Add_arc etc.

Wo3Dan

@wo3dan said:

b.t.w. Why would the API mention (as a learning example for add_arc) two "wako"angles in radians, to have a 1145 degrees arc as a result?

Because the API docs like to keep you on your toes. The author probably intended them to be degrees. (Would have been a nice example of the .degrees method: 45.degrees)

Word of advice: don't trust the API docs to be correct. Least not provide best practice examples. (For instance, it notoriously use .typename to compare entity types - which is horribly slow. Instead .is_a() should be used. So many plugins run slow because of this.)

Thanks Thomas, for the warning. I'll keep that in mind.
As for the advise.....printed and saved for use later.
I'll take things step by step, making usefull examples (at last for me), more or less according TIG's advise about the one_liners. Besides that I try snippets and alter them. And read and try to memorize the huge amount of info.
Step by step I hope to get there in the end.
Thanks again.

thomthom

Yea, that's how I got started.
Small little tasks that piece by piece let me wrap my head around how it all worked.

honkinberry

I'm having a devil of a time with add_arc, and this seemed the best place to ask.

I have, for instance,


entities.add_arc ORIGIN, X_AXIS, Z_AXIS, 100, 4.6998, 1.6823

Which should make an arc roughly resembling the curve of an upper-case D.
But instead it's making a C.
Start angle is 4.6998, end angle is 1.6823....
So, what am I missing???

--J

thomthom

4.6998 and 1.6823 radians is 269.278704555584 and 96.3886898748584 degrees which gives you an arc of 172.890014680726. That sounds like a C shape to me.

Where do you get your numbers from?

This, will be D-like:
entities.add_arc ORIGIN, X_AXIS, Z_AXIS, 100, 5.degrees, 175.degrees

This will be a true half-circle:
entities.add_arc ORIGIN, X_AXIS, Z_AXIS, 100, 0, 180.degrees

honkinberry

Those are the values from the Arc in AutoCAD.
If the Start is roughly 270 degrees, and the End is roughly 90 degrees, that is a D shape, not a C shape.
Angles accrue in counter-clockwise fashion, yes? So from Start angle, one begins slowly spinning in a counter-clockwise fashion until reaching the End angle.

--J

thomthom

Yea, it seems to be counter-clockwise - and then the C-shape makes sense. If you use the Protractor and uses the same angles to add guides, then adding then counter-clockwise from the X-axis places them exactly where add_arc draws the arc.

honkinberry

I'm sorry, I'm just not following.
I'm Susan, I'm standing at the origin, and I'm pointing at at object down the negative Green axis, at 270 degrees relative to me. It is a car, and it is driving in counter-clockwise circle around me. As it drives counter-clockwise towards a point located at my 90 degrees, the resultant path it drew was a D shape, not a C shape.

I've dealt with arcs extensively with AutoCAD, and as I said, this is just taking the exact arc in AutoCAD and recreating here in SketchUp. But some of my arcs are getting reversed, and I can't figure out what I'm supposed to be accounting for.

--J

thomthom

Right, I see.

Maybe SketchUp normalize the start and end angle - because swapping the values around creates the same arc. ??

You might have to use negative angles.

honkinberry

Ah, I'm starting to get it.
I made the same mistake when I was a 19 year-old programmer.
If the arc crosses 0 degrees, it will get reversed.
So you're right, Sketchup is sort of normalizing the arc. Or put more accurately, it's a bug -- it assumes the start angle to be less than the end angle.
So easy enough fix -- if (start > end) start = start - 360.degrees
Thank you sir!

--J

thomthom

Probably be good to make a wrapper for the add_arc method.