Getting PDOP, VDOP and HDOP in C

[David Taylor]

I have a program which returns a valid gps_data_t named gps_data.  My knowledge 
and reading of the headers isn't good enough to find how to get the three 
variables: pdop, hdop and vdop, although I suspect they are available.  Could 
some kind soul show me how, please?

given in outline:

  struct gps_data_t gpsdata;
  status = gps_open (GPSD_SHARED_MEMORY, DEFAULT_GPSD_PORT, &gpsdata);
  gps_read (&gpsdata, NULL, 0);

  hdop = gpsdata.<what>
  vdop = gpsdata.<what>
  pdop = gpsdata.<what>

Thanks,
David
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