Contour Scanner And Trimmer

Mario Voigt

This tool helps you to find nasty contours which might bug you and prevent your work from being ready for production. It will find open contours, closed contours and self-intersecting contours. Self-intersecting contours can be closed or open contours so you can select this option additionally! Bentley-Ottmann algorithm is used to check for those intersections. The algorithm works with the accuracy of the selected paths (epsilons). Self-intersections usually happen if you just have large overlaps where the contour crosses itself like an 'eight' character for example. Using the highlighting it's easy to find contours with unproper path handles. While in a CAD system an area of of a surface can only be calculated if the contour is closed and clean, finding self intersections in InkScape is not required to do so. SVG format allows to calculate areas on open contours and self-twisted curves. This "artwork behaviour" makes it harder for handling machinery-like drawings for laser cutting, vinyl cutting or whatever. That's why we need to have extra sanity checks but we also have the great freedom of Inkscape. Finding self-intersecting contours does only work for curves with straight line segments (polylines) because it just calculates with a set of given XY points. It does not respect bezier curve segments. Bezier curves have no regular points but special handles, which define the slope of the curve per handle side (left and right). To properly handle a bezier curve we need to split the bezier curve in a lot of small linear segments (acting like infinitessimal solution). We can use the tool "Flatten Bezier to do this (will make your curve looking edgy or ugly possible). If you want to leave the shape of the line clean (bezier type, no edgy approximation) we can use Split Bezier (Subdivide) or Add Nodes instead. But remember that your calculated self-intersection points will only be an approximation then. The higher the subdivide count is the higher the precision of the calculated self-intersecting points coordinates will be.

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