.. _add_btpoints:

Adding more Bottom Track points if the ship was slow
-------------------------------------------------------

**Question:**

I have a UHDAS+CODAS Python processing directory with a high-frequency
instrument, in shallow water, and almost no bottom track points are
avaliable.  How do I increase the number of bottom track points?

**Answer:**

Bottom tracking calibration consists of 3 steps, all in cal/botmtrk
By default:

 (1) ``lst_btrk lst_btrk.tmp``      # by default: whole cruise, run once
 (2) ``refabs refabsbt.tmp``        # by default: whole cruise, run once
 (3) ``python3 Btplot_script.py``    # this has things to configure

See (bottom) for an example of the original file, and below is
the 'diff' showing what I changed to reduce acceptable ship speed
cutoff and more importantly) decrease minimum allowable depth.   This
is bottom depth, so in this example the hull is 3m down and the instrument
is BB600.  For an OS150 with 8m bins, you might reduce it from 25 to 15m,
but shallower than that would not make sense.::

 >    min_speed  = 1,    # not default
 >    min_depth  =  7,   # not default
 >    outfilebase = 'btcal_more',  # not default

Don't forget the comma at the end of each line: the '#' is a comment
and everything after that is ignored.

Take a look at the new file (below).  Note all the (undocumented) parameters
in the commented section at the top of the file.  Note where the "min_speed",
"min_depth", and "outfilebase" are listed at the top.  There are other parameters
one might change, but these are the usual things to change for this purpose.

**Instructions:**

 - Copy ``Btplot_script.py`` to a new name (``Btplot_script_morepts.py``)
 - Edit (as below) for your case
 - Run as "``python3 Btplot_script_morepts.py``"


Example::


 #---------------- new file Btplot_script_morepts.py ------
 #!/usr/bin/env python

 ## written by quick_mplplots.py -- edit as needed:

 ## cruiseid      is 'ADCP'
 ## dbname        is 'aship'
 ## proc_yearbase is 2013
 ## printformats  is 'png'

 import matplotlib.pyplot as plt

 from pycurrents.adcp.quick_mplplots import Btplot

 ## other parameters that can be chosen:
 ##   name            default
 ##   ------        --------------
 ##   dbname           (found in ../../adcpdb)
 ##   titlestr         (uses ADCP
 ##   proc_yearbase    (first year in database)
 ##   printformats               'pdf'
 ##   dpi                        100
 ##   outfilebase               'btcal'
 ##   ddrange                    'all'  # [223.4, 225.5]
 ##   step                       1
 ##   min_speed                  2
 ##   max_sig                    2.5
 ##   max_gap                    0.1
 ##   tol_dt                     0.02
 ##   min_depth                  25                #shallower for high freq
 ##   max_depth                  1500
 ##

 BT = Btplot()
 BT(btm_filename='aship.btm',
    ref_filename='aship.ref',
    cruiseid = 'ADCP',
    printformats = 'png',
    min_speed  = 1,    # not default
    min_depth  =  7,   # not default
    outfilebase = 'btcal_more',  # not default
    proc_yearbase='2013')

 plt.show()

 #-------------- end of file --------------



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