Re: Question: Determine Size of polygon

New Message Reply Date view Thread view Subject view Author view

Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Wed, 23 Aug 1995 13:11:18 -0600

On Aug 23, 6:15pm, Terence Ker wrote:
> Subject: Question: Determine Size of polygon
>
> I want to add a building in my Performer scene using simple polygons
> with transparent textures on it, exactly like most of the trees were built
> except not using the pfBillBoard node. I took the picture I want, scan the
> picture to get the image file on my computer, make those non-building portion
> transparent ( alpha = 0.0f ), and now comes the question, how big should
> I make the polygon to let the texture look good on it. What is the proper
> size of the polygon?
>
>-- End of excerpt from Terence Ker

I'm not sure I follow you, this polygon is in 3D so you should make it the
size of your building and in the correct place. The coordinate system you use
is arbitrary so pick a scale, an arbitrary rendering unit of 1m is fairly
typical but you could use banannas per furlong and it would still work.
If youre inserting the polygon into an existing database you could read the
position information displayed in the perfly GUI to get an idea of
where and how big your building should be.

To ensure decent quality with varying polygon sizes use a BILINEAR texture
magnigication filter and a MIPMAP_TRILINEAR texture minification filter. This
will make the texture VS polygon size less of an issue for you.

If youre making the building an arbitrarily long way away and want it to have
an appropriate size then use ratios. If you know the angle you want it to
subtend then tan (theta/2) = (half poly size) / distance, where theta is
the angle you require and the polygon is oriented towards where you expect
the eye to be.

I hope the answer you want is here somewhere.

-- 
Angus Dorbie,
Silicon Graphics Ltd, UK
dorbie++at++reading.sgi.com

New Message Reply Date view Thread view Subject view Author view

This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:51:49 PDT

This message has been cleansed for anti-spam protection. Replace '++at++' in any mail addresses with the '@' symbol.