SUAZIMUTH - compute trace AZIMUTH given the sx,sy,gx,gy header fields and set a user-specified header field to this value

suazimuth <stdin >stdout [optional parameters]

Required parameters:
none

Optional parameters:
key=otrav header field to store computed azimuths in
scale=1.0 value(key) = scale * azimuth
az=0 0-179.9999 deg convention, reciprocity assumed
=1 0-359.999 deg convention, points from source
to receiver
sector=1.0 if set, defines output in sectors of size
sector=degrees_per_sector, the default mode is
the full range of angles specified by az
Notes:
The value of header word "key" is computed from the values of
sx,sy,gx,gy. The output field "otrav" was chosen arbitrarily as an
example of a little-used header field, however, the user may choose
any field that is convenient for his or her application.

Setting the sector=number_of_degrees_per_sector sets key field to
sector number rather than an angle in degrees.

For az=0, azimuths are measured from the North, however, reciprocity
is assumed, so azimuths go from 0 to 179.9999 degrees. If sector option
is set, then the range is from 0 to 180/sector.

For az=1, azimuths are measured from the North, with the assumption that
the direction vector points from the receiver to the source, no
reciprocity is assumed, so the angles go from 0 to 359.999 degrees.
If the sector option is set, then the range is from 0 to 360/sector.

Type: sukeyword -o to see the keywords and descriptions of all
header fields.

To plot midpoints, use: su3dchart


Credits:
based on suchw, su3dchart
CWP: John Stockwell and UTulsa: Chris Liner, Oct 1998

Algorithm:
midpoint x value xm = (sx + gx)/2
midpoint y value ym = (sy + gy)/2

Azimuth will be defined as the angle, measured in degrees,
turned from North, of a vector pointing to the source from the midpoint,
or from the midpoint to the source. Azimuths go from 0-179.000 degrees
or from 0-180.0 degrees.

value(key) = scale*[90.0 - (180.0/PI)*(atan((sy - ym)/(sx - xm))) ]
or
value(key) = scale*[180.0 - (180.0/PI)*(atan2((ym - sy),(xm - sx)) ]

Trace header fields accessed: sx, sy, gx, gy, scalco.