.. _example_26:

(26) General vertical perspective projection
--------------------------------------------

Next, we present a recent extension to the **-JG** projection option
which allows the user to specify a particular altitude (this was always
at infinity before), as well as several further parameters to limit the
view from the chosen vantage point. In this example we show a view of
the eastern continental US from a height of 160 km. Below we add a view
with a specific tilt of 55 and azimuth 210; here we have chosen a
boresight twist of 45. We view the land from New York towards
Washington, D.C.

At this point the full projection has not been properly optimized and
the map annotations will need additional work. Also, note that the
projection is only implemented in
:doc:`pscoast </pscoast>` and
:doc:`grdimage </grdimage>`. We hope to refine this
further and extend the availability of the full projection to all of the
GMT mapping programs.

.. literalinclude:: /_verbatim/example_26.txt
   :language: bash

.. figure:: /_images/example_26.*
   :width: 500 px
   :align: center

   General vertical perspective projection.