RTK Under Canopy Versus Total-Station Traverse
You are retracing a 12-acre wooded parcel in the Adirondack foothills. Two NGS control points 1,850 ft apart are available, but the line between them crosses a dense hemlock stand. Your RTK base is set on one point; the rover obtains fixed solutions only in a 60-ft clearing, with horizontal repeatability of 0.04-0.09 ft and vertical repeatability of 0.12-0.20 ft. Under canopy, fixes drop to float, PDOP rises from 2.1 to 5.8, and the radio link fails. The boundary corners are marked by old cedar stakes and blazes. A total-station traverse from the two control points closes with 18 arc-second angular misclosure and 0.06 ft linear misclosure over 3,100 ft. The client needs a boundary map at 1 in = 100 ft and a 2-ft contour overlay. You have one day and one two-person crew.
1. Should the RTK-derived positions be used to set or hold the boundary corners? Justify your decision using the observed data.
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No. The RTK results are not reliable enough for boundary positions in this setting. A fixed solution obtained only in a clearing, with horizontal repeatability of 0.04-0.09 ft, does not demonstrate the independent accuracy needed under canopy, and the float solutions are weaker still. PDOP 5.8 and radio dropout are warning signs, not merely inconveniences. Boundary location is primarily a relative problem: the recovered cedar stakes and blazes must be tied to each other and to the parcel's occupation with consistent internal geometry. A total-station traverse closing 0.06 ft over 3,100 ft is about 1:51,700, far better suited to holding corners and checking the RTK. Use RTK for open-sky control checks or preliminary reconnaissance, not for final boundary positions. If RTK is used at all, require repeated independent occupations, fixed-only solutions, and a total-station check on at least two boundary lines. Record the rejected solutions and the reason.
2. What field procedure and records would you require to support the boundary map and the 2-ft contours?
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Establish the total-station traverse from the two NGS points, closing on both, and hold the boundary corners by traverse. Measure distances both forward and backward where practical, record temperature and pressure, and check prism constant and instrument height at each setup. Tie every recovered cedar stake and blaze by offset and bearing, and note its condition. For the contours, do not interpolate from boundary traverse shots alone. Take a grid or breakline survey at a spacing suited to 2-ft contours, including ditches, banks, and the steep hemlock edge; check vertical closure at the control points. Keep raw field notes, station descriptions, and a traverse sketch. Compute the traverse independently before drafting. On the map, state the horizontal and vertical datums, the traverse closure, the source of the contours, and that the boundary is based on the recovered monuments. This record lets a reviewer see why the RTK points were not used and how the map was controlled.