10 Mar
2008
10 Mar
'08
7:25 a.m.
From: "Bob Bradlee" <caveguy at
sbcglobal.net>
Yes of course this is generally true now that we have floating point
built into nearly every processor, but suppose you using say a Pic
chip to process navigational data, I don't think these have floating
point so fixed point would still be useful. For my work when
programming Microspot Interiors (http://www.microspot.co.uk/products/
interiorsPro/index.htm) I mainly use normalised vectors which I find
far better in 3D systems than angles from the axes, but it is horses
for courses. I also work on MacDraft (http://www.microspot.co.uk/
products/macdraft/index.htm) which is an old 2D program, which used
to store angles in fixed point degrees and I have changed to floating
point degrees, but without rewriting a lot of code and possibly
creating bugs, thats as far as I am going. There are issues using 2Pi
because of rounding errors. Usually you end up having tolerance
values. Without tolerances, if someone rotates something by 90
degrees four times, they don't QUITE get what they started with when
using 2PI, but with degrees, they do.
As for representing an infinite number of angles, don't be silly.
Especially if you are using tolerances.
Roger Holmes,
Technical Director, Microspot Ltd.
> Wouldn't that imply that your system
works off of a basis of 256
> degrees
> instead of 360?
>
In this case, 1/262144 of a circle as it was on
an 18 bit computer,
but today you would probably use 32 bits. There's nothing special
about dividing a circle into 360 parts anyway, 420 would have allowed
2PI are Round!
There are 2Pi radians in a circle, very few in the graphics world
use interger degrees for anything other
than human readable or heman generated I/O. A line is bounded by 2
points or can be described as a
angle and distance from a relitave point. While Arc's can be
specified by a start, end, and center point,
Curves are almost always specified in radians. Autodesk had an
interesting bulge value.
In the graphics world 2 pi are round and can represent an infinate
number of angles, and truely not
square :) 
10 Mar
10 Mar
3:08 p.m.
On Mon, 10 Mar 2008 11:25:55 +0000, Roger Holmes wrote:
There are issues using 2Pi
because of rounding errors. Usually you end up having tolerance
values. Without tolerances, if someone rotates something by 90
degrees four times, they don't QUITE get what they started with when
using 2PI, but with degrees, they do.
Were are not talking about rotating an image here just projecting one.
As for representing an infinite number of angles,
don't be silly.
Especially if you are using tolerances.
Point taken :-)
You also pointedout corredtly that floating point hardware was not always available.
We were punching fixed-point CAD data on 80 col cards and plotting bed sheets on a
flatbead plotter, it
was "old" when I first worked with it in the mid 70's at Western Electric.
BTW: radians work fine with fixpoint provided you are not rotating things that were
previously rotated.
Back to topic, I think the subject was displaying tesx on a vector screen.
In the 1960's Dr. A.V. Hershey of the Naval Weapons Laboratory while working with the
U. S.. National
Bureau of Standards created the Hershey's Repertory of Occidental Type Fonts. This is
the origional data
set I used when I built the CADfont set for AutoCAD that became the extened font set and
package with
the product.
Over the years many conversions/translations have been made, somewhere around here I have
a copy
coded in (lisp) for driving a flame cutter. Check it out, and yes it is interger vector
based ....
Here is a google link for more info:
http://tinyurl.com/36un8h
Back under my rock ...
Bob
11 Mar
11 Mar
12:21 a.m.
From: caveguy at sbcglobal.net
On Mon, 10 Mar 2008 11:25:55 +0000, Roger
Holmes wrote:
Hi
This is a common problem for most math functions.
One of the problem is rounding to zero ( bad idea for
continuous number lines with positive and negative values ).
Floor math doesn't usually have such problems.
Dwight
_________________________________________________________________
Shed those extra pounds with MSN and The Biggest Loser!
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There are issues using 2Pi
because of rounding errors. Usually you end up having tolerance
values. Without tolerances, if someone rotates something by 90
degrees four times, they don't QUITE get what they started with when
using 2PI, but with degrees, they do.
Were are not talking about rotating an image here just projecting one.
5954
days inactive
5955
days old
2 comments
3 participants
participants (3)
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caveguy＠sbcglobal.net -
dkelvey＠hotmail.com -
roger.holmes＠microspot.co.uk