[GRASS-dev] area measurements

[Anna Petrášová]

Hi all,

I added support for area measurement in wxGUI (the same place as measuring
distance). You are welcome to test. However, I have a few
questions/problems:

I was wondering if module m.measure requires a series of coordinates with
or without repeating the first pair of coordinates. This is suggested by
the fact that it requires at least 4 points for measuring area. If I
suppress this condition and use only 3 points it gives me the right result,
too.
This is probably given by the underlying functions G_area_of_polygon, but I
haven't found anything in the documentation. I would be glad if we can
write something in the m.measure manual because the user might be surprised
not to get area for 3 points.

The second thing is about projection. For this projection:

name=Lambert Conformal Conic
proj=lcc
datum=nad83
a=6378137.0
es=0.006694380022900787
lat_1=34.33333333333334
lat_2=36.16666666666666
lat_0=33.75
lon_0=-79
x_0=609601.2199999997
y_0=0
no_defs=defined
unit=Foot_US
units=Foot_USs
meters=0.3048006096012192

I get nothing from m.measure. I can create a ticket if necessary.

Best,

Anna


On Mon, Dec 30, 2013 at 7:50 AM, Markus Neteler <neteler at osgeo.org> wrote:

> On Sat, Dec 28, 2013 at 3:28 PM, Vincent Bain <bain at toraval.fr> wrote:
> > Hello dear devs,
> >
> > I am wondering if something happened since this 4 year old ticket, where
> > the question of area measurements was raised :
> >
> > http://trac.osgeo.org/grass/ticket/975
> >
> > When I need to get an area on the fly, I run d.measure on a graphic
> > monitor, but it would be very nice to access this function straightly
> > from wxGUI. Using 6.4 for my workflow, perhaps I missed something on the
> > 7.0 side ?
>
> In the ticket m.measure is suggested as solution which accepts a
> series of coordinates to then perform the calculation:
> http://grass.osgeo.org/grass70/manuals/m.measure.html
>
> Perhaps, given that a new tiny digitizer is there for wxGUI-i.class
> etc, perhaps this could be used to call m.measure then?
>
> > Thank you, and best wishes for New Year's Eve ;-)
>
> Thanks & best wishes from here,
> Markus
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