[GRASS5] Interfaces ... (long)

[Helena]

Glynn Clements wrote:

> Another issue related to G_parser() is those programs which initialise
> options dynamically (either their default values, allowable values or
> descriptions).
>
> These seem to fall into a number of specific cases:
>
> 1. D_get_cell_name (d.colors), D_get_{cell,dig,site}_list (several
> programs) and other functions (d.save) to obtain state from the
> monitor.
>
> 2. G_gisbase, G_mapset, G_projection, G_zone, G_get_window and
> G_get_set_window to obtain information about the current location.
>
> 3. spheroid_list and datum_list. In the case of spheroid_list, many
> programs implement this function independently.
>
> 4. G_{lat,lon}_format_string, D_color_list. These functions actually
> just return string literals.
>
> 5. read_list (used by g.{copy,list,remove,rename} to parse
> etc/element_list).
>
> Case 1 is problematic as they will fail (even for "help" and
> int.desc.) if the there is no monitor running, although Eric (I think)
> appears to fixing that.
>
> Both cases 1 and 2 are problematic in that they generate help messages
> or interface descriptions which depend upon the context in which they
> are run. For example, v.surf.rst does this:
>
>   if (G_get_set_window (&cellhd) == -1)
>     exit (0);
>   ew_res = cellhd.ew_res;
>   ns_res = cellhd.ns_res;
>         ...
>   if (ew_res < ns_res)
>     dmin = ew_res / 2;
>   else
>     dmin = ns_res / 2;
>         ...
>   sprintf (dmaxchar, "%f", dmin * 5);
>   sprintf (dminchar, "%f", dmin);
>         ...
>   parm.dmax->answer = dmaxchar;
>         ...
>   parm.dmin->answer = dminchar;
>
> The result is that "v.surf.rst help" says (amongst other things):
>
>         Parameters:
>              input   Name of the vector file with input data
>               dmax   Maximum distance between points
>                      default: 250.000000
>               dmin   Minimum distance between points
>                      default: 50.000000
>
> It should, IMHO, at least provide some indication that these defaults
> are for the current location e.g.:
>
>               dmin   Minimum distance between points
>                      default: 50.000000 (Dynamic)
> or even
>               dmin   Minimum distance between points
>                      default: min(ew_res,ns_res)/2

 or even better
                          default: 50.000000, min(ew_res,ns_res)/2
          or                            50.000000, half the cell size
(for those who may not know what ew_res means)

because often when I run help I would like to know what the default
would be for my particular region/resolution. but there are also
situations
when the user wants to know what the command does in general - and
then it would be good to know that it depends on resolution.
When this was set up we idealistically assumed that everybody who wants
to use this program will read the manual where the default is described.
I guess that this should be considered for 5.1???

Helena

>
>
> Cases 3, 4 and 5 don't appear to cause these problems, as the values
> used seem to be constant. However, they do seem to point to an area
> where it might be worth extending G_parser.
>
> Some of these suggest that it might be worth the parser supporting
> certain specific types, e.g. from case 2, "projection" and "zone",
> from case 3, "spheroid" and "datum", and from case 4 "color" [sic ;)].
> It also suggests that spheroid_list should be included into libgis.
>
> The programs which use G_{lat,lon}_format_string tend to insert the
> format string into an argument's "description" field with sprintf().
> This leads me to wonder whether it might be worth G_parser()
> supporting "macros" in the description field for this sort of thing.
>
> --
> Glynn Clements <glynn.clements at virgin.net>
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