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?