How to Survey a Field for Landforming Design
When a survey is performed, it creates a survey file for the field that contains a collection of data points. Each point represents a specific latitude and longitude or Easting and Northing position within the field for which an elevation value is stored.
The data collected can be valuable to create informational maps. Any maps created from this data is only as good as the quality of the data that creates it. In order to create quality maps from your field survey data, be sure to perform your field survey to the highest quality. As a start, please observe the following guidelines as a minimum for performing a field survey.
- Use a RTK GPS receiver with a local base station within 1km (0.6 miles) of all parts of the field for the highest accuracy and quality survey data (eg +-10mm vertical accuracy 70% of the time). Using an RTK correction from networks or satellite services will generally lead to inaccurate elevation maps (eg +-100mm) which leads to increased earthworks and earthworks imbalances. See here for more details.
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Physically mark a Master Benchmark on the ground and record its GPS position with your screen. This becomes a fixed reference point that the earthmoving blade is placed on to zero out any horizontal and vertical coordinate differences. A concrete mark is good. At the very least, mark the sides of the survey vehicle inline with the GPS antenna using two pegs that will remain in place until the earthmoving machine does the work.
- Make
the first pass on the exterior field boundary, when collecting survey
data, to ensure sufficient data around the perimeter of the field for
the design surface to extend to. OptiSurface Designer will extrapolate
(extend) the design surface a little outside the defined survey
boundary. This extrapolation distance could be 1m (3ft) in some places
around the boundary and further in other places eg. 10m or 30ft,
depending where the calculation grid falls.
- Conduct a thorough survey by driving up and down the field on approximately the following swath spacing:
• Fields with significant elevation changes and slopes — swath spacing of 7.5—15 m (25—50 ft.) is recommended.
• Flatter fields — a swath spacing of 15 m (50 ft.) is recommended.
• Flat to precision leveled ground — a swath spacing of 15—30 m (50—100 ft.) Do not exceed 50 m (100 ft.) swath spacing for surveying purposes.
- The recording distance between the survey points as you drive along the tracks should be approximately 1 second or 5 m (15 ft). There's no need to stop at every point, just continue driving. At about 15 kph (~10 mph) recording every second you get around 5 m spacing. If it is a lot smaller than (eg 1 m) then the number of survey points can become large and get slower for the software to handle and process for fields larger than 100ha (250ac).
- Ensure
that the entire field has been covered. Do not skip parts of the field
because they are inaccessible due to wet or muddy conditions; you are in
a hurry; you think you do not have time to finish properly. This has a
negative impact on the quality of your maps generated from your
collected data. It is important to cover the entire field.
- It is also a good idea to survey the bottom of existing ditches and large depressions so that the terrain shape is correctly recreated in the design software. Utilizing parallel tracking with straight track can cause the user to miss areas of interest for surveying, for example the bottom of a main ditch which can have an obvious width and depth. Driving along the shoulder (top off batter) of large ditches can also be worthwhile to better define the shape of the topography.
