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The 2021 MINIMUM STANDARD DETAIL REQUIREMENTS FOR ALTA/NSPS LAND TITLE SURVEYS (effective February 23, 2011) as adopted by American Land Title Association and National Society of Professional Surveyors defines how to test for Relative Positional Precision (RPP).
Previous standards presented the RPP definition of 0.07’ or 0.2cm and 50 ppm and discussed the use of an appropriate minimally constrained least squares solution using a 95% confidence interval, but did not explain the combination or sequence of points to be used in the test.
The 2021 Minimum Standard finally describes a main test and an alternate test in section 3e1 as follows.
Test #1 Main Test
“Relative Positional Precision” means the length of the semi-major axis, expressed in meters or feet, of the error ellipse representing the uncertainty in the position of the monument or witness marking any boundary corner of the surveyed property relative to the position of the monument or witness marking an immediately adjacent boundary corner of the surveyed property resulting from random errors in the measurements made in determining those positions at the 95 percent confidence level. Relative Positional Precision can be estimated by the results of a correctly weighted least squares adjustment of the survey.
Test #2 Alternate Test
Alternatively, Relative Positional Precision can be estimated by the standard deviation of the distance between the monument or witness marking any boundary corner of the surveyed property and the monument or witness marking an immediately adjacent boundary corner of the surveyed property (called local accuracy) that can be computed using the full covariance matrix of the coordinate inverse between any given pair of points, understanding that Relative Positional Precision is based on the 95 percent confidence level, or approximately 2 standard deviations.
Defining the Sequence
The 2021 Minimum Standard includes the language monument or witness marking an immediately adjacent boundary corner of the surveyed property for both tests.
For Test #1, the adjusted survey points for this sequence are tested, while for Test #2, the adjusted distances of this sequence are tested.
TPC defines this sequence in a traverse, allowing you to select one or more traverses to apply these tests to. Typically, this will be the boundary traverse for the property being surveyed.
Related Topics
ALTA/NSPS Land Title Surveys
Editions
Professional
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