Tangency Point

This construction generates a point at which a tangent line from a specified reference point meets a specified arc, circle or ellipse.

Examples

1. NEW STRA

   FPT X100 Y100

   TPT X300 Y200 TAN @

   

   Figure 20:12. Use of the TANGENCY Point Construction

   This STRA element has an explicit FPT; its TPT is the point on the ARC that, together with (X300, Y200), forms a tangent to the ARC. Here the cursor hit acts as a qualifying point. Notice that the STRA produced here is not a tangent line.

2. NEW STRA

   FPT X200 Y100

   TPT X200 Y100 TAN PREV CIRC QUAL @

   Here, the STRA has one endpoint defined explicitly and the other defined as the point where the tangent line through (X200, Y100) intersects the previous CIRC in list order which is closest to the cursor-specified qualifying point.

   

   Figure 20:13. Use of the TANGENT Construction to give a Tangential Line

   The qualifier is necessary since in this case there are two possible tangents. (Other tangent shown dashed.) Other cases would not need a qualifier since only one tangent would be possible (see below).

   

3. NEW STRA DEF @ @ TAN @

   In this case, the first cursor hit defines one endpoint of the STRA, the second defines one end of a tangent, and the third picks the circle and also acts as a qualifier. The resulting STRA intersects the tangent. See below.

Figure 20:14. Use of the TANGENT Construction to give a Line perpendicular to a Tangent