Re: [boost] [Review][PQS] Review deadline

From: Gerhard Wesp (gwesp_at_[hidden])
Date: 2006-06-07 04:51:11

Sorry, I don't have the time to read the PQS documentation in-depth
right now.

Still, I'd like to make one suggestion.

I think that handling of dimensional quantities and conversion factors
are orthogonal concepts and should be separated.

I suggest that for maximum transparency the library should *exclusively*
handle quantities expressed in SI units.

I'm aware that this "mildly forces" developers to adopt SI units.  I
consider this a Good Thing.

Conversion factors between non-SI units and SI units should be constant
dimensional quantities, e.g. (assuming constructors from double):

const length foot                 =    .3048 ;  // Meter
const power  european_horse_power = 735.4987 ;  // Watt
const mass   pound                = 0.4535924;  // Kilogram
// ...

This way, one could e.g. construct dimensional quantities like this:
const power deux_chevaux = 2 * european_horse_power;

Non-SI quantities would have to stay "out of the system" in normal
floating point variables:

length altitude;
double altitude_ft = altitude / foot;

Ignoring dimensionality, this is the notation Mathematica chooses.

I have done some engineering simulations, written a flight simulation
framework and used one that uses US units (D6; see www.bihrle.com).  The
D6 source code is riddled with magic constants.  I've collected some
conversion constants in units.h of cpp-lib, see
http://gwesp.tx0.org/software/.

Regards
-Gerhard
-- 
Gerhard Wesp
ZRH office voice: [phone]
ZRH office fax: [phone]
For the rest I claim that raw pointers must be abolished.