Well, I *usually* use a unit system based on Ft=1 unit, but there are times
when I don't want that for some reason.  I think having the units in an
include is easier to work with since if I want a different scaling all I
have to do is change 1 variable and everything else is now changed, without
breaking compatibility between scenes.  something that is 4 Ft in one scene
will still be 4 Ft in another scene, regardless of what Ft is set to.  There
was some discussion of this recently
(http://news.povray.org/povray.general/32603/?ttop=32932&toff=50) and from
the feedback in that thread I gather that many POVers are using a similar
system.

As far as making objects portable, all I have to do is put the neccesary
unit definitions for that object in the include file, and if you want to use
it in your scene, set Ft to whatever works.  I think having it coded into
the parser would be less flexible.

And I suspect that there's no way around having to rescale some things,
simply because certain objects (i.e. height_fields, superellipsoids, etc...)
have a fixed size upon creation.  That's one of the primary reasons I don't
*always* use the same unit scaling.  If I'm building something from prisms &
lathes, using splines I created in a separate spline editor, then I'm going
to use whatever is easiest to work with those splines and the odds are that
it isn't Ft or Cm.  Also, meshes imported from other modelling software are
not standardised in their scaling, so depending on the ratio of imported
meshes to native POV objects, I may or may not use my standard units.

I'd say the only way such a system would really be practical is if not just
POV, but every modeler, editor, etc out there was standardised to it.   Good
luck!

And what is unit-less? Whether you give it a name or a number, POV expects
units, so why not keep it simple and let each artist work with whatever unit
they're comfortable with? And like I said above, if you want to share your
objects, just put the relevant definitions in your include. Then whoever
wants to use it can set 1 unit to whatever they like... change one variable
and everything works fine.

RG


Alan Smith <ala### [at] aurora-ukcom> wrote in message
news:3f4b68aa$1@news.povray.org...
> Am I correct that POV-Ray does not support units of measurement
> ie (mm, cm, m, km, in, ft etc)?
>
> Wouldn't it be nice if POV allowed something like :-
> box { <-2cm, -1cm, 10mm>,  <2cm, 1cm, 1cm> }
>
> This would lead to more readable code, greater ease of 'real world' scene
> modelling with mixed sizes of objects and, most importantly, greater scope
> for sharing objects from other people who generously donate their source.
>
> At the moment I achieve this by using suitable declares and coding as :-
> box { <-2*cm, -1*cm, 10*mm>,  <2*cm, 1*cm, 1*cm> }
>
>
> Which goes a long way to meeting my needs, but it still does not do
anything
> for supporting portability of coded objects between scene files.
>
> This would surely be a simple modification to the parser and would still
> leave the ability for people to work in a 'unit-less' fashion if they
like?
>
> Alan Smith.

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