Pie segment (or who likes pie?)

[hwalker]

Below is the picture of the pie in question on the left and the result on the right. It's for positioning reinforcement in circular columns.

Right now on to the hard parts. The radius is 1 and the arc length is 1 as well.

What I want to do is scale it by entering a circumference (easy).

Then I want to enter the arc length and the arc to extend, but still keep the same overall radius / circumference.

[Libbya]

I think you're into the realm of constraints for that.  Post up a file and I'll try to work something up.  

[Libbya]

Actually in rereading your description and thinking about it, I think I could do that with dynamic parameters and actions also.  

[hwalker]

Can't use constraints. I only have LT. Here's the start

[Libbya]

It would be possible using a double lookup and an incremental arc length but would not give infinite adjustment and could be a whole lot of work depending on how high you need the precision to be.  Other than that I'm not sure how to do it without constraints.  I'll think on it a bit.   

[Libbya]

Without using constraints I am not sure how to accurately translate arc length to a rotation angle.  Because of that, the best solution I could come up with is a block that allows you to enter the circumference and then enter the desired arc length.  The block then displays in properties the 'angle to enter' which you need to manually transfer to the 'angle' property.  Once you have done that, the block adjusts to show the correct angle and arc length (or at least as precisely as autocad will calculate).  That extra step is a bit cumbersome but I'm not sure how to do better given the tools at hand.  As I mentioned before, it might be possible to use a double lookup and do the translation between the arc length and rotation parameter but it would lack even more accuracy.  See screencast.  

[hwalker]

Looks good. Arc length needs to be a whole number if that makes using a double lookup easier.

[Libbya]

I meant to attach the block with that last post so you could play with it and I just realized I forgot to save it.  😛  I'll have to work it up again.

If arc length needs to be a whole number that would definitely make a double-lookup version easier.  What are the reasonable limits for the circumference?  Are there reasonable limits for the angle of the arc? 

[hwalker]

Circular columns can vary in circumference, which is why that has to be variable.

Now if you can get it to work on the original 2*pi circumference circle I posted. It should scale up the calculations when the circle is scaled.

[Libbya]

Are there specific specific increments for the circumference or reasonable limits?  The trouble is that I don't know how to transfer the linear distance of the arc length to an infinitely variable circumference.  Without constraints, trying to alter circumference is relegated to altering the angle by using rotation.  In order to use a double lookup you would need increment values for the angle which will result in a bit of error between the actual whole number arc length and the shown arc length unless the circumference just happens to be divisible by pi.  If you are only dealing with circumferences that ARE divisible by pi then it becomes easy.  Even a 1° increment would be a pain to implement, requiring a 360 row lookup table.  

[hwalker]

I'll just have to do it the way I've been doing it then which is breaking a circle of the correct circumference and then lengthening the arc. Thanks for trying anyway.

[Libbya · Accepted solution]

The version I showed before would certainly simplify that process by at least automating the calculation while still requiring a single copy/paste step for adjusting the arc length.  Block is attached.  You can set it to whatever circumference you want and it will scale accordingly.  After the circumference is set, then enter the desired arc length in order to show the correct 'Angle to Enter'.  For the block to adjust to that arc length, you just need to copy 'Angle to Enter' and past it into the 'Angle' property.   On this version copy/paste works fine.  I'll post up the screencast showing how to make and use it after it is done uploading.