Never used control point
Or at least there is a very low probability it was ever used.
One of many.
Survey point nail hammered into tree stub and marked with red spray and ribbon. Surveyed with a Leica 300 or 1200 series GPS using RTK, two times some hours apart.
After a while one learned to disregard any measurements with a PDOP* higher than 3 or 4... The accuracy we where going for was 5 cm (about 2 in) (1 sigma), if we did not get within that on the second survey we did a third and so on.
* PDOP (Position, dilution of precision) is a bit simplified an estimate of how accurate the 2D position measurement is. It depends on how well spread out the GPS satellites are, and surprisingly much on the time of day (it is much better in the morning). My guess is that during the day the sun excites the ionosphere which already before that is one of the largest contributors to the GPS measurement error.
Never used control point
Or at least there is a very low probability it was ever used.
One of many.
Survey point nail hammered into tree stub and marked with red spray and ribbon. Surveyed with a Leica 300 or 1200 series GPS using RTK, two times some hours apart.
After a while one learned to disregard any measurements with a PDOP* higher than 3 or 4... The accuracy we where going for was 5 cm (about 2 in) (1 sigma), if we did not get within that on the second survey we did a third and so on.
* PDOP (Position, dilution of precision) is a bit simplified an estimate of how accurate the 2D position measurement is. It depends on how well spread out the GPS satellites are, and surprisingly much on the time of day (it is much better in the morning). My guess is that during the day the sun excites the ionosphere which already before that is one of the largest contributors to the GPS measurement error.