A precise level run was undertaken to constrain the network in the vertical component and to subsequently determine orthometric and ellipsoidal heights for each station after the least squares adjustment in Columbus. Observations were carried out as per specifications for differential levelling in SP1 to achieve a class LA levelling run. Several “braces” were observed in the network between SS23 and SS22, SS12 and SS18 (including each station in between) and SS07 to SS21 so that more redundant observations were included in the least squares adjustment. A list of the equipment used in the precise levelling run is below.
- Zeiss Ni1 Precise Level - Serial Number 81392
- 1 Tripod
- 2 Invar Staves – Serial Numbers 36446011, 36446012
- 2 Change Plates
- 2 Range Poles
- 50m Measuring tape
The methodology adopted to carry out the precise levelling run is outlined in the following few points.
Before undertaking the precise level run, a two-peg test was undertaken to determine the collimation error of the instrument.
Following from here, staff A was set up on SS00 and staff B on a change plate (less than 80m away from SS00 as the line of sight must be no longer than 40m). The instrument was then set up half way between these two points.
- The observation procedure of BS:L, BS:R, FS:L and FS:R was then carried out.
- An observation error was then calculated by subtracting the foresight value on the from the backsight value on the left and right scales of the staves. If this difference was below 0.00020m than the level run was continued otherwise the set up was observed again.
- This process was carried out until the each point in the campus network had been levelled.
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