.. _example_09:

(9) Time-series along tracks
----------------------------

A common application in many scientific disciplines involves plotting
one or several time-series as as "wiggles" along tracks. Marine
geophysicists often display magnetic anomalies in this manner, and
seismologists use the technique when plotting individual seismic traces.
In our example we will show how a set of Geosat sea surface slope
profiles from the south Pacific can be plotted as "wiggles" using the
:doc:`wiggle </wiggle>` program. We will embellish
the plot with track numbers, the location of the Pacific-Antarctic
Ridge, recognized fracture zones in the area, and a "wiggle" scale. The
Geosat tracks are stored in the file ``tracks_09.txt``, the ridge in ``ridge_09.txt``, and all the
fracture zones are stored in the multiple segment file ``fz_09.txt``. The
profile id is contained in the segment headers and we wish to use the
last data point in each of the track segments to construct an input file
for :doc:`text </text>` that will label each profile
with the track number. We know the profiles trend approximately N40E so
we want the labels to have that same orientation (i.e., the angle with
the baseline must be 50). We do this by extracting the last record from
each track and select segment header as textstring when running
the output through :doc:`text </text>`. Note we
offset the positions by 4 points with **-D** in order to have a small
gap between the profile and the label:

.. literalinclude:: /_verbatim/ex09.txt
   :language: bash

The output shows the sea-surface slopes along 42 descending Geosat
tracks in the Eltanin and Udintsev fracture zone region in a Mercator projection.

.. figure:: /_images/ex09.*
   :width: 500 px
   :align: center

   Time-series as wiggles along a track.
