Re: Error Ellipse

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
> >
> > To unsubscribe, send the message "signoff gmt-help" to
> [email protected]
>
> To unsubscribe, send the message "signoff gmt-help" to
> [email protected]
>

To unsubscribe, send the message "signoff gmt-help" to [email protected]