DXF: Support spline paths for LEADER and MULTILEADER, and colors for LEADER
|Reported by:||Alan Thomas||Owned by:||Alan Thomas|
When a spline path is requested for a leader in a DXF file, we need to interpolate a cubic spline between those points with particular start and end tangents. This is accomplished by solving a linear system for the spline control points using a QR decomposition solver I wrote for another project (originally in C) some time ago. This isn't the speediest or cleanest implementation of cubic spline interpolation the world has ever seen, but being in an MIT-licensed environment places limits on the things that can be done by a non-expert, and in any case, efficiency is not really essential for a conversion tool like GDAL. Accuracy seems to be adequate for most purposes.
Additionally, I am adding support for DIMCLRD, which specifies the color of LEADER lines and arrowheads.