Volumetric Surveying

in Volume

What is Volumetrics?
The measurement of the inside of a three-dimensional area is known as its volume. This is easily illustrated by looking at a coffee mug. By measuring the diameter of the mug and calculating its height, you can determine exactly how much liquid will fill it to the brim. This same method can be used to determine the volume of virtually any three-dimensional object. The complexity of a shape in nature, however, is one reason why it is necessary to hire a surveyor to do the necessary and highly intricate calculations for any land-type application.

Who Needs Volumetrics?
One of the most common uses of volumetrics is in the construction and landscaping industries. It is sometimes referred to as "cut and fill," in that material is cut from one location and moved in volume to fill another. First it must be determined how much matter-dirt, rocks, and so on-is to be extracted. Then a suitable place must be found that will accommodate the same volume of material, if not more. The location receiving the cut material must also have its contour (slope) and other factors included in the analysis.

Not only is it important to determine that the receiving zone is adequately sized to accept the transported material, but one must ensure that it will stay put. Municipal water utilities use volumetrics to measure the amount of water in a reservoir and how close it is to capacity. Mining companies worry about what they are digging up and where the excess-often called tailings-can be safely stored. Golf course designers use cut-and-fill measurements to scoop out areas for sand traps and use the removed dirt to build up ridges and smooth out fairways.

Using a Surveyor to Determine Volumetrics
The trained surveyor has a number of tools at his or her command. While it is possible to determine the volume of an area by using ground-based surveying alone, the easiest method will add in airborne surveying and the process known as photogrammetry (aerial photography). Using these two techniques together will help achieve the most accurate results possible. On the ground-based side, a surveyor will use a total station (a highly sophisticated electronic version of the old surveyor's transit) tied to a GPS network, plus a laser rangefinder. This latter device uses laser light to determine the exact distance from the base station to a particular point.

The resulting measurements are stored in a software database. Aboard the aircraft is an aerial camera that photographs the target area with fairly high resolution. Many airborne surveyors now employ digital cameras that capture imagery in a format that easily merges with the data collected on the ground to create what is called a three-dimensional digital terrain model (DTM). However, even older, film-based aerial cameras are quite sufficient to achieve similar results. However, the photos must go through a secondary digitization process in order to prove useful in building the DTM.

Calculations
To determine the volume of a particular area, first the boundaries are pinpointed using standard surveying methodology. These are tied to specific points in space through the use of GPS, which is accurate to within a few centimeters or better. These boundaries are digitized and then imported to the airplane's navigation system, at which point aerial photographs are taken of the entire area.

Using some very sophisticated software, a DTM is generated through the manipulation of data from both air and ground sources. By combining these methods to determine the volumetrics of a particular 3D area, one can usually achieve accuracy within the three-percent range. It is the rare job indeed that would require anything more accurate.

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Peter Brittain has 1 articles online

Land Surveys Pty Ltd are licensed surveyors and provide a complete array of surveying services in Perth & Karratha, Western Australia.

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Volumetric Surveying

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This article was published on 2010/03/31