polyline arc from clockwise direction
Given two points and the tangent of an arc at one of the two points, the radius of the point is defined.
For example, to create the polyline with a straight line from 1 to 2 and an arc from 2 to 4 with a center at 5 do the following.
pline
tangent at 2 defined by the vector that goes from 2 to 3 do the following:
Command: PLINE
Specify start point: point-1
Current line-width is 0.0000
Specify next point or [Arc/Halfwidth/Length/Undo/Width]:point-2
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: a
Specify endpoint of arc (hold Ctrl to switch direction) or
[Angle/CEnter/CLose/Direction/Halfwidth/Line/Radius/Second pt/Undo/Width]: d
Specify the tangent direction for the start point of arc:point-3
Specify endpoint of the arc (hold Ctrl to switch direction):point-4
Specify endpoint of arc (hold Ctrl to switch direction) or
[Angle/CEnter/CLose/Direction/Halfwidth/Line/Radius/Second pt/Undo/Width]:[Enter]
The center of the arc is at the intersection of a line thru point-2 and perpendicular to line 2-3 (red line) and the perpendicular bisector of line 2-4 (yellow line). The radius of the arc is the distance from 2 to 5.
@john.taiariol wrote:
.... Is there an autocad command that will enable a clockwise arc in Polyline? (or simulate holding Ctrl key)
I may be misunderstanding somewhat, because I know nothing about NC code, what it's for, nor what the C3/C2 distinction is all about, but to answer that question:
Assuming you are automating drawing a Polyline, so you're in a (command "_.pline" ...) situation and it's already in Arc-segment mode, first feed in the Direction option, then this:
(* (/ (+ (getvar 'lastangle) pi) pi) 180)
and then give it the next point. That will start the arc segment off at the conversion to degrees of the reverse of the current tangent-continuation direction, which is what you get from holding the CTRL key when drawing one manually. [That also assumes that degrees are your current angular units setting. If not, convert in whatever way is appropriate to what the Pline command's Direction option wants to be told, or if that's radians, omit the conversion.]
@john.taiariol wrote:
I have a known radius so I prefer to create the polyline with start point, arc, radius [enter radius], at this point there is an option to change direction by holder the Ctrl Key. Can this be automated?
That one I don't know of a way to do. But I find a circumstance in doing it manually that you might not want. If the location of the cursor without CTRL held down will result in, let's say, a 1/4-circle arc segment going counterclockwise, with CTRL held down it doesn't give the mirror image of that [a quarter-circle going clockwise, which would be the result of changing the sign on the bulge factor in entity data], but rather the rest of the virtual circle of which that no-CTRL arc segment would be a part -- a 3/4-circle arc segment going clockwise. It doesn't seem possible to get any less-than-180-degree-swing arc segment that way [at least manually]. Could that possibly be a workable condition for your purposes?
What is the format of the "list of coordinates," and how are arc segments between them differentiated from line segments, and how is the radius stored in relation to the coordinates of the ends? Depending on the format, it might be possible to do this by something like a calculation of where the midpoint of the arc segment would be, and use of the Second-point option within Arc mode in a Polyline command.
@john.taiariol wrote:
The coordinates are in "X,Y" format and an arc is initiated with A,R [specify radius] and end point as shown below (single excel column):
249.891,225.708
A
R
35
266.455,196.305
L
266.494,192.339
A
R
50
250.398,155.089
....
Are the arc segments after the first one by any chance always tangent continuations from the line segments preceding them? If so, apart from the first one, you could just leave out the R's and the radius values that follow them, and just feed the rest into a PLINE command! But getting the first one would require some calculation to come up with a midpoint for the Second-point option, or a starting direction for the Direction option [can't think about that right now -- maybe later].
