topic Re: Length of Segment of an Arc in Modeling

Length of Segment of an Arc

Anonymous — Mon, 19 Nov 2007 02:01:14 GMT

how does one draw an arc of certain length?

Re: Length of Segment of an Arc

Fran_ois Chatelain — Mon, 19 Nov 2007 08:47:37 GMT

Hi Jae,
here's an object that does exactly that. Either you place it using the radius and sweep angle method and the object will output the length, or you input the length and radius and the object will output the angle. There's also an option to distribute hotspots along the arc. I wrote that thing ages ago so it doesn't have the latest GDL options like line sensitivity, but you can easily trace over it using the hotspots.
Hope this works for you.
Cheers
Francois

Re: Length of Segment of an Arc

Anonymous — Mon, 19 Nov 2007 09:38:13 GMT

thanks a lot. i will try it out and get back

Re: Length of Segment of an Arc

__archiben — Mon, 19 Nov 2007 21:35:05 GMT

another way is to use your special snaps . . .

it involves placing the line longer than you need first - next set up your special snaps to show increments by 'distance' and enter the value of the distance you need.

hover your mouse over the end of the arc that you want to measure from and the snaps points will appear. grab the other end of the line and stretch back to it. be quick!

there may be an easier 'on-the-fly' method, but i didn't investigate too thoroughly . . . (link will set me straight if there is! )

~/archiben

Re: Length of Segment of an Arc

Link — Mon, 19 Nov 2007 22:06:21 GMT

~/archiben wrote:
there may be an easier 'on-the-fly' method, but i didn't investigate too thoroughly . . . (link will set me straight if there is! )

There is with straight lines, using the special snap constraints, but not with arcs AFAIK.

You could also force a guideline (` key) using your method if you didn't want to rush, but you'll need to be conscientious about where you placed your cursor to show the special snap points. Hover close to the originating end of the arc.

Cheers,
Link.

Re: Length of Segment of an Arc

Anonymous — Tue, 20 Nov 2007 02:36:17 GMT

hello francois
Iam not able to open the arc.gsm file.

thanks to all of you for the help

Re: Length of Segment of an Arc

Fran_ois Chatelain — Tue, 20 Nov 2007 08:05:39 GMT

Hi Jae,
the file is an object, so you have to put it in your active library(ies) and reload them. Then you should be able to access it through the object tool.
Let me know if this works. I've attached another copy, should the other one be corrupted.
Cheers
Francois

Re: Length of Segment of an Arc

Fran_ois Chatelain — Tue, 20 Nov 2007 08:07:59 GMT

And I forgot to mention that the object is to be used as a "template" allowing you to trace over it using its hotspots.
Cheers
Francois

Re: Length of Segment of an Arc

Rex Maximilian — Thu, 22 Nov 2007 09:55:53 GMT

~/archiben wrote:
another way is to use your special snaps . . .

it involves placing the line longer than you need first - next set up your special snaps to show increments by 'distance' and enter the value of the distance you need.

hover your mouse over the end of the arc that you want to measure from and the snaps points will appear. grab the other end of the line and stretch back to it. be quick!

there may be an easier 'on-the-fly' method, but i didn't investigate too thoroughly . . . (link will set me straight if there is! )

~/archiben

Geniusly simple solution...

You could also place a hotspot, and then stretch back the arc at a relaxed pace.

Re: Length of Segment of an Arc

Rex Maximilian — Thu, 22 Nov 2007 10:21:55 GMT

Math is our friend:

If the circumference of a circle is:

C = pi 2r

The we can assume that a partial circumference, (the distance you wish to draw the arc of the circle) is the following formula:

C = (pi 2r) x (sweep/360)

So, we need to solve for the sweep angle since you will know what radius and distance of the arc you want to draw.

C/sweep = (pi 2r)/360
1/sweep = ((pi 2r)/360)/C

Results in the following formula:

sweep = C/((pi 2r)/360)

Plug in the values you know. Let's say you want a 30m long arc with a 5m radius:

sweep = 30/((pi 2x5)/360)

and use your trusty calculator:

sweep=343.77°

So use the arc tool by drawing out from the center 5m and entering an angle of 343.77°. That will give you your desired arc length of 30m.

Re: Length of Segment of an Arc

Fran_ois Chatelain — Thu, 22 Nov 2007 10:28:21 GMT

Hi Rex,
which is exactly what my object does
Cheers
Francois