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

[Helena]

Glynn Clements 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.
When we discussed the impementation of FP in GRASS it was obvious that for
most of the applications at that time 7 digits were sufficient, however, with
GIS
being increasingly used to support numerical modeling the precision needed can
easily exceed FP. On the other hand, handling everything as DCELL would be
overkill
as most of the current data are indeed sufficiently supported by FP.
Some of the print outs - e.g. for r.colors with the rules option have really a
ridiculously
large number of digits which may be confusing for many users so it would be
useful
to change the output at least for those cases where the solution is obvious.

Helena

>
>
> --
> Glynn Clements <glynn.clements at virgin.net>
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