[GRASS-dev] Re: output precision of r.info and r.univar

[Markus Neteler]

On Wed, Oct 8, 2008 at 9:48 AM, Markus Neteler <neteler at osgeo.org> wrote:
> Hi,
>
> to gain more precision when using r.info -r and r.univar -g output in
> scripts, I want to suggest this change:
>
> Index: r.info/main.c
> ===================================================================
> --- r.info/main.c       (revision 33591)
> +++ r.info/main.c       (working copy)
> @@ -330,8 +330,8 @@
>                }
>            }
>            else {
> -               fprintf(out, "min=%f\n", zmin);
> -               fprintf(out, "max=%f\n", zmax);
> +               fprintf(out, "min=%.10f\n", zmin);
> +               fprintf(out, "max=%.10f\n", zmax);
>            }
>        }
>
> Index: r.univar2/stats.c
> ===================================================================
> --- r.univar2/stats.c   (revision 33591)
> +++ r.univar2/stats.c   (working copy)
> @@ -110,14 +110,14 @@
>     if (param.shell_style->answer) {
>        fprintf(stdout, "n=%d\n", stats->n);
>        fprintf(stdout, "null_cells=%d\n", stats->size - stats->n);
> -       fprintf(stdout, "min=%g\n", stats->min);
> -       fprintf(stdout, "max=%g\n", stats->max);
> -       fprintf(stdout, "range=%g\n", stats->max - stats->min);
> -       fprintf(stdout, "mean=%g\n", mean);
> -       fprintf(stdout, "mean_of_abs=%g\n", stats->sum_abs / stats->n);
> -       fprintf(stdout, "stddev=%g\n", stdev);
> -       fprintf(stdout, "variance=%g\n", variance);
> -       fprintf(stdout, "coeff_var=%g\n", var_coef);
> +       fprintf(stdout, "min=%.10f\n", stats->min);
> +       fprintf(stdout, "max=%.10f\n", stats->max);
> +       fprintf(stdout, "range=%.10f\n", stats->max - stats->min);
> +       fprintf(stdout, "mean=%.10f\n", mean);
> +       fprintf(stdout, "mean_of_abs=%.10f\n", stats->sum_abs / stats->n);
> +       fprintf(stdout, "stddev=%.10f\n", stdev);
> +       fprintf(stdout, "variance=%.10f\n", variance);
> +       fprintf(stdout, "coeff_var=%.10f\n", var_coef);
>        fprintf(stdout, "sum=%s\n", sum_str);
>     }
>     else {
>
> --------------
> Before:
> r.info -r tmp1
> min=0.000002
> max=75.527772
>
> r.univar -g mymap | grep min | cut -d'=' -f2
> 2.72222
>
>
> After:
> r.info -r tmp1
> min=0.0000020898
> max=75.5277723706
>
> r.univar -g mymap | grep min | cut -d'=' -f2
> 2.7222220898
>
> Any objections?

I just found Glynn's comment:

On Wed, Oct 8, 2008 at 9:36 AM, Glynn Clements <glynn at gclements.plus.com> wrote:
...
> Too much precision is ugly. Too little precision makes it impossible
> to use small values. A general-purpose conversion routine such as this
> needs to handle the full range of floating-point values, which
> basically means %.15g.

So should I go for that?

Markus