Re: [Meshlab-devel] quadric filters

[skunkwerk <sku...@gm...>]

thanks team,
    i did some more testing on the quadric-texture filter with border
preservation enabled, on about 100 different models.

1)  on some models (example file: www.akbars.net/20.zip) you simply can't
reduce the model past a certain number of faces (in this case, 55,000) with
border preservation on - the filter will run, but will stop after having
reduced not all the way... is this intentional?
2)  on some models (example file: www.akbars.net/27.zip) turning on border
preservation results in the model turning into a blob (shape doesn't look at
all the same), whereas with the same number of target faces, the regular
quadric will keep the shape, though lose some faces - is it possible that
the border isn't being preserved correctly with the quadric-texture filter?
3)  is it possible that the lack of the 'preserve normals' option could be
the cause of the different performance between the 2 filters?  would it be
possible to enable this feature for the quadric-texture filter?
4)  is there any way to get an estimation of the "error" introduced by the
reduction, so maybe you could try each filter and go with whichever one has
the least error?
5)  i haven't seen a good explanation for what the "quality threshold"
actually does... how does changing this value affect the reduction?
6)  it seems like the 'border preservation' works best on models that are
not separated into different pieces... is this likely to be true?

all the best,
imran

On Sun, Jul 20, 2008 at 9:52 AM, skunkwerk <sku...@gm...> wrote:

> thanks paolo,
>     i tried it again and the results look much better... though still
> slightly worse performance than the regular quadric.  i'll do some more
> testing.
>
> imran
>
>
> On Wed, Jul 16, 2008 at 11:27 PM, Paolo Cignoni <pao...@is...>
> wrote:
>
>>  Thanks Marco!
>>
>> We did it at the same time. :)
>>
>> Yes it was rather simple.
>> There was a couple a small bugs that i have found when looking in the
>> code,
>> borders were not computed correctly (you used ff topo instead of VF topo)
>> (and i did something wrong when restoring the border preserving markings)
>>
>> So let me commit my version later.
>>
>> p.
>>
>>
>>
>> Marco Pirosu wrote:
>>
>> so i actually implemented it.
>>
>> Then i think i just did copy and paste from the regular one, because i
>> do not remember doing anything special.
>>
>> I don't know why their outcome differs so much.
>>
>> On 7/16/08, skunkwerk <sku...@gm...> <sku...@gm...> wrote:
>>
>>
>>  thanks Marco,
>>        Paolo, is this feature something we could ask Marco to implement?  I
>> re-did my tests, restarting meshlab each time so as not to be affected by
>> the bug you mentioned.  the 'preserve boundary' option does seem to work,
>> but even without it selected the regular quadric preserves much more of the
>> boundary than the quadric-with-texture does.
>>
>> i'm working on fixing the filter texture (texture atlas) plugin right now
>>
>> imran
>>
>> On Wed, Jul 16, 2008 at 1:55 PM, Marco Pirosu <pi...@gm...> <pi...@gm...> wrote:
>>
>>
>>
>>  the original quadric algorithm has been written by paolo cignoni. I
>> think to remember i did not manage it because it wasn't part of the
>> course project, even if the option is there (i think it has been put
>> there in order to be uniform with the normal one). Also, if i remember
>> well. the two algotithms work in a different way. The regular one is
>> dedicated for 3D geometry, while my algorithm is based on the Garland
>> multidimensional algorithm.
>>
>>
>> On 7/16/08, skunkwerk <sku...@gm...> <sku...@gm...> wrote:
>>
>>
>>  it looks like the extra options in the regular quadric filter make no
>> visible difference (i tried reductions with them on and off) -
>> especially
>> the 'preserve boundaries' option that I thought would account for the
>> different performance.
>>
>> but sure enough, the regular-quadric is performing better (dropping less
>> geometry for the same number of output faces) than the quadric-texture
>> filter.  any ideas why?
>>
>> imran
>>
>> On Wed, Jul 16, 2008 at 9:55 AM, skunkwerk <sku...@gm...> <sku...@gm...> wrote:
>>
>>
>>
>>  is that the source of the problem, you think?
>> who wrote the regular quadric filter?
>> would it be possible to copy-paste the code from the regular quadric
>> filter
>> that handles boundary preservation to the quadric-texture one?
>>
>> imran
>>
>>
>> On Wed, Jul 16, 2008 at 4:19 AM, Marco Pirosu <pi...@gm...> <pi...@gm...> wrote:
>>
>>
>>
>>  i think it wasn't part of the course project, so i didn't implement
>> it.
>> It
>> should be doable, through.
>>
>> On 7/16/08, skunkwerk <sku...@gm...> <sku...@gm...> wrote:
>>
>>
>>
>>  there seems to be a difference in the performance of the
>> quadric-with-texture filter and the regular quadric.
>>
>> see these two files:www.akbars.net/classicford.saved.dae (regular quadric)www.akbars.net/classicford.savedtextured.dae (quadric-with-texture)
>>
>> the quadric-with-texture file has polygons missing from the wheels,
>> if
>> you look at them from the side.  is this supposed to happen?  they
>>
>>
>>   were
>>
>>
>>   both
>> reduced to about ~50,000 polygons.
>>
>> Is there a reason the quadric-with-texture filter doesn't have a
>> "preserve boundary" option?
>>
>> thanks,
>> imran
>>
>>
>>
>>
>>
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>> --
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>> Visual Computing Laboratory - ISTI - CNR http://vcg.isti.cnr.it/~cignoni <http://vcg.isti.cnr.it/%7Ecignoni>
>>
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