Is there any tool in QGIS to select and translate an inner ring without altering it nor the rest of the polygon?

Question

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?

Answer 1

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:

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

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

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!

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.

Answer 2

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.

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