Triangle angle sum > 180!

Attention! This seems to be a bug prior to 2.46!
I was running version 2.45 under Mac OS X 10.4.x, but I tried both version 2.45 and 2.46 under Windows XP , and the bug is only present in the 2.45 version.

Well the title says it all, I’m simply not understanding why blender is telling me that an equilateral triangle has two angles of 60 and one of 71,490, giving me an angle sum of 191.490 :confused:… If I, in the transform properties palette, set the values to local, it works perfectly giving me three angles of 60 and a sum of 180, but if I use global values then one of the angles is screwed up. I just want to know how this is even possible and why blender does like this…

Here is an image and the source blender file to let you see what I mean: Equilateral Triangle

Thx.

I believe if the points aren’t all in the same plane, then this could happen.

I think this happens because blender will use dot products to calculate the angles and so if they aren’t in the same plane you’ll get a “3d-angle” so to speak (it will calculate the angle between two 3D vectors instead of two 2D vectors).

don’t think so - that’s called a triangle and it always form a plane in 3D!
if this was 4 verteces then may be if theiy are not all equiplanar then this wold be kind of a problem!

in any case can you show a pic of that thing!
Saluations

Can you upload a file ?
Or describe the exact steps to take to reproduce it ?

A triangle is alwats only in one plane.

AND WILL BE able to analyse it

another thing is that if you want to make a triangle you can add a circle with 3 segments

then change the location of the verteces
i tried a test to show the angles and to no vail i cannot see the agnles
i can see the lenght of edges but not the angle?

Thanks

is the other angle 120 or 109?

BTW I hope you know which one I mean.
also what is it?

I can’t duplicate this behavior. I added a three vertex circle (equilateral triangle.) The angles were all 60 degrees. No matter how I rotated the triangle, the angles remained 60 degrees, in both local and global. I added more geometry, but the angles remained 60 degrees.

You may have found a bug. There is no way Blender should be reporting anything other than 60 degrees for all three angles. Do you recall what exact steps you used to make that model? Can you reproduce it from scratch? If so, forward the blend to the bug tracker.

If you play with it enough, you can eventually get an apparently equilateral triangle where the angles aren’t sixty (they still sum to 180, though). This shouldn’t change between local and global either, since either way the relationships stay the same. This could be expected in some minor ways, since computers are not precise with floating point, but I don’t think it should have an extra ~11 degrees.

To all the people screaming about how a triangle can only be planar no matter its orientation, yes I realize this (cough didn’t think about what I was writing :rolleyes: cough), but as I said above you can finagle the floating point accuracy beyond where the interface will show it. Python, however, will show it (that it’s not truly equilateral), but the interface won’t. Still, it shouldn’t be 11 degrees of difference and they would still sum to 180.

I would guess this may just be a fluke in your blend file (especially since nobody else can reproduce it) but as said above posting it will help diagnose it. Try appending the mesh to another file to see if the problem persists.

there is an excecption to this -
if you have 3 verteces on a sphere --> angles > 160 degrees
but i don’t think blender can calculate that situation i mean on a spherical coordinates system
blender use the ordinary rectangular coordinates sytem
interesting subject ayway

Salutations

Many replies, I thank you for that :slight_smile:

I actually sat trying to visualize a triangle in 3D thinking if it could have something to do with the plane of the triangle, but just as several of you stated, that is impossible as tris are single planed.

RickyBlender: “to make a triangle you can add a circle with 3 segments” making a note :eyebrowlift2:. And go to Edit Panel (F9) -> Mesh Tools 1 -> Edge Angles, to turn on showing angles (only if verts creates a face that is).

I got the file uploaded too, you can find it at the link in my first post.

This is how I did it:

  1. [alt-x]: Erase all
  2. [kp_1]: Front view
  3. [x]: Erase cube (if any)
  4. Add -> Plane
  5. Merge the 2 lower verts at center
  6. And there you go

I’ll send it to the bug tracker tomorrow.

P.S. Yay! I found a bug! :smiley:

I don’t see any bugs in the file you uploaded (angles add to 180, no difference between global and local).

Can’t recreate it using the steps you posted either. Does it happen in every file (i.e. if you retry the steps in a blank file does it happen?)?

Are you using 2.46? What system/OS?

Attached a pic of your file as I see it.

Attachments


but whne i tried with the circle i was not able to get the angle
why is unknown !
i can get it with a plane but no with 3 segment circle - it’s bizar that;s all

Saluations

Attention! This seems to be a bug prior to version 2.46!
I was running version 2.45 under Mac OS X 10.4.x, but I tried both version 2.45 and 2.46 under Windows XP , and the bug is only present in the 2.45 version.

You wil have to fill the face, either at the add dialog by pressing the fill button, or do it afterwards.

fiill faces seems to be working fine to get the angles indicated

mind you the length are there face or not!

Thanks

The only way to get interior angles of a triangle to != 180 is to project the triangle onto a sphere or other non-flat surface, and then measure the normal of those angles

If you Remove Doubles and it merges a total of more than 1x10^33 vertices, a virtual singularity may form in your .blend, causing a local disturbance of Blenderspace that can cause all sorts of geometric weirdness like interior angles > 180 deg. :eek:

Try it sometime! :eyebrowlift:

are you saying that we can measure angles of triangle on a sphere

Salutations

How are you supposed to project a triangle onto a non-flat surface?

A singularity forming in my blend file would be the least of my problems: My comp would blow up before getting close to 10^33 verts :stuck_out_tongue:

you can laydown on a sphere a triangle with retopo

Salutations