I want to be able to calculate the longest edge of a rectangle polygon to create an expression for a style.

The styled rectangles will have variable orientations, widths and lengths.

I want to use this longest length to create an expression for the spacing of the Line Pattern Fill of the polygon style. The spacing will be set to 1/3 of the longest length of the polygon, so that the rectangle is visually divided into three segments (the rotation is already set to be -(main_angle($geometry))).

As an example, the distance of the longest edge is 3.501 m, which divided by three equals 1.167 m. This value (1.167 m) is set as my spacing. The effect is what I am after, I just want to automate this without manually calculating the 1/3 of the longest edge!

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1 Answer 1


Use this expression, and remember to set the units to Map Units and Clipping to Clip Lines Before Render.

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  • 1
    What version of QGIS is this solution for?
    – Cushen
    Commented May 30, 2023 at 2:27
  • @Cushen, 3.30 ‘s-Hertogenbosch.
    – Mayo
    Commented May 30, 2023 at 13:58

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