[GRASS-dev] G_units_to_meters_factor

Glynn Clements glynn at gclements.plus.com
Thu Sep 22 14:27:44 EDT 2011

Hamish wrote:

> G_units_to_meters_factor() seems to be used by 
>   misc/m.measure/main.c  and  vector/v.to.db/units.c
> which should perhaps follow the location's ultimate source, the
> meters: multiplier from the PERMANENT/PROJ_UNITS file, not its
> own hardcoded calculation!
> for m.measure AFAICT it should definitely be reading from the
> PROJ_UNITS file for the multiplier and not deciding on its own.
> that's a bug.
> for v.to.db, to comes from:
>     parms.units = G_define_standard_option(G_OPT_M_UNITS);
>     parms.units->options =
>         "miles,feet,meters,kilometers,acres,hectares,radians,degrees";
> unless "usfoot" is added to that list, it should always return
> the 0.3048m intl. foot.

How are the units used in v.to.db? For measurements, two parts per
million (four parts per million for areas) probably doesn't matter. 
For coordinates, where you might be several million "feet" from the
origin, it matters.

Glynn Clements <glynn at gclements.plus.com>

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