# Re: Office Space ;) and coordinate systems

Thu, 15 Sep 94 17:29:40 EDT

:: From: unitcirc@netcom.com (Kevin Goldsmith)
:: Subject: Re: Office Space ;) and coordinate systems
:: Date: Fri, 9 Sep 1994 22:46:43 -0700 (PDT)
::
:: >
:: > In cartography, once you place a scale on a map, it is accurate even if
:: > enlarged or reduced since the map is reduced or enlarged along with the
:: > scale bar on the map. At the same time a scale notation must be on the
:: > map to indicate what one segment of the scale represents. Such a notation
:: > is all that would be necessary as one item of the VRML object definition
:: > passed in a transaction. Example:
:: >
:: overlapping maps. We want to put them together to get a bigger map. If
:: they are not on the same scale, one of use will have to shrink or blow up
:: our map so that they will be on the same scale. Wouldn't it be easier if
:: they were on the same scale? Or what if we had agreed on a scale and so
:: that we could have blown up or shrunk our maps before we met? This
:: analogy represents what I am talking about.
::
:: Kevin
::

The overlapping maps problem will exist in any case. See below.

:: From: "Gavin Bell" <gavin@krypton.engr.sgi.com>
:: Date: Fri, 9 Sep 1994 13:30:25 -0700
:: Subject: Re: Office Space ;) and coordinate systems
::
:: You're map analogy is reasonable.
::
:: But what if you get maps from 10 different people and you want to paste
:: them together to form one big map?
::
:: Your job will be much, much easier if you don't have to look at all of
:: those scales, figure out how they differ, and spend time at your Xerox
:: machine enlarging or reducing them so they all fit.
::
:: That's what we're trying to avoid by deciding on common units.
::

The 10 maps problem will exist in any case also.

It depends on what you are going to use the scale for. I dont think this
has been fully determined for VRML at this point.

With the 10 maps or the overlapping maps, comparisons would have to be
made between two/many datasets presumably obtained from different places on
the internet. I presently see two possible reasons for this.

1) >merging< datasets together to create a combined world/scene.

2) >linking< datasets to travel from one to the other.

If you have a VRML-standard scale, as suggested in both cases above, then
linking from one set to another(camera movement) would require comparing
them to determine how they relate in scale. The same would be true of a
merging of two datasets. Comparisons would have to take place, right?

For example, suppose you move from an ant-scale world to a human-scale
world. Suppose VRML-standard scale is the same as metric. Ant-scale might
have all objects rendered in millimeters whereas human-scale might have
all objects rendered in centimeters.

Or, perhaps you have a mix of objects. Some are large enough to be in
meters, some are so small as to require millimeter scale. Why state an
object is 1/10 of a meter when centimeters might be a better scale?

In terms of programming algorithms, I see no way around a basic metric
conversion process that converts centimeters to millimeters, kilometers
to meters, etc. in order to place objects within a coordinate system.

If this is the case then why not extend the conversion processing to
allow for any existing unit of measure? All that would be required is
that each VRML object description state the nature of its units in
some known scale. I am thinking of each object being something like
a cube or cone or a more sophisticated 3D object of a stated size.

These objects would be combined by a VR scene designer and -enclosed-
in a bounding object which would in itself be a VRML object.

What matters is the size/scale of the bounding area of the current
object/scene/container. This would be largest object in a transaction,
unless it is Dr Whos TARDIS, of course. :)

VRML would assume that each object definition would have a unit of
measure that defines the size of each 3D object as well as the container.

Conclusion:

I dont think that we need to adopt a standard scale, I think we need to
adopt a unit of measure definition for each object dataset combined
with algorithmic conversion.

```--
Robert K. Foster
Analyst / Designer / Programmer
Mid-Michigan MRI, Inc., Lansing, MI, USA