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My goal is to know the angle in the intersection points between two linear shape using Qgis. (In the picture some of the "seems to be" ok results of the following procedure with the angle shown)

enter image description here

  1. I’ve extracted intersection points using “intersection lines tool”
  2. I’ve calculated the azimuth between linear shape 1 and intersection points
  3. I’ve calculated azimuth between linear shape 2 and intersection points. I used this expression to calculate azimuthes in the field calculator: degrees(azimuth(start_point($geometry), end_point($geometry)))
  4. I’ve than stored those values in each intersection point, and subtracted the first on the second, with module tool to get a positive value.

At this point something is obviously wrong in the procedure because some of the results are’nt visually correct (in the following example I'd expect an angle near 90)

enter image description here

Could you suggest a working method ?

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  • 2
    What map units are you using? Geographic coordinate systems (angular measurements) don't do well with plane trigonometry. Commented Aug 25 at 14:23
  • I use map units in meters, SR: EPSG:25832 - ETRS89. In the project properties SR listed are 25832 and 3003. I'm not sure why 3003 is present since all shapefiles are 25832. Commented Aug 25 at 14:30
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    Are your lines straight? Commented Aug 25 at 22:01
  • Lines are not straight. I thought that the angle would be calculated between vertex! So is the angle instead calculated between 0 and -1 ? This coud explain the partial expected results. I think I could create a buffer on vertex to clip the lines and repeat the procedure. What do you think? Commented Aug 26 at 6:09
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    or just decompose linear features to linear segments and repeat your procedure. Commented Aug 26 at 21:21

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