AutoCAD 2010/2011/2012 DWG Format

[#1]

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azrdgldr wrote:

You want it snap to a point that doesn't exist (persay) according to the drawing database.  You want to pick to an intersection of line to an invisible extention of the arC right?  You can't do that,

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I don't believe it has anything to do with whether the point exists in the database because the  "Apparent Intersection" OSnap works fine with arcs.  AutoCAD also has no trouble Trimming or Extending to the extension of arcs when  EDGEMODE is enabled. Similarly, the "Extension" OSnap gives visual proof that AutoCAD would have no trouble finding the Perp extension of an arc, yet it doesn't  (see link below)  Snapping to the line to the arc center and then trimming with Edgmode1 or grip editing the new line back to the "Apparent Intersection" are probably the two fastest work-a-rounds.

http://www.screencast.com/t/XTbFRaWRwMKT

[#2]

This post is talking about straight snaping perp to an arc and not an apparent intersection.  For apparent intersection, the line and arc must pre-exist.  It helps if you read the whole post to know what the problem is, so you can chime in with a solution.  Know what the actual conversation is about before adding your two cents worth.

[#3]

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azrdgldr wrote:

This post is talking about straight snaping perp to an arc and not an apparent intersection. 

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This thread is not about "straight snapping" perp to an arc.  The OP is asking why Perp OSnap won't  acquire Perpendicularity at the extension of an arc, just as it does for lines.  Whether that missing functionality is an oversite, a bug, or an conscience decision, is yet to be determined,  but it's not a geometrical, mathmatical, or computational limitation because other commands and other OSnaps will lock onto arc extensions, even when used in conjunction with other OSnaps and/or tracking modes. 

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azrdgldr wrote:
It helps if you read the whole post to know what the problem is, so you can chime in with a solution.  Know what the actual conversation is about before adding your two cents worth.

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That seems incredibly rude, presumptuous, and condescending, but non-the-less, you're quite mistaken that I didn't read the entire thread, that I don't understand the situation, and my reply was never intended to be a "solution" rather it was demonstration that AutoCAD is perfectly capable of acquiring points beyond the defined endpoints of arc, despite the fact the Perp and Tan OSnaps currently do not.

Geometric constrainst are yet another example where AutoCAD can establish, and maintain Perpendicularity and Tangency between arcs (including their extensions) and other objects with only one "fixed point" as would be the case when trying to snap a line Perpendicular to the extension of an arc. Again it's not a question of why AutoCAD can't do it, because AutoCAD clearly can, the question is why the developers didn't include it.

[#4]

Stevev0983 wrote

"By definition, a line cannot be perpendicular to an arc since perpendicular means to meet at right angles. It can only be perpendicular to another line or a plane (and actually, the correct term for a line and a plane is "normal", not perpendicular). Not sure why ACAD ever lights up the perp marker even when you extend the arc."

Sorry hate to correct you. You can have a point that is perpendicular to an arc whether outisde or inside the arc. It is perpendicular to the tangent of that point on the arc. Which you did get correct perpendicular is at right angles.

[#5]

Stevev0983 wrote

"By definition, a line cannot be perpendicular to an arc since perpendicular means to meet at right angles. It can only be perpendicular to another line or a plane (and actually, the correct term for a line and a plane is "normal", not perpendicular). Not sure why ACAD ever lights up the perp marker even when you extend the arc."

Sorry hate to correct you. You can have a point that is perpendicular to an arc whether outisde or inside the arc. It is perpendicular to the tangent of that point on the arc. Which you did get correct perpendicular is at right angles.