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I wish to add a break line to an interpolation of a set of survey points to simulate an elevated ridge in the survey area. Using QGIS 2.6 on Windows 7.

I have created a polyline shapefile with a numeric field for the z attribute, and have included this field in the interpolation with type set to break lines (see screenshot), however the interpolation ignores the break line.

What confuses me is that the interpolation works fine with the point elevation which is also an explicit field (i.e. you have to tell the interpolation to use) but not the break line.

Do I need to create a true 3D polyline to use as the break line, and if so can I do this in QGIS?

breakline screenshot

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    I never managed to get break lines work as well and therefore haven't tried for while. But while thinking about it, maybe it would make sense to convert your break line to points and merge them with your elevation points layer. Before converting, densify the number of points in the lines with the densify function in the toolbox, so you will have points at a chosen distance and not only the vertices at corners. This will definately not "cut" like a break line, but maybe enhance the output a bit. – Bernd V. Mar 11 '15 at 14:22
  • A BL should not be crossed by triangles' edges. Thus, converting the line to points is not a good idea imho. – s.k Sep 23 '16 at 21:19

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