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OS: Windows 8 with QGIS 3.2

when attempting the following clip-by-mask exercise, the result works on 2.18 but not 3.2.

The data I am using is the QGIS training data with the Alaska Shapefile and the SR_50M_alskaa_nad.tif raster.

The Alaska shapefile needs cleanup before using as a mask and here are the steps followed:

  1. Load the Alaska shapefile
  2. Enable Check Geometry and Topology plugins
  3. Run Vector/Check Geometries
  4. Run Check Topology with no overlaps, no dups, and no gaps
  5. Run Grass/Vector/v.clean setting sliver to 10,000
  6. Load SR_50M_alaska_nad.tif
  7. Processing/Toolbox/GDAL/Raster Extraction/clip raster by a mask

The error message is GDAL command output:

Warning 1: Ring Self-intersection at or near point -2632521.5885887709 5137728.2501277877

ERROR 1: Cutline polygon is invalid.

Is there another cleanup tool I can run on this file in QGIS 3.2 to correct this issue?

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You already have the coordinates of the problem. Enter edit mode, copy paste the coordinates in the bottom part of the app and press enter to zoom there, and use the fix node tool to remove/move the node.

  • Thanks that did it. Here are the steps then: 1.Load the Alaska shapefile 2.Enable Check Geometry and Topology plugins 3.Run Vector/Check Geometries 4.Run Check Topology with no overlaps, no dups, and no gaps 5.Run Grass/Vector/v.clean setting sliver to 10,000 6.Run vector geometry/fix geometries 7.Load SR_50M_alaska_nad.tif 8.Processing/Toolbox/GDAL/Raster Extraction/clip raster by a mask – user127273 Aug 25 '18 at 14:35

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