least one year. It also includes hundreds of new functions, usability improvements, bugfixes, and other goodies. See the relevant changelogs for a good sampling of all the new features that have gone into version 3.4

Most plugins have been either migrated or incorporated into the core QGIS code base.

We strongly discourage the continued use of QGIS 2.18 LTR as it is now officially unsupported, which means we’ll not provide any bug fix releases for it.

You should also note that we intend to close all bug tickets referring to the now obsolete LTR version. Original reporters will receive a notification of the ticket closure and are encouraged to check whether the issue persists in the new LTR, in which case they should reopen the ticket.

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