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From: Stephen Leake <Stephe.Leake@nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Logic Errors and Ada (Was: A big hairy thread on Ada, Quality,
 and Drivers)
Date: 20 May 2003 09:36:04 -0400
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Preben Randhol <randhol+abuse@pvv.org> writes:

> Dr Chaos wrote:
> > On 19 May 2003 20:42:42 +0100, Simon Wright <simon@pushface.org> wrote:
> >>   type Position is record
> >>      Lat  : Latitude;
> >>      Long : Longitude;
> >>   end record;
> >> 
> >> and inspect the low-level support subprograms.
> > 
> > What is the right way to do spherical geometry with separate
> > latitude and longitude types?
> > 
> > The problem mathematically that I see is that SO(3) 
> > transformations will yield arithmetic combinations of these,
> > which would require lots of I would guess conversions to
> > some kind of default float.
> 
> Maybe so (I don't know), but would it not be a bigger chance of catch
> lunatic calculations when you try to do a conversion back to Latitude
> and Longitude? I mean if the values are outside the bounds of the
> Latitude and Longitude types?
> 
> > On the other hand, if Latitude and Longitude were variables
> > whose values would be displayed to humans or perhaps stored
> > in some database, then the separate typing may work. 
> 
> Huh?

I think he agrees with my policy; do all internal calculations in a
data structure that supports full rotations (SO(3) is group theory
notation for the rotation group); that means orthornormal matrices or
unit quaternions. Only convert to lat/long for user input/output. That
avoids singularities and unit confusion in the core code.

-- 
-- Stephe