QGIS Angles – Calculating Polygon Main Angle Using QGIS: Detailed Method

anglesqgis

At the moment I have split my imported shapefile into the parts with the function 'qgis: explode' (pic1 & pic2):

Next I want to the polygon main angle of each "exploded" element.

In ArcGIS there is the function "Calculate Polygon Main Angle (Cartography)" which solves this problem, but I didn't find a suitable function for it in QGIS. "Calculate Polygon Main Angle (Cartography)" creates a new column in the. dbf file and fills it with the angles of each element.

Is there an equivalent function in QGIS?

Best Answer

QGIS has a main_angle(geometry) function since version 3.16: https://www.qgis.org/en/site/forusers/visualchangelog316/index.html#add-main-angle-function-to-return-the-estimated-main-angle-of-a-geometry

To calculate it you can use the expression main_angle($geometry) for a new field.

Be aware that it might return unexpected results or require further processing. See the GIF in the changelog (https://www.qgis.org/en/_images/87367553-aae7d680-c5be-11ea-923a-e81200f2b90c.gif) for an example.

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[GIS] How to measure angle in QGIS

http://anitagraser.com/2015/05/24/how-to-create-illuminated-contours-tanaka-style/ contains some way to do this:

First you split the lines/polygons into their atomic segments with v.split.

Then you calculate the azimuth for each of those features, see eg How to add Direction and Distance to attribute table? for the formula.

I don't know a better way but maybe there is.

PostGIS – Calculating Azimuth of Line Segments

Since you have extracted each individual line segment, you can directly compute their azimuth using their start and end points

CREATE VIEW attempt2 AS
  SELECT line_id, gid, geom,
         DEGREES(ST_Azimuth(st_startpoint(geom), st_endpoint(geom)))
  FROM   roads_exp;

Best Answer

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[GIS] How to measure angle in QGIS

PostGIS – Calculating Azimuth of Line Segments

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