[GRASS5] Re: [GRASS_DE] r.mapcalc round()

[Roger Bivand]

On Thu, 7 Jun 2001, Glynn Clements wrote:

> 
> Helena wrote:
> 
> > > Also, I'm not sure if there's much point having separate defaults for
> > > FCELL and DCELL data. Does anyone know of real-world cases where the
> > > actual precision exceeds that of "float" (rel. error ~= 1.2e-7)?
> > 
> > It is safe to assume that such data exist. Even with the accuracy of
> > the current elevation measurements in cm you want the data stored
> > with precision in mm and in higher elevation areas you would need 7
> > digits. It is even more important for data such as curvatures or
> > pollutant concentrations which can change over several magnitudes.
> 
> The bottom line is whether the cases where DCELL data really warrant
> greater precision are sufficiently common to justify doing the extra
> work involved at the present time (i.e. before 5.0.0 is released).
> 
> Something needs to be done now, as there is existing code (unless it's
> all been changed since the start of this discussion) which will
> sometimes do the wrong thing (specifically, use of "%f" or "%.<fixed
> precision>f", which will introduce significant error for small
> values), with no way for the user to change it.
> 
I agree that this 5.0.0 solution is the one to go for now, because it
permits us to set the environment variable to cater for other cases if
need be. I'm unsure about whether there is a help page giving the
environment variables and their default settings - if there is, that would
be where to put the info, and maybe also a standard phrase on affected
program pages?

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no
and: Department of Geography and Regional Development, University of
Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.