Tangential Arc

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Tangential Arc

Postby apjjr » Mon Jan 19, 2009 1:35 am

How can I enter the End Angle on the command line for this type of arc?
Alex

v2.2.2.0 on WinXP and Ubuntu Linux 8.04
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Postby andrew » Mon Jan 19, 2009 9:30 am

- Move the mouse cursor to the side of the base entity at which the arc should be (there are two possibilities).
- QCAD places the relative zero point at the center of the arc you are about to draw.
- You can now enter a relative coordinate for the end point, e.g.:

Code: Select all
@1<-30


for an end angle of -30 degrees. Note that the radius of the relative coordinate should match about the radius of the arc, otherwise the side of the arc might change again since entering a coordinate has the same effect as moving and clicking the mouse.[/code]
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Postby apjjr » Mon Jan 19, 2009 9:28 pm

I want a radius of 1235 and 1 degree of arc. I type 'an', select the line, move the mouse to the side I want center on, press 'spacebar', enter '@1235<1' and QCAD draws an arc of a little more than 6.9778 degrees based on the length of the arc produced.
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Postby apjjr » Mon Jan 19, 2009 9:53 pm

Thanks, Andrew. I see what is going on, now. The angle is not relative to my start point. I started with a line going from lower left to upper right. I wanted an arc with a center 1235 to the upper left of that line. I understand now that the resulting arc is relative to QCAD's zero line, not the angle from the end of my starting line to the center of the arc. So, to get my angle, I subtract 90 from the angle of the line back to zero and subtract the angle of arc I want from that. I tried that and it worked. Whew! And that'll depend on which quadrant I'm in, too. This is for drawing land platts for real estate. I can make it work, but its a little awkward at this point. The information I start with is the length of the required arc, the radius and a line with which to be tangent. I calculate the angle for QCAD. I entered '@1230<-49.59' to get my 1 deg of arc. My starting line was at -140.59 deg. That would be 140.59-90-1=49.59.

- Alex
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Postby apjjr » Mon Jan 19, 2009 10:04 pm

Should I always use a radius a little less for the arc end point entry? i.e.; R=1235 so I enter @1230<-49.59.
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Postby apjjr » Tue Jan 20, 2009 11:45 pm

I'll experiment.

Thanks, Andrew and community, for a great CAD program.


Alex
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