QGIS TIN Interpolation

[@elliotscarffe2111]

What is the difference between idw and tin interpolation?

[@gisatup9675]

They are two different interpolation methods. IDW is based on distance, with the power function determining how much a point's influence changes with distance. It creates a smooth interpolation surface, with transitions between interpolated values generally not abrupt, unless the bull's eye effect is present. TIN is an interpolation method that uses Delaunay triangulation, with the average of 3 points used to determine values between them (think of the face of a triangle). Changes in values between these interpolated surfaces are abrupt.

[@elliotscarffe2111]

Thanks. I'm building contour lines to export to a tractor gps to follow. Is there a qgis function that allows you to create a line that follows a gradient? Like a contour line which has a percentage of fall?

[@gisatup9675]

@@elliotscarffe2111 I don't know of such a tool off hand but it sounds like a raster calculation function. If you can create a raster that accounts for the change in slope from a particular contour line and use that as a cost surface for LCPs, you might be able to do this.