How to draw arc with three points

[qiucx]

Now, i have the start, end point of arc and any other point in arc, and then, i need an algorithm to draw this arc. Does anyone has similar algorithm?

From my understanding, we need to calculate the center point (the cross of two lines which is vertical with line [start point+other point] and [end point + other point]) and radius (the distance of center point and start point), it is a bit complex and i have no idea about next steps.

I appreciate your reply. thanks

[TIG]

I have posted some Arc plugins to do this.
I think Didier Bur did something similar at the crai Dept ?

[mozzie]

TIG's Arc 3 points does this nicely in http://sketchucation.com/forums/download/file.php?id=94422

If you want to do it without a plugin, draw 2 lines between the 3 arc points you have, then find the midpoint of the first line and draw a perpendicular from it, then the same for the second line. the intersection gives you the arc centre. Use the circle tool to draw a curve. Erase all the bits you don't need.

But the TIG tools do a better job, and with less fuss.

[jeff hammond]

here's a link to didier's script which tig mentioned earlier..

it includes two methods for drawing arc.. 3pt & center+2pts
http://rhin.crai.archi.fr/rld/plugin_details.php?id=21

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[qiucx]

Thanks all. The TIG tools is good enough for me.

[pilou]

You have the new plugin by Arcs Circles+ by Didier Bur today!