Re: Expressing physical units (Was: Reprise: 'in out' parameters for functions)

[18k11tm001@sneakemail.com (Russ)]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:<c5dr33$gkic$3@ID-77047.news.uni-berlin.de>...
> Russ wrote:
> 
> > By the way, I work in the field of air traffic management (ATM), and
> > I'd really like to see a practical way to guarantee units consistency.
> > The general mks system is inappropriate for ATM. The traditional units
> > for ATM are nautical miles (nmi) for horizontal length, and feet (ft)
> > for altitude. That won't change in our lifetimes -- and probably
> > never. As for time, it can be in seconds, minutes, or hours.
> > Horizontal speed in usually given in terms of knots (kn), which is
> > nmi/hr, but altitude rate is usually given in terms of ft/min. Heading
> > is normally given in degrees.
> > 
> > In my experience, the most common units problem is confusion between
> > degrees and radians. Radians are preferable for use inside programs,
> > but degrees are preferable for I/O. This problem really needs to be
> > licked once and for all.
> 
> It does not differ from [m] vs. [ft]. The dimension of radian is [1] =
> m**0*A**0*s**0... The dimension of degree is [Pi/180]. No magic here. More
> difficult is Celsius degree vs. K, which AFAIK cannot be solved using C++
> templates.

I know it can be done in C++, but I thought we were talking about doing it in Ada.

By the way, what the heck is "m**0*A**0*s**0..."?

> > The next most common problem I find is that
> > altitude is alternately expressed in terms of ft, hundreds of ft, or
> > thousands of feet. Standard "Flight Levels" are at multiples of 1000
> > ft, but they are expressed in units of 100 ft. For example, "FL310" is
> > a pressure altitude of 31,000 ft.
> 
> See above.