Satellite positioning with GPS is the dominant method of surveying throughout the world. For high-accuracy surveying, relative positioning prevails; two receivers gather data at the same time and the difference in position between the receivers is calculated.
It's a rare occasion when I write about something other than GPS, but not long ago I was reminded that surveyors should not pay so much attention to technology that they forget the basic principles of surveying, and I wanted to share this important reminder with POB's readers.
I have a two-part question. I have a total station setting for curvature and refraction correction. To turn it on, I have to select from one of two constants to be used in the correction. Which one should I be using? The second part of my question comes from noticing that my surveying textbook (Moffit & Bossler) uses only one constant for the curvature and refraction correction. Why the difference?
As I have reported in previous GPS Observer columns (POB November 2004, December 2005), the National Geodetic Survey (NGS) is in the process of readjusting the National Spatial Reference System (NSRS). This will be the first-ever three-dimensional national adjustment. Detailed information about this readjustment is available on the NGS website at www.ngs.noaa.gov. In addition to readjusted coordinates, the output of the readjustment will be an accuracy value at the two standard deviations (2Ïs) level for each component of the station's position. Since the detailed information on the format of the data sheet has not been published, this gives me leeway to speculate on what will happen.
When the target centering feature of my servo-driven total station is switched on and I do a visual check through the telescope, I often find that the telescope cross hairs are not on the target. There seems to be a constant offset above and to the left of the target. My instrument dealer has told me not to worry about this. He says that the instrument has been calibrated and that a software correction is applied. Is this true? Should I be concerned?