Find the intersection.
This function returns the intersection of two lines. Point1 and point2 represent the endpoints of the first line; point3 and point4 represent the endpoints of the second line. When the two lines intersect, the point of intersection is returned. If they do not intersect, nil is returned.
Flag is optional: if flag is not nil (T is typically used), the inters function performs as explained above. When flag is nil, the lines defined by the four points are considered infinite. Inters returns the point at which they eventually cross (unless they are parallel lines, in which case nil is returned).
Examples
| Code | Returns |
|---|---|
| (inters '(2 3) '(2 -4) '(4 1) '(0 1)) | (2 1) |
| (inters '(2 3) '(2 -4) '(4 1) '(3 1)) | nil |
| (inters '(2 3) '(2 -4) '(4 1) '(3 1) nil) | (2 1) |
| (inters '(2 3) '(2 -4) '(4 1) '(3 1) T) | nil |
| (inters '(1 1) '(3 1) '(1 0) '(3 0) nil) | nil |
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Programming Overview of LISP (LISt Processing) Language
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