[ncl-talk] gc_inout for non-spherical polygons?

[Dave Allured - NOAA Affiliate]

Nisha,

There is more than one way to define a square or rectangle on the surface
of the earth.  They are mathematically and geographically different.

1.  You can define a rectangle by its four corner points, with the edges
defined as great circle lines between the four corners.  This defines a
spherical polygon.  gc_inout is the correct way to handle a polygon defined
this way.

2.  You can define a rectangle by its four corner points, connected by
straight lines in cartesian coordinate space (i.e. lat/lon space).  A
simple example would be the area between 30 to 35 degrees north, and 80 to
100 west.  gc_inout would NOT give correct results for this definition.

There may be other ways as well.  A "rectangle" could be defined as a
region enclosed by four straight lines, drawn over the surface of the earth
in any map projection, of which there are many.

Which definition do you have in mind?

--Dave


On Mon, Nov 9, 2015 at 2:57 PM, Manisha Ganeshan <
manisha.ganeshan86 at gmail.com> wrote:

> Hi,
>
> I'm wondering if a function like gc_inout can work for other polygons,
> specifically square/rectangle?
>
> Regards,
> Nisha
>
> --
> Dr. Manisha Ganeshan
> Universities Space Research Association
> Maryland, U.S.A.
>
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