should glTF specify unit property ?

[fabrobinet]

No description provided.

[RemiArnaud]

probably not, but converter needs to.

converter parameter: unit size in meter
then converter use the unit definition in the dae, and then apply the
scaling.

[fabrobinet]

Sounds good to me.

[pjcozzi]

@RemiArnaud does unit size in meters need to be a dae2json option? It is already part of COLLADA with the unit element of the asset element.

[RemiArnaud]

the converter needs to know what unit to convert to, so yes, it is a
parameter to the converter.

the application need to deal with whatever it gets if it does not have
access to a converter? if yes, then specify the unit in the glTF as well.

[tparisi]

There are only two choices: put a units metadata field in the format, or mandate glTF units (presumably at meters).

I'm ok with either, but I have a pretty strong preference for doing it the COLLADA way. That way artists and programmers can work in whatever they feel comfortable with and the engines/readers don't really care. They just have to convert from the specified units to their native runtime units. This doesn't seem to be broken in COLLADA, why fix it?

[RemiArnaud]

I have been thinking about this one for quite some time.

I say - let's use 1 meter as the glTF unit.

We already say we are Y_UP, so it is aligned previous decisions. Surely make it simple to mash-up models from various part of the web - exact same coordinate system.

I have reviewed a bunch of use cases in my head, so ready for arguments now :-)

[pjcozzi]

Any updates here?

I thought I originally included the unit element in asset from COLLADA, but I did not. I must have decided against it. Given that, I am OK with @RemiArnaud's proposal to define the units in meters, but don't have too strong of an opinion.

[pjcozzi]

Any update?

[fabrobinet]

I am fine with meters too...

[pjcozzi]

Adding converter label since this will require converter support.

[pjcozzi]

@fabrobinet any update on converter progress for this. There is some interest.

[fabrobinet]

@pjcozzi what exactly needs to be done ? dev-4 is fully packed and I could use some help on this one :)

[pjcozzi]

This would just rescale positions so that the units are meters if the input COLLADA units are not meters.

[meshula]

I'm all for meters with the conversion @pjcozzi mentions. I've spent way too much time maintaining converters where units can change per file, and trying to work out what was intended when files with different units reference each other. Knowing that 1 == 1 no matter what sounds like heaven.

[fabrobinet]

ok with me, we'll have to be careful of animations and make sure their translations are rescaled too...

[tparisi]

I'm ok with this - as long as we understand that it puts all the onus on
the converter.

Tony

On Mon, Jan 20, 2014 at 8:14 PM, Fabrice Robinet
notifications@github.comwrote:

ok with me, we'll have to be careful of animations and make sure their
translations are rescaled too...

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[fabrobinet]

Indeed, that's always the choice we make. More work on the converter, less work to import models for viewers&engines...

[pjcozzi]

All sounds good. Good point about the animations.

[RemiArnaud]

+1

-- Remi

On Tue, Jan 21, 2014 at 9:41 AM, Patrick Cozzi notifications@github.comwrote:

All sounds good. Good point about the animations.

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[yashafromrussia]

Hey, any update on this?

[fabrobinet]

added for dev-7. Maybe @pjcozzi should you could look at with @tfili ? I guess it's important for cesium..

[fabrobinet]

Keeping for spec

[pjcozzi]

@tparisi for the draft 1.0 spec, add:

Units are in meters.