Re: [NTG-context] Metapost: directionpoint gives unexpected point(?)

Hi,

On 11 Feb 2021, at 17:41, Mikael Sundqvist wrote:

Thanks for your investigation and extended example!

So, if I understand it correctly, the problem occurs where the different circles are glued together with the .. construction.

Took me a while to get it, but the problem is the definition of p0: p[0] := cs .. cl .. (cs rotated 120) .. (cl rotated 120) .. (cs rotated 240) .. (cl rotated 240) .. cycle; Here are cs and cl after your earlier definition: cs := (141.73224999999996,-49.097491614210789) ..(75.312386775380347,111.25424516116959) ..(28.347427842053655,147.2925755432174); cl := (28.346108531095332,147.29283827977969) ..(0,154.88788322842163) ..(-28.346108531095332,147.29283827977969); Note how the last point of cs and the first point of cl are nearly the same. When you combine these bits into p0, p0 becomes a cyclic path with 18 points (where you really want/need only 12 points). The micro-segments between these nearly-identical paths are the problem. At smaller u values the differences between the points become zero, and the directionpoint of a path of length zero is mathematically undefined. I do not know a quick generic solution off hand, but that is what the issue is. Best wishes, Taco