Re: how to calculate the area of polygon?

Paul
Thank you very much for your quick and kind reply.
regards,
takaya

> Date: Thu, 5 Dec 2013 17:51:34 -1000
> From: [email protected]
> Subject: Re: [GMT-HELP] how to calculate the area of polygon?
> To: [email protected]
> 
> gmtspatial -Q will either compute areas for closed polygons or line length for unclosed lines.  Your polygon is not closed so it is assumed to be a line and you get the length of the line and its mid point.
> We may want to add a modifier to "force closure of lines to make polygons" but it is not there yet.
> If I close your polygon then I get
> 
> gmtspatial poly.data -Q
> 15	-55	100
> 
> assuming cartesian data and
> 
> gmtspatial poly.data -Q -fg
> 15	-55.1025678246	707841.648502
> 
> if I tell it the data are geographic.
> 
> On Dec 5, 2013, at 2:43 PM, Namba Takaya <[email protected]> wrote:
> 
> > Dir Sir
> > 
> > According to your suggestion, 
> > 
> > I tried to do the script below to calculate the area of the polygon with gmtspatial, but the result is strange as unexpected.
> > 
> > Could you tell me how to solve the problem?
> > 
> > gmtspatial poly.data -Q
> > 
> > poly.data is like
> >  20:00  -50:00
> >  20:00  -60:00
> >  10:00  -60:00
> >  10:00  -50:00
> > 
> > regards,
> > 
> > takaya
> > 
> > Date: Thu, 28 Nov 2013 15:48:05 +0100
> > From: [email protected]
> > Subject: Re: [GMT-HELP] how to calculate the area of polygon?
> > To: [email protected]
> > 
> > In GMT5 you can do this using gmtspatial, 
> > 
> > If you are stuck with GMT4 it should be possible to do so using grdvolume if you first define a grid file in which all the points inside your polygon has a constant value differing from the points outside, then apply grdcontour to the countour value equal to the value you have chosen inside your polygon.  
> > 
> > regP 
> > 
> > 
> > On 11/28/2013 03:35 PM, Namba Takaya wrote:
> > Dear sir
> > 
> > 
> > Could you tell me how to calculate the area of polygon(hour points) like
> > 
> > 1.   5:00E  55:00S 
> > 2.   6:00E  55:00S
> > 3.   6:00E  56:00S
> > 4.   5:00E  56:00S
> > 
> > regards,
> > 
> > takaya
> > 
> > -- 
> > ********************************************************************************
> > Peter Schmidt                                      Tel: +46-18-4717104
> > Swedish National Seismological Network (SNSN)   Mobile: +46-73-3190975
> > Dept. of Earth Sciences:geophysics              e-mail: 
> > [email protected]
> >   
> > Uppsala University
> > Villavagen 16
> > SE-75236 Uppsala
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