A quick overview on how it works
The method primarily revolves around Photogrammetry, a multi-disciplinary approach to image interpretation, the output is an orthomosaic (or orthophoto) which can be acted upon by the software to provide the required answers.
The drone provide the platform for the initial input. The drone using GPS to plot its position/heading and the camera providing and image which can be interpreted at the point level. A particular flight plan may generate hundreds of these images and this allows the software to detect very small differences in each images and stitch the entire shoot into one to generate a 2D or 3D model of the scene.
From this digital scene a skilled operator can then extract the required information, be it volume, fill or cut.
Relative V Absolute Accuracy
The need for improved (sub centimeter) accuracy will be determined by the individual project and associated values. All sampling methods have some variation and this variation can be reduced by using additional Geometric measuring systems to provide a higher degree of accuracy. The value of the product in question and the nature of the location will determine if the added expense of generating ground control points and or checkpoints is worth the additional costs.
Improvements in relative accuracy (as in the accurate dimensions of the project we are measuring) can be achieved with the addition of mapping stations (Base & Rover) which can help lock down distances and elevations around the project area and or the use of checkpoints (real world measurements of items in the image) which can then be used to lock the scale in place.
Some projects may also call for improved absolute accuracy (identifying the location of the project and its dimensions in relation to its location on the planet) and this can be achieved with a mapping station and the additional of specialized radio broadcasts which are received by the base station and rover.
If you have a particular project you would like to discuss in more detail, please contact us and we will be more than happy to assist.