Could somebody help me and make the situation with <aspect_ratio> element clear? According to the specs (1.4.1):
“The aspect ratio is defined as the ratio of a pixel’s height over the pixel’s width; therefore, the aspect ratio can be derived from, or be used to derive, the field of view parameters: aspect_ratio = yfov / xfov.”
That seems to be incorrect; what we actually need is image aspect ratio.
For example, default camera xfov in 3DS Max is 45 degrees, it corresponds to yfov = 36.6(6) (assuming image aspect ratio being 4:3). Yet default pixel aspect ratio is 1.0. Thus, COLLADAMAX exports camera parameters as follows:
I think you are right, the pixel aspect ratio, and the image aspect ration are two different notion. The first on tells you if the pixel should be square or rectangular, the second tells you if the image is 4:3 or 16:9.
Indeed you can have square pixels in a 4:3 image, or rectangular pixels in the same image aspect ratio. Only one of the parameter is defined in COLLADA, and it mixes both notions.
So I think this was supposed to say “the ratio of the field-of-view’s height in pixels over the width in pixels”, but it got condensed too much.
If that was the intent, then the <aspect_ratio> exported should be 4:3, and therefore this is a bug in the exporter - to be reported to Feeling Software.
So I think this was supposed to say “the ratio of the field-of-view’s height in pixels over the width in pixels”, but it got condensed too much.[/quote]
Furthermore, the ratio should be width to height to obey common usage conventions.
So is this correction clear to everyone?..
“the ratio of the field-of-view’s width in pixels over the height in pixels. An aspect ratio greater then 1 results in a landscape field-of-view.”
“the ratio of the field-of-view’s width in pixels over the height in pixels. An aspect ratio greater then 1 results in a landscape field-of-view.”
I think it is still confusing. Pixel have nothing to do with the intended definition.
Imagine you have a display system with non square pixel. You may very well have a field of view of 4:3 with a 1:1 pixel size ratio.
I would say:
“the ration of the field-of-view is the width over the height of the final image”