From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,9d303864ae4c70ad X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2004-04-12 03:29:58 PST Path: archiver1.google.com!news2.google.com!fu-berlin.de!uni-berlin.de!dialin-145-254-037-237.arcor-ip.NET!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Expressing physical units (Was: Reprise: 'in out' parameters for functions) Date: Mon, 12 Apr 2004 12:29:26 +0200 Organization: At home Message-ID: References: <5ad0dd8a.0404090512.15af2908@posting.google.com> <5ad0dd8a.0404100507.729d3577@posting.google.com> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: dialin-145-254-037-237.arcor-ip.net (145.254.37.237) Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit X-Trace: news.uni-berlin.de 1081765796 545356 I 145.254.37.237 ([77047]) User-Agent: KNode/0.7.2 Xref: archiver1.google.com comp.lang.ada:6995 Date: 2004-04-12T12:29:26+02:00 List-Id: 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. > 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. -- Regards, Dmitry A. Kazakov www.dmitry-kazakov.de