.. _example_02:

(2) Image presentations
-----------------------

As our second example we will demonstrate how to make color images from
gridded data sets (again, we will defer the actual making of grid files
to later examples). We have prepared two 2-D grid files of bathymetry and
Geosat geoid heights from global grids and will put the two images on the
same page. The region of interest is the Hawaiian Islands, and due to
the oblique trend of the island chain we prefer to rotate our
geographical data sets using an oblique Mercator projection defined by
the hotspot pole at (68W, 69N). We choose the point (190, 25.5) to be
the center of our projection (e.g., the local origin), and we want to
image a rectangular region defined by the longitudes and latitudes of
the lower left and upper right corner of region. In our case we choose
(160, 20) and (220, 30) as the corners. We twice use
:doc:`grdimage </grdimage>` to make the illustration:

.. literalinclude:: /_verbatim/ex02.txt
   :language: bash

We again set up a 2 by 1 subplot layout and specify the actual region and
map projection we wish to use for the two map panels.
We use :doc:`makecpt </makecpt>` to generate a linear color
palette file ``geoid.cpt`` for the geoid and use
:doc:`grd2cpt </grd2cpt>` to get a histogram-equalized
CPT ``topo.cpt`` for the topography data.  We run
:doc:`grdimage </grdimage>` to create a color-coded image
of the topography, and to emphasize the structures in the
data we use the slopes in the north-south direction to
modulate the color image via the **-I** option. Then, we place a color legend to the right of the
image with :doc:`colorbar </colorbar>`. We repeat these steps for the
Geosat geoid grid. Again, the labeling of the two plots with a)
and b) is automatically done by :doc:`subplot </subplot>`.

.. figure:: /_images/ex02.*
   :width: 500 px
   :align: center

   Color images from gridded data.
