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Author Topic: localised decimation option would be FANTASTIC ?  (Read 1541 times)

Steve003

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localised decimation option would be FANTASTIC ?
« on: June 24, 2019, 02:28:21 PM »
Hi,
 if one types in 200,000 for mesh decimation, that could be good for an egg cup but bad for a car.
we are saying its got too many faces for what is needed for accuracy, but I have been using a value seen on the internet of 200,000 which I am now thinking is that making my model a bit crude if its 50cm long, and very crude if its a car. If its very ornate is that bad, if its very simple with little detail is that still too much ?
should it not simply be we take 1/10 of the current declared face count and enter that ?

Are we left to decide something that the program would be better at and know best value on given the complexity of the surface ?

If I use 400,000 as I have to see difference on a 38000000 mesh and I am trimming away the base grid I find some pink triangles bite into the model so in fact I need more to avoid that.

advice please on best approach.

Steve
« Last Edit: July 06, 2019, 12:10:37 AM by Steve003 »

Steve003

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Re: should decimation not be by percent rather than a typed in number ?
« Reply #1 on: July 03, 2019, 01:32:53 PM »
Posted 24june, still floundering, hope for some guidance here please, I now have a tyre wall with fine raised number on it formed with a 1mm high raised edge round the numbers.
mesh is 12,566,203 and if I choose decimate, surely that will be 1,256,620    10% of the 12,566,203 but the number appearing in the box when choosing decimate is 300,000 and I have seen offered by default 200,000  I recall trying for 300,000 incase 200,000 was too low. so last value used gets offered again.
Just what number should we be using to retain the 1mm raised beaded edge to tyre wall numbers for example, or the thread on a 12mm diameter bolt on the vintage tyre hub ?
do we have to look at the face count and divide by 10 then use our number ?

I try for 10% and the result is bad. see attached image.

manual says decimate is for pdf and google earth so reading about now decimate mesh in youtube tutorials clearly is wrong for a requirement to get this into a CAD prog to reverse engineer.
However 12.5k will hardly rotate or zoom in photoscan on a dedicated CAD pc.

what percent is advisable to retain detail for export to CAD and surface/curve work such as Rhino3D ?

Also I have chosen high for mesh generation stage after choosing high for dense point cloud, mesh just reached 100% generation and now its decimating it, I dont recall that happening a few projects ago, is that normal ?

Steve
« Last Edit: July 03, 2019, 03:06:09 PM by Steve003 »

Steve003

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Re: should decimation not be by percent rather than a typed in number ?
« Reply #2 on: July 06, 2019, 12:09:48 AM »
Hi,

Further to awaiting advice on decimation, which basically messes up a formerly good mesh for CAD use, all the detail I was enjoying has been nuked, I dont need thousands of mesh on some parts of model (tyre surface) but need detail on screw threads on bolts and details on side wall of tyre, is there a way of reducing mesh on less important areas ?

This would be a FANTASTIC option as why do we have to wreck a model as it contains far to many faces for most of it and makes moving the model around like wading through molasses ?  :(

Steve

Alexey Pasumansky

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Re: localised decimation option would be FANTASTIC ?
« Reply #3 on: July 06, 2019, 12:33:25 AM »
Hello Steve,

The decimation tool is already adaptive and is trying to maintain higher number of polygons to the details compared to the plain surfaces that would be reduced to the low number of polygons.

But I've got your idea regarding the decimation of the selected area only. As a workaround I could suggest to smooth the certain selected areas with high number of steps (strength parameter) and then decimate the model.

The presets settings in the Face Count field of Build Mesh dialog is already a kind of adaptive setting, when the polygon count of the result would be specific for each source data.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Steve003

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Re: localised decimation option would be FANTASTIC ?
« Reply #4 on: July 07, 2019, 12:11:09 AM »
Quote
The decimation tool is already adaptive and is trying to maintain higher number of polygons to the details compared to the plain surfaces that would be reduced to the low number of polygons.
see attached. not v good.
will have to use meshlab or similar to try and reduce mesh yet preserve detail areas.
Quote
But I've got your idea regarding the decimation of the selected area only.
  good, hope to see it soon  :)

Quote
As a workaround I could suggest to smooth the certain selected areas with high number of steps (strength parameter) and then decimate the model.
Where do I find that procedure ? aha smooth mesh dialog box, check box to apply to selected faces, I will explore.

Cheers,
Steve
« Last Edit: July 07, 2019, 12:21:26 AM by Steve003 »