A 371Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE
Distance dependent intersections are complimentary tools for the retracement surveyor. When contemplating intersection methods one should consider whether or not the values were actually measured in the field. Such might be the case with a radius point for example.
Last month we covered direction/ direction intersection which is a well suited application for retracing linear measurements. Curve data is a derivative of the intersections of the tangent lines. Holding the bearing/bearing intersection of the monumented lines recreates a p.i. that places you very close to the position of the transit man during the original survey. The observed deflection between these intersected tangents IS THE REAL DELTA! Both ends of the curve are either found or replaced as originally set on these intersected lines. The retracement function is fulfilled through a recapitulation of physical evidence presented on the ground.
A strong application of distance/distance intersection is found among swing ties or cross ties physically measured from reference marks to monuments or from property corners to building corners. These are direct measurements from known points and a great demonstration of rope stretching to the Courts.
I don’t think much in terms of direction/ distance intersections in retracement work. There is a platted mirage at the "end lots" of a block that can appear like the intersection of a directional right-of-way line and an end lot distance. Exhaust without doubt every shred of physical evidence before using a direction/distance intersection. If itching and rash persist induce vomiting and call your physician immediately.
A Few Thoughts On Constructing Radius Points
Distance/distance intersections often yield inconsistency among the ground evidence affixing curvilinear boundaries and create tension in the opinions of the paper minded surveyor. Considering the legacy knowledge that curves were originally placed on the ground by measuring the deflection angle, the tangent length, and the chord distance, evidentiary weight of a calculated radius point is severely disjointed from those implicit facts of conventional measurement. The original surveyor measured along the curve naturally shedding imprecision and error linearly through the curve. Neither his path nor measurements extended to a radius point. A computed radius offers zero contradictory evidence to upset the original work measured ALONG the line. The retracement surveyor will find more comfort in working lineally through the curve holding bona fide evidence found on the ground.
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This Month’s Program
Program L: Intersections includes routines for Direction/Direction, Direction/ Distance, and Distance/Distance. The program operates by assuming a base line from the first point to the second point. Direction/Distance and Distance/Distance naturally have 2 solutions. The preferential solution may be defined as being left or right of the line facing the second point. This month we will focus on Direction/Distance and Distance/Distance examples.
See the PDF
Jason Foose is the County Surveyor of Mohave County Arizona. He originally hails from The Connecticut Western Reserve Township 3, Range XIV West of Ellicott’s Line Surveyed in 1785 but now resides in Township 21 North, Range 17 West of the Gila & Salt River Base Line and Meridian.
A 371Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE