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I have straight lines in a metric CRS, connecting two points. So each line has exactly two vertices. I want to display these lines as curved arrows with curved labels above these arrows. QGIS version is 3.22.

To get the curved arrow, I am using geometry generator with a curved arrow on top of it. As expression I am using:

make_line(start_point($geometry), translate(centroid($geometry),length($geometry)/6,length($geometry)/6),end_point($geometry))

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But since this curved arrow is constructed via geometry generator, the label is still displayed on top of the actual line:

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Is there a way to define a rule for the label to follow the path from the curved arrow?

Note, that the line from geometry generator is actually not curved as shown below. So following this path would not be enough.

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I would really like to avoid creating new layers, but if there is absolutely no way to define a rule for the label to follow the arrow, I could also live with a solution that modifies the actual geometry to make smooth curves via PostGIS.

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A quite ok solution, but not perfect:

Use this expression for the symbology via geometry generator as well as for the label via geometry generator:

smooth(make_line(start_point($geometry),project(centroid($geometry),length($geometry)/6,radians(line_interpolate_angle($geometry,length($geometry)/2)+90)),end_point($geometry)),10)

Note the smooth() function. Play around with the number of iterations, to find a low number looking good.

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Resulting in a little offset:

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