Hi,

this no request for help nor a bug report, rather a suggestion and possibly
an invitation to correct my opinion.

A decade ago I used POVray to visualize MRI data. Now I came back to it to
teach my son a demonstrative computer language in the hope that an SDL
which rapidly depicts something you created yourself is far more
fascinating than a typical compiler language where you have way to go until
you see an animate window.

So when reading the current manual I stumbled over a sort of inconsistency
of the SDL. When talking about complex tranformations the manual shows
vectors and matrices and even a matrix product; but here the common rules
of matrix multiplication are twisted. Being used to homogeneous matrices
and vectors in computer graphics - where multiplication means passing
through
rows and columns (respectively) of equal dimension - it looks unfamiliar
(and
at first sight even wrong) that you have to arrange the matrix rows and
columns pivotted around the first diagonal and forget about about equal
size of both.

My suggestion is: allow for the use of 4-dimensional homogeneous vectors and
matrices to be switched on if advantageous. I could imagine that the
calculation overhead could be reduced if successive transformations could
be easily simplified to just one either by the programmer or by POVray.

I have not investigated in the source code about this. But I suppose that
internally POVray is using homogeneous matrices for its computations since
they are so handy; so making them apparent would not be much extra work. If
not, I must concede that the need for this amendment is not big enough to
justify true re-modelling of the source.

So my question is: are there others who'd like to use homogeneous matrices
or am I just too academic?

Be that as it may I find POVray a marvellous program and want to thank and
congratulate the involved programmers.

Yours JWH

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