I use PovRay at work to do 3D views of new window products. It is a real pain to
first create the shape in AutoCAD, extrude it, save it as 3DS, convert to mesh2,
then render. Is there some way we could have a prism type that would allow
curves instead of straight lines?. I know all about the other line types, but
frankly they are cumbersome. Ideally I would like to reads in the DXF polyline
and then use it in a prism.

The rendering I have done have been impressive to the architects and owners and
they all ask if I used AutoCAD...no, I say, I use POVRay!

Jay

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"JayWiz" <nomail@nomail> wrote:
> Is there some way we could have a prism type that would allow
> curves instead of straight lines?. I know all about the other line types, but
> frankly they are cumbersome. Ideally I would like to reads in the DXF
> polyline and then use it in a prism.

I have no idea about the DXF polyline, but doesn't any of the linear_spline /
quadratic_spline / cubic_spline / bezier_spline prism types do the job?

Then again, it seems that your problem is not so much how to represent it in
POV-Ray scene language, but the workflow of getting it from DXF to there
without going via braindead triangle meshes, right?


Maybe it's time for a project aimed at getting different file formats converted
to POV SDL without reducing POV to a mere mesh renderer (after all, it *can* do
spline-based prisms, it *can* do bezier patches, it *can* do... well, quite a
lot.

.... or maybe even "include" them directly from SDL somehow?


> The rendering I have done have been impressive to the architects and owners
> and they all ask if I used AutoCAD...no, I say, I use POVRay!

Heh, great to hear - looks like it is *some* good after all ;)

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> Maybe it's time for a project aimed at getting different file formats 
> converted
> to POV SDL without reducing POV to a mere mesh renderer (after all, it 
> *can* do
> spline-based prisms, it *can* do bezier patches, it *can* do... well, 
> quite a
> lot.

I would love a converter from STEP files to POV SDL.  STEP files are a 
standard format for interchange of 3D CAD data, and are made up of bounded 
planes, spheres, torii and bezier patches etc.  I don't know of any software 
that can render these files without tesselating to a triangle mesh first.

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"clipka" <nomail@nomail> wrote:
> "JayWiz" <nomail@nomail> wrote:
> > Is there some way we could have a prism type that would allow
> > curves instead of straight lines?. I know all about the other line types, but
> > frankly they are cumbersome. Ideally I would like to reads in the DXF
> > polyline and then use it in a prism.
>
> I have no idea about the DXF polyline, but doesn't any of the linear_spline /
> quadratic_spline / cubic_spline / bezier_spline prism types do the job?
>
> Then again, it seems that your problem is not so much how to represent it in
> POV-Ray scene language, but the workflow of getting it from DXF to there
> without going via braindead triangle meshes, right?
>
>
> Maybe it's time for a project aimed at getting different file formats converted
> to POV SDL without reducing POV to a mere mesh renderer (after all, it *can* do
> spline-based prisms, it *can* do bezier patches, it *can* do... well, quite a
> lot.
>
> .... or maybe even "include" them directly from SDL somehow?
>
>
> > The rendering I have done have been impressive to the architects and owners
> > and they all ask if I used AutoCAD...no, I say, I use POVRay!
>
> Heh, great to hear - looks like it is *some* good after all ;)

The normal lathe uses straight lines to connect the "dots". If a curve could be
used then the polyline object from autocad (or TurboCAD which I also use) could
be easily translated. The other lathe types are not really condusive to the
objects I use. I have attached a sample image of what I show to customers and
P&D for their use.

Jay

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Attachments:
Download '90ssgmull.bmp' (577 KB)

"JayWiz" <nomail@nomail> wrote:
> The normal lathe uses straight lines to connect the "dots". If a curve could be
> used then the polyline object from autocad (or TurboCAD which I also use) could
> be easily translated. The other lathe types are not really condusive to the
> objects I use.

"Curve" is a bit vague, as all the quadratic_spline, cubic_spline and
bezier_spline would fall into that category.

I just googled for what type of spline AutoCAD's "polyline" actually is,
mathematically, only to find that it's not a classic spline at all...

From a geometric point of view, a polyline lathe should be representable as an
(albeit possibly non-trivial) CSG object composed entirely of linear_spline
lathes and tori, and a polyline prism as a CSG object composed entirely of
standard linear_spline prisms and cylinders.


So that might be a point for the To-Do list: Implement a new spline type,
defining a path made up of straight lines and circular arcs.

Question to you as someone familiar with AutoCAD: How's a polyline actually
defined in AutoCAD? Is it basically a polygon, with corners rounded using a
standard radius? Is it a polygon with corners rounded using different radius
for each corner? Or a free intermix of straight lines and arcs?

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"clipka" <nomail@nomail> wrote:
> "JayWiz" <nomail@nomail> wrote:
> > The normal lathe uses straight lines to connect the "dots". If a curve could be
> > used then the polyline object from autocad (or TurboCAD which I also use) could
> > be easily translated. The other lathe types are not really condusive to the
> > objects I use.
>
> "Curve" is a bit vague, as all the quadratic_spline, cubic_spline and
> bezier_spline would fall into that category.
>
> I just googled for what type of spline AutoCAD's "polyline" actually is,
> mathematically, only to find that it's not a classic spline at all...
>
> From a geometric point of view, a polyline lathe should be representable as an
> (albeit possibly non-trivial) CSG object composed entirely of linear_spline
> lathes and tori, and a polyline prism as a CSG object composed entirely of
> standard linear_spline prisms and cylinders.
>
>
> So that might be a point for the To-Do list: Implement a new spline type,
> defining a path made up of straight lines and circular arcs.
>
> Question to you as someone familiar with AutoCAD: How's a polyline actually
> defined in AutoCAD? Is it basically a polygon, with corners rounded using a
> standard radius? Is it a polygon with corners rounded using different radius
> for each corner? Or a free intermix of straight lines and arcs?

A polyline is defined using both straight lines and arcs.

AutoCAD uses radial as a default. The user can then redefine the curve by moving
the endpoints, start angle, end angle, and radius. It also has a center point
and a direction. With this information AutoCAD makes a corner. The corner can
be stretched (made eliptical).Perhaps for a general description, the curve
could be an elliptical curve with a circular curve as a special case. AutoCAD
stores the curve as a true curve but when it is extruded it uses a user defined
number of straight faces with smoothing normals to appear curved, which is why
AutoCAD renderings seem of low quality.

I will post a binary view of a sample rendering (with a low resolution) in the
binary newsgroup.

Jay

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in news:web.4988364b805a7c7eea031d410@news.povray.org clipka wrote:

> So that might be a point for the To-Do list: Implement a new spline
> type, defining a path made up of straight lines and circular arcs.
> 
> 

Iirc Ron Parker implemented a 'torus-spline' like that as a macro using 
sections of cylinders and torus objects.

ingo

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