i erroneously tried to calculate the intersection of a line with itself. it caused a segfault. (clear) (define l (build-line 2)) (with-primitive l (pdata-set "p" 0 (vector 0 -5 0)) (pdata-set "p" 1 (vector 3 5 0)) (line-intersect (pdata-ref "p" 0) (pdata-ref "p" 1))) best, gabor