[Proj] Numerical Precision in Proj, WKT, and everywhere

Glynn Clements glynn at gclements.plus.com
Fri Apr 2 17:20:00 EST 2010

Gerald I. Evenden wrote:

> > I agree that it's best to avoid unnecessary conversions, but there are
> > many interfaces that require text, such as the proj command-line or OGC
> > web interfaces.  The same issue occurs with the database/application
> > interface with BCD.  We are forced to obey the interfaces of the various
> > systems we wish to chain together.
> BCD? Binary Coded Decimal? Just that I have not heard the term in maybe 25 
> years. Seriously. I am not being sarcastic.

BCD is widely used by software which processes financial data, as
decimal rounding is standard practice and may be required by law
(statute and/or precedent).

Also, if you haven't heard it mentioned in 25 years, I'd have to
suggest that you don't keep track of current events. I've seen fairly
widespread coverage of two specific cases where software thought that
this year was 2016 because of the year being encoded in BCD (the
binary digits 00010000 represent 10 if interpreted as BCD but 16 if
interpreted as binary).

The first case, at the beginning of January, invovled credit/debit
cards failing to work after January 1st due to software thinking that
the cards had expired. The second case involved software thinking that
March 1st was actually February 29th (2016 will be a leap year).


Glynn Clements <glynn at gclements.plus.com>

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