[WS2122] Homework 2 Discussion

[changkun]

This thread is open for the discussion of homework 2.

[nico778]

Hi, I tried to use my halfedge-structure from the first homework, but nothing is displayed after importing a mesh. I'm guessing my halfedge-structure must be wrong then, or do we have to change something else?

[changkun]

Sorry for the late response. I think we are not that strict here. So the results are evaluated on the rendering result, if you could produce visually comparable results, then they are the same.

From the second exercise, the change might be from an open boundary mesh to a watertight mesh (although I have not yet evaluated all submissions yet)

[Consti10]

Hello,
Quick question regarding the "fork and branch workflow" should the pull request for the solution of the second homework also
contain the previous homework solution or not ? I'd think the files on the second pull request should look like this,right ?

Option 1(yes):
homeworks/constantin/2-ddg
And not like this:
homeworks/constantin/1-halfedge
homeworks/constantin/2-ddg

[changkun]

The new PR should not contain previous commits. Hence, yes, option 1 is preferred.

[Consti10]

Are we allowed to extend the geometric math functions of the project ?
For examle a helper to construct a Vector from 2 Vertices.
return new Vector(pos2.x-pos1.x,pos2.y-pos1.y,pos2.z-pos1.z);
aka I'd like to not write the above code every time ;)

[Consti10]

Found the proper helper(s) in "vec.ts".

[JohannesMerkt]

Hi,
im stuck. So far all i have done was to take the halfedge code from the first homework and copied it over while making sure it works in the first assignment, but i cant see anything at the moment. What do i have to do to see my geometry? Before i start working on the normal and curvature implementations

[JohannesMerkt]

Got it so if you just want to see the geometry try setting the normal vector to 1,1,1,1 and the curvature to 1 too

[Consti10]

Yes, then you should get an image.

[changkun]

Yes, that's great sharing. I think we briefly talked about this in precense, did we?

[Consti10]

yes, but we only found out that you have to set both normal and curvature to default values late after the lecture :)

[JohannesMerkt]

Hi,
I am confused. The halfedge implementation has a function called angle with a todo message: compute the tip angle at this edge. So does that mean I should calculate the angle of the corner of the triangle or should I calculate the redefined angle which is considering the geometry is smooth?

I assume just calculating the triangle angle makes the most sense here

[Consti10]

I think the angle() method is intended to be used when calculating the Normals in "AngleWeighted" mode. Therefore I'd calculate the "corner Angle" aka Theta1,2,... .

[Consti10]

Actually, I think I only now understand your question correctly - basically you are asking if in angle() we should scale the angle such that the sum of angles is 2Pi again ? No idea ;)

[JohannesMerkt]

Now that i finished it. Im quite sure its without having the sum of the angles sum up to 2Pi

[changkun]

Actually angle is the angle of the opposite side of an halfedge.

[changkun]

Or can be interpreted as the adjacency angle of an halfedge (depends on the implementation)

[alvaxgln]

Hey i'm having a lot of problems...

My halfedge implementation worked fine for homework one, so first i copied over halfedge.ts, but that gave me an error cause it couldn't find "linalg.mat" and "linalg/quaternion" (are those needed? Should i copy those over too?)
So i just replaced the buildMesh() function with my implementation from homework one, and set the normal and curvature to 1.
But when i start the program it just gives me a black screen, with the controls, and none of the controls are clickable.

Not sure what the problem is here

[Consti10]

The default mesh now has much more vertices than the previous one. In my case, the halfedge building code was not using a hash map an therefore took ~20seconds to build. So I thought at first the controlls were not working.

[changkun]

couldn't find "linalg.mat" and "linalg/quaternion"

These are actually re-located. So you may have to change the code a little bit rather than a direct use. The purpose is to let you rethink the whole situation and do some adaption.

I also uploaded a reference solution, which you may use directly to get faster load speed.

[alvaxgln]

Ah, ok thank you

[JohannesMerkt]

If nothing is happening and your browser tab freezes its likely that your code isnt ver optimized. With my code from the first homework it took minutes to load the mesh 😂

[Consti10]

When calculating the "Gaussian Curvature" aka CurvatureMethod.Gaussian can we just use the angle defect ?

[changkun]

Yes :)

[Consti10]

Should you be able to observe a difference on the normals when changing the "normalMethod" ?
In my case, all 3 of them give exactly the same results, at least when looking at the rendered Image. Haven't checked the raw vec values yet.

[JohannesMerkt]

At first glance I thought they where the same but on close inspection you can see some minor changes. Btw you can zoom an pan on the 3d model

[changkun]

You should be able to observe changes between different normal methods, if you activate showing normals.

Note that you must be very close to the mesh to see the differences.

[Consti10]

okay, I will look more closely on the rendered image. Looking at the raw vec values, they are slightly different.

[Consti10]

Thanks, now I can see it too. Most noticable at the ears ;)

[alvaxgln]

I'm currently trying to calculate the area of the voronoi cell around a vertex.
Is there a more convenient way to do that, than finding the circumcenter of each face?

[nico778]

if I'm not mistaken it can be done with the cotangents of the halfedges

[changkun]

Close due to the end of the submission period.