# Point projection, tangent lines for draft block

Quick question…

How can I create a tangential projection of a curve in a draft block? If I have a curved line, how can project the end point so it creates a tangent with the end of the curve?

For example:

How can I project B9 so the line is tangent to the curve FC_si - B9 on B9?

Thanks!

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I’m not too sure what it is that you want to do. If you would like a node at the end of the arc from B9, then you can use the Segment an Arc tool with the arc length:

If this isn’t what you are trying to do, perhaps @Pneumarian will be able to help.

If I understand correctly you want a line that is tangent to the curve at B9? If it were an arc / circle that would be easy as you would know the center and can easily project a perpendicular of the center and B9. Given a spline I’m not sure… my geometry is a bit rusty.

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Assuming that you are using the term correctly, you want to do somewhat the opposite of the Curve with Control Points tool —to place a point in line with the control point.

As Douglas mentioned, in the case of an arc you just use the Point on Perpendicular tool, B9, center point, define length, decide whether to flip 180°, Done.

But in the case of a spline/“curve” what you do is use the “curve angles” category of “Input data” in the formula dialog:

• take your basic Point at Distance and Angle create a point using B9 as your base, (I suggest approximating its final location, for sanity, but it doesn’t really matter,)
• click the formula button on the angle field,
• select the “curve angles” category of “Input data,”
• type “b9” in the search field to make life easier,
• double-click the Angle1, or Angle2 option depending on whether B9 is at the start or finish of the spline, (make sure to delete the superfluous angle,)
• If you want your tangent going back along the line, you are done here. If you are wanting to extend the curve in a straight line, add 180°

I’m pretty sure you know what else to do to finish it off, judging by the content visible in your picture.

Happy drafting!

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That did it, thank you!

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