Re: Error Ellipse

I assume his degrees are great circle distances in degrees for major and minor axes.  Otherwise it would be very odd.
-p


On Nov 28, 2013, at 3:11 PM, keithpickering . <[email protected]> wrote:

> Multiplying by a fixed number works OK with the y-axis (latitude) but the x-axis (longitude) is latitude dependent. In that case, you will need to compute cosine(latitude) * degreesLongitude * 111.95 to get km. This can be done directly in the Unix/Linux command line environment using bc, if all else fails.
> 
> Keith Pickering
> 
> 
> On Thu, Nov 28, 2013 at 5:27 PM, Paul Wessel <[email protected]> wrote:
> Hi Jay-
> 
> You need to scale those degrees to km on the sphere.  Probably good enough to multiply by 111.195.
> Either use awk to do this, or in GMT 5 just use -i0-2,3s111.195,4s111.195 when reading your lon,lat,az,major,minor file.
> 
> You may also want to file a feature request on the gmt site for psxy to handle degrees as an option.
> 
> -p
> 
> 
> On Nov 28, 2013, at 12:50 PM, Shah, Jay <[email protected]> wrote:
> 
> > Hello,
> >
> > I would like to plot points on a map, including error ellipses computed using known separate errors in degrees in latitude and longitude.  Obviously the points on the map are easy via psxy, but precisely how to plot the ellipses (with major and minor axes measured in degrees) is unclear to me.  For example, I have tried using psxy with the -SE option, but the error bars require plotting in distances, not degrees.
> >
> > I would be most grateful if anyone could point me in the right direction with this.  Perhaps psxy -SE....is not the right approach to take?
> >
> > Best Wishes,
> >
> > Jay
> >
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> 
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