RE: Re[2]: [cgmo-webcgm] Re:

["Dieter Weidenbrueck" <dieter@itedo.com>]

Hi Benoit,

>-----Original Message-----
>From: Benoit Bezaire [mailto:benoit@itedo.com]
>Sent: Thursday, July 08, 2004 9:36 PM
>To: Dieter Weidenbrueck
>Cc: Lofton Henderson; cgmo-webcgm@lists.oasis-open.org
>Subject: Re[2]: [cgmo-webcgm] Re:
>
>
>DW> The coordinate system should be described as follows:
>
>DW> width = resulting mm width of VDC extent
>DW> height = resulting mm height of VDC extent
>Could I please get a pointer to read on how "resulting mm width/height
>of VDC extent" gets computed?

>From CGM:1999:
"6.4.1 Scaling mode
VDC space may be either an abstract space, which may be mapped to an
arbitrary size on a physical device, or a metric space, which is intended to
be mapped to a particular size. Selection of the mode to be used can be made
on a picture-by-picture basis by means of the SCALING MODE element. The
scaling mode element provides a flag to select abstract space or metric
space, and a scale factor which specifies the number of millimeters per VDC
unit when metric space is selected."

For WebCGM, the scaling mode is always metric, the scale factor may vary.
The VDC (Virtual Device Coordinates) extent is expressed in VDC coordinates.
The VDC coordinates depend on the VDC type (integer 16 or 32 bit, or real),
and the scalemode.
Thus the resulting coordinates on a "metric device" are recognized as real
or
integer first (depending on the VDC TYPE), and then scaled using the factor
specified by the SCALING MODE.
If you need more, look for the sections on VDC extent, VDC type, and scaling
factor
in CGM:1999.

>
>DW> Origin:
>DW> lower left corner of VDC extent
>DW> coordinates at origin: 0,0
>DW> top left coordinates: width,height (or 100%,100% where applicable)
>What does "or 100%, 100% where applicable" mean, where would it be
>applicable?

I thought we had discussed to express coordinates of a hotspot either in
mm or in %. I am certainly happy with mm only to keep it simple.

Regards,
Dieter