Setting out techniques
These techniques involve an iterative process. A detail pole is held in approximately the correct position. A reading is then taken and the deviation from the required distance is calculated, the detail pole is then moved this amount and another reading taken. This process is repeated until the required accuracy is achieved. Most engineers will recognise this technique as stakeout and will use it after calculating bearing and distance to the point to be set out (target point) from the instrument (station point). The following techniques are variations on this theme. For accurate work a mini-prism (view picture) should be used. This is a prism, which is approximately 100mm high and has a plumbing bubble, accuracy @ 3mm.Setting out easting and northing to give grid lines
Setting out curves by distance from the centre point
Setting out non-square grids by chainage and offsets
The above techniques are more suitable for site conditions and the presence of obstructions than calculating and then setting out discrete points as with these methods only one direction is fixed. Calculation time is also significantly reduced. The next generation of total stations will have much greater memories and the facility to run user-generated programs (see example). A Psion II can also be attached directly to an EDM and run software. This would eliminate any booking errors.
Setting out easting and northing to give grid lines
Using a total station or programmable calculator (programme coordinates from bearing and distance) obtain the coordinates of the prism position. Move the prism until the required easting or northing is achieved. Repeat this for the other 3 points. This method can be used for setting out kickers.
top
Setting out curves by distance from the centre point
Obtain the coordinates of the prism position, then using a programme (bearing and distance from coordinates) calculate the distance from the centre of the curve to the prism position. Move the prism until the distance from centre point equals the radius.
top
Setting out non-square grids by chainage and offsets
Obtain the coordinates of the prism position, then using a programme (chainage and offset from coordinates) calculate the chainage and offset from the given line. Move the prism until the offset is zero (or the required value). Repeat to obtain the required chainage. This technique can be employed for setting out kickers on non-square grids or a drainage run which is not parallel to grid north.
top