TPC can compute the position of a lost corner using the Single Proportionate Measurement method as described in the Manual of Surveying Instructions 2009, page 168, section 7-16. This method requires two existing corners, record data from the existing corners to the lost corner and retracement data from the existing corners to the lost corner. This method uses grid bearings and distances with the option to compute the latitudinal offset.
TPC computes the inversed retracment and record distances between the two existing corners and applies the ratio (retrace distance / record distance) to the record distances. It then uses the inversed retracement bearing/azimuth to compute the position of the lost corner.
TPC uses the words Retrace and Measured interchangeably when referring to lost corner computations. These are the measurements you make fromt he existing (found) corners, retracing the footsteps of the original survey. These measurements result in a temporary location for the lost corner, which TPC refers to as the Temporary Corner. And because the temporary corner can be set in the field, TPC provides offset distance and direction data to set the lost corner from the temporary corner.
TPC does NOT use typical batch computations involving formatted text files. Such batch methods are often cumbersome to learn and use.
Instead, TPC expects you to create Retrace and Record traverses for each lost corner. The traverses are a permanent part of the survey and can be re-used as needed to recompute the lost corners. In addition, the traverses provide drawings and printouts of the data you used to compute the lost corners.
We recommand that you open the Single Proportion Dialog from the Traverse View using traverse layouts like the printout below. The words 'Retrace' in the first traverse name and 'Record' in the second traverse name identify which data in the Single Proportion dialog is represented by each.
Using this method, each traverse can be used to quickly populate the Single Proportion dialog, eliminating the need to enter any data manually.
[[ Traverse View - Single Proportion - Retrace (True Bearing, Geo
Dist, Chains) ]]
Geo Dist (at project elevation 0.00 PLSS)
True Bearing (mean course convergence PLSS)
Point Type True Bearing Geo Dist Latitude
Longitude
a
40°13'54.886"N 138°14'12.812"W
b S83°09'20"W
39.96 40°13'51.780"N 138°14'46.575"W
c S80°54'19"W
41.06 40°13'47.547"N 138°15'21.076"W
[[ Traverse View - Single Proportion - Record (True Bearing, Geo
Dist, Chains) ]]
Geo Dist (at project elevation 0.00 PLSS)
True Bearing (mean course convergence PLSS)
Point Type True Bearing Geo Dist
Latitude Longitude
f
40°13'47.835"N 138°14'11.201"W
e S82°19'20"W
39.96 40°13'44.353"N 138°14'44.901"W
d S82°19'25"W
40.16 40°13'40.854"N 138°15'18.769"W
Retrace Data/b>
Highlight point b in the first traverse and choose COGO, Single Proportion. TPC looks for the words 'Retrace', 'Temporary' or 'Measured' in the traverse name. Point b then becomes the Temporary Corner while points a and c become the existing corners, using ther orientation with b to deteremine which existing corner they represent in the dialog.
Record Data
HHighlight point e in the second traverse and choose COGO, Single Proportion. TPC looks for the word 'Recrord' in the traverse name. Point e then becomes the Lost Corner in the dialog. Points f and d are inversed to generate the record data, using their orientation to e to deteremine which record data they represent.
TPC displays all the data used to compute the lost corner in the Single Proportion Report.
The latitudinal offset (if requested) is computed using the following equation from Elgin-Knowels-Sinne as set out in POB tech tips. If you have not selected a coordinate reference system for this survey, the offset will not be computed.
offset = (0.6668) (LW) (LE) (Tan Latitude)
where LW = distance from the lost corner to the west existing corner and LE = distance from the lost corner to the east existing corner.
The latitude is computed based on the coordinate reference system selected for the survey and the coordinates of the computed position of the lost corner before it is offset.
Single Proportion Dialog
Cadastral Survey
Professional