Week 5

Levels can be used to create contour lines for an area, by obtaining levels using specific points, this is called indirect contouring. One method of indirect contouring is using method of squares (also known as grid contouring). This involves setting up a series of squares, with specific centres and levelling all of the grids, allowing for interpolation of contour lines between the grids. For this activity, there is a 5x4 grid at 10m centres on a hill within the university grounds and a TBM located on a bridge in the adjacent woodland with a height of 69.214m AOD. Obtain the reduced level for all grid points, relative to the temporary bench mark and calculate the overall error of the survey.

Process

1)   Start with a backsight on the temporary bench mark on the bridge and fly level across the field to the hill.

2)   Once at the hill, take a series of intermediate readings along line 1.

3)  After the intermediate readings, fly level round the hill until you have picked up all of the grid lines.

4)  Once you have picked up all points on the hill, go back to point A1 and take another reading with the stave positioned there, this will allow an additional check once the survey is complete

5)  Fly level back to the original bridge to close the survey

6)  Add up all backsights and foresights, minusing one from the other to obtain the overall error. This should be less than 1mm/change point.

Helpful Tips

·   Draw the points in the comments section and cross them off as you achieve them.

·   Level to the top off the hill and get as many points as you can see, then on the way back down collect any points you may have missed using the sketch above. 

·   Plan setup locations before moving the instrument to ensure maximum visibility.

·   It may be helpful to setup in line with each row and obtain a series of intermediate points for that line.

·   Try and create a series of points you use on the way to and from the hill, helping create more control in the survey

Practical Video Guide