Re: Double-Precision, Large-Area Databases, and SIGGRAPH

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Michael T. Jones (mtj++at++intrinsic.com)
Wed, 05 May 1999 17:01:38 -0700

At 01:15 PM 5/5/99 -0700, Angus Dorbie wrote:
>This still seems bogus to me.
:
>Bottom line, like I said you still need that modelling manipulation
>between the eye and the terrain cell. You can call it a viewing
>transformation and maybe you'll fool some of the people, but I'm not
>fooled.

Perhaps the problem is confusion about the fact that only
the special tile near the eyepoint avoids relocation in method
B; the other tiles *are* translated using a matrix as in method
A, it's just that the matrix also contains the distance from the
eyepoint to the origin of the local tile. That special tile which
is the closest ("local") tile is the only one not translated since
we use it's local origin as the origin of world space and move
the other tiles and the eyepoint relative to it. (As opposed to
method A which uses the eyepoint as the origin of world space
and moves all terrain tiles relative to the eyepoint.)

Are Angus and I the only ones struggling for clarity here?
If other readers understand then perhaps they can explain
method B more clearly in words than I have. If I had a
markerboard or pen and paper I'm sure that it would be
easier to understand.

Michael "Treasurer-to-be" Jones

----------
Michael T. Jones - <mailto:mtj++at++intrinsic.com>mtj++at++intrinsic.com -
<http://www.intrinsic.com/>Intrinsic Graphics Inc. - (650) 210-9933
SIGGRAPH treasurer candidate: http://www.siggraph.org/elections/index.html
           A frog in a well says "The sky is as big as the mouth of my well"

At 01:15 PM 5/5/99 -0700, Angus Dorbie wrote:

This still seems bogus to me.
:
Bottom line, like I said you still need that modelling manipulation
between the eye and the terrain cell. You can call it a viewing
transformation and maybe you'll fool some of the people, but I'm not
fooled.

Perhaps the problem is confusion about the fact that only
the special tile near the eyepoint avoids relocation in method
B; the other tiles *are* translated using a matrix as in method
A, it's just that the matrix also contains the distance from the
eyepoint to the origin of the local tile. That special tile which
is the closest ("local") tile is the only one not translated since
we use it's local origin as the origin of world space and move
the other tiles and the eyepoint relative to it. (As opposed to
method A which uses the eyepoint as the origin of world space
and moves all terrain tiles relative to the eyepoint.)

Are Angus and I the only ones struggling for clarity here?
If other readers understand then perhaps they can explain
method B more clearly in words than I have. If I had a
markerboard or pen and paper I'm sure that it would be
easier to understand.

Michael "Treasurer-to-be" Jones
Michael T. Jones - mtj++at++intrinsic.com - Intrinsic Graphics Inc. - (650) 210-9933
SIGGRAPH treasurer candidate: http://www.siggraph.org/elections/index.html
          A frog in a well says "The sky is as big as the mouth of my well"

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