Request for help

Request for help

Post by Joshua Gord » Sat, 15 Sep 1990 10:50:46

Hello! I'm developing a program that (among other things) will
be implementing the algorithm on page 108 of "Science of Fractal
Images" by Peitgen and Saupe. It's working fine; but I've come
across something I don't understand. On pages 106 and 107 are
a sequence of spectrally synthesized mountains. On page 109:

"In the sequence...we show how the spectral synthesis method
'adds detail' by improving the spectral representation of the
random fractal, i.e. by allowing more and more Fourier coefficients
to be employed. The resolution...was N=64 but in the top image...
only the first 4 coefficients were used. In the other pictures we
allowed 16 and 64 non-zero coefficients..."

Now, here's my problem. I'm not sure _where_ to pick the "first
M coefficients.", and how to pass that information to the Fourier
transform. Obviously, some of the coefficients need to be zeroed
out, but which ones? The key to making it work right is satisfying
the conjugate symmetry condition mentioned on page 109, but I'm
still at a loss figuring out which are the "first" ones. It is not
just the first M ones calculated; the algorithm as presented does
a fairly optimal job of calculating the things. (Though there are
some redundant calculations.)

Could anyone help me with this? Fast? Help?

Respond by mail (if it is interesting enough, I suppose you could
post it here too!) to either the reply-to up above, or to



Request for help

Post by Ben Fe » Tue, 18 Sep 1990 01:18:51

I need a program to convert an Amiga HAM to either a .GIF or an IFF file.
Does such a program exist for MS-DOS?


I asked YOU who's at DDSW1! Ok, there's a guy at DDSW1, right? | Right!
Who? | Exactly! | What? | No, he's at lll-winken. | Where? | No, What! |  I
don't know! | He's at gargoyle. | Who? | No, he's at DDSW1.MCS.COM!


1. Request for help regarding collision detection

Say I have a scenario in which a game is using a BSP tree as a secondary
data structure for a triangle mesh environment, and the environment is
basically a series of connected rooms with stationary objects (which can
be hidden behind) and movable objects. The movable objects can be
thrown by both computer avatars and a single human avatar.

Using AABBs for character-character and character-environment
collision detection and AABBs for throwable object collision detection,
is it possible to use only the AABBs for collision detection without
using a narrow phase, exact triangle-triangle intersection for the moving
objects? i.e. would this be sufficient for my proposed game?

The reason I ask is that
I understand that a problem arises when the bounding boxes intersect
without the actual objects coming into contact.

However, I have read somewhere that single phase algorithms
can be used - the info given was as follows:

using a single partitioning heirachy
  -bounding volumes hierarchy
  -spatial partitioning such as BSP tree
top levels coarse
  -equivalent to broad phase
lower levels subdivide objects to polygon level
  -equivalent to narrow phase

What I don't understand is whether this actually constitutes using a
narrow phase or whether this is a solution which is only using AABBs
for collision detection.  So, going back to my original question
Is it possible to use ONLY AABBs for collision detection for the
game scenario mentioned above?

Many Thanks


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