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I want to highlight the cloudfree pixels of a satellite image of which both of it with the cloudmask had been imported and reprojected from another GIS software.

Because of the reprojection, my cloudfree layer presents a small shift from the reprojected satellite image. The boundaries of my polygons are almost good but more importantly I have to correct the location of the clouds.

Advanced digitizing\Node Tool allows to select and apply a translation to the nodes of an inner ring but only through the use of a square-shaped selection tool. Oftentimes my clouds are so tightly close together and complexe that I cannot only select a single cloud with that tool (see picture below).

Anyone knows a way to easily just select all the nodes of an inner ring in QGIS?

enter image description here

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  • Do all of your inner polygones have the same offset? - In your picture, it looks like they all have been slightly shifted 4-5 pixel south? (I guess so, in case the offset was created by reprojecting the base data) If so, why don't you move the whole polygon (including the inner rings)?
    – Greg Z
    Commented Oct 13, 2016 at 12:51
  • Hi I forgot to mention that I need to get rid of cloudshades as well and the shift with their proper cloud might not be the same. Yes you're right the offset was indeed created by reprojection. However I can't just move the whole polygon since it will alter the whole topology with neighbouring polygons. Thanks anyway Commented Oct 13, 2016 at 13:46

2 Answers 2

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You can use the "Node Tool" in your Digitizing toolbar. Click on it, and select any vertex of your feature-to-edit. All vertices of this feature should now visualized by red boxes like this:

Select feature with Node Tool

Then draw a rectangle over your the vertices that should be manipulated (in your case, a inner ring):

Select nodes by rectangle

The vertices should now appear as selected (blue boxes): Selected nodes

Now you can click on one selected node an drag it - all of the other selected nodes should move too. And finally: drop it, where it should be placed!

result

UPDATE: you can also add single vertices / vertices in a rectangle to your selection by clicking on them / draw the rectangle while holding Cmd (on Mac, i guess Ctrl on Win). To remove one / a selection, just keep holding Cmd+Shift.

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  • I've already mentionned the Node tool in my question. The problem is the selection tool can only be a rectangle. Sometimes I've got to select an inner ring of more than 40 vertices and of a complex geometry. In this case a rectangle is really useless. Commented Oct 19, 2016 at 13:36
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Not an exact answer to your question, but OpenJUMP has a tool for you. Just click on the boundary of the inner ring with Select Linestrings.

enter image description here

OpenJUMP may have difficulties with satellite image background, though. If native support is not good enough installing GDAL extension should help.

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  • Hey thank you for your reply it would be great if the team behind QGIS could implement something like it. I don't know how reliable OpenJUMP can be with my data. However I do not want to import/export my data on too many different softwares. This tends to create lots of data distortion and unwanted artifacts. I assume I'll have to find a mean through some little programming and GDAL. Thanks anyway Commented Oct 13, 2016 at 14:44
  • If your mask is as shapefile there is no need to import/export. Just open, edit, and save. OpenJUMP is a reliable shapefile editor.
    – user30184
    Commented Oct 13, 2016 at 14:52

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