[Uni-verse] Minutes from todays PCC meeting

[Lauri Savioja]

Dear Gert,

Thanks for the minutes. I have one minor comment and one question:

1) HUT was represented in the meeting as well :-).

2) Could you, please, be more specific on the requirements related to
acoustic materials and reduction module. Both of these parts were
expanded since previous round and I don't what we should add to the
description. If you wish to have the error metrics for the reduction,
please find the description as decided in discussions with FIGD in the
following:

--- start of the error metrics ---

We have two reduction schemes. The first and the simpler one:

Only vertices, which are connected to polygons with the same acoustic
material can be reduced. Error function (per vertex) is as in [1] for
the vertices. The reduction is performed as in [1].

The second and perhaps finer scheme is as follows:

The per-vertex error function: E(v)=Gerr(v)+Merr(v), where
 - Gerr(v) is geometric error for vertex. This is the error as in [1]
 - Merr(v) is material error. If polygons connected to v are of same
   material, Merr(v) is 0. Otherwise Merr(v) is nonzero and function of
   the surface areas and materials of connected polygons. More exactly,
   something like:

     P1,..,Pn are the polygons connected to v.
     M(Pi) is the material vector of scalars for Pi
     A(Pi) is the surface area of Pi

           (A(P1)*M(P1) + ... + A(Pn)*M(Pn))
     Mavg= ---------------------------------
                  A(P1) + ... + A(Pn)

     Merr= A(P1)*||M(P1) - Mavg|| + ... + A(Pn)*||M(Pn) - Mavg||

     In other words, Mavg is surface area weighted material average.
     Merr would be something like material variance in
     surrounding polygons. However, We don't know how the material
     vector norm || · || should be defined in this context. The
     usual vector norm (|| · ||_2) perhaps?

After vertex removal, materials of affected polygons must be adjusted. I
think Mavg is suitable material vector for all affected polygons, as it
was the weighted material average of surrounding polygons.

However, this scheme has still the open issue of definition of
|| · ||. Additionally, the error functions Merr and Gerr need to be                
scaled appropriately. The scaling factors must be experimented.

We will start with the scheme 1. If this proves to be
insufficient, then we shall go for scheme 2. But the path to
the scheme 2 should be kept open.

References:
[1] Sahm, Soetebier, Birthelmer. Efficient representation and streaming
of 3D scenes. Use keyword: sahm soetebier at URL: 
http://www.elseviercomputerscience.com.

--- end of the error metrics ---

Regards,
	Lauri

On Mon, 24 May 2004, Gert Svensson wrote:

> This is the minutes from todays PCC meeting.
> 
> Note: next meeting at 14th of June at 13.00 CET DST
> 
> Best Regards
> Gert



-- 
Lauri Savioja
Telecommunications Software and Multimedia Laboratory
Helsinki University of Technology
PO Box 5400, FIN-02015 HUT, Finland
Tel. +358-9-451 3237     Fax +358-9-451 5014