Volumetric Surveys

At  Grand Lake Surveying we have the capabilities to carry out surveys to  determine the volume of material stockpiles, amount of material removed  from excavations and quarries, change detection, and several other  applications involved with volumetric calculations.

There are  several methods to determine such values which can be broken down into  two main categories: ground/terrestrial based data collection and aerial  data collection.

Ground Based Collection

There  are several methods behind ground based data collection, such as survey  grade GNSS (GPS) data, a terrestrial based LiDAR (Light Detection and  Ranging) scan to a point cloud, and a total station with ground  measurements.

Aerial Data Collection

Aerial  data can be collected with two methods: LiDAR (Light Detection and  Ranging) and/or photogrammetrically. Both methods can be collected from a  manned or unmanned (UAS or Unmanned Aerial System) flight platform.

Photogrammetry

Photogrammetry  is the science of making measurements from photographs, specifically  for recovering the precise positions of surface points. Conventionally,  the method used to extract this information was planimetric collection  and 3D break lines from stereo models. Today, new algorithms for dense  image matching and pixel recognition brought Structure from Motion (SFM)  into the main stream. SFM utilizes the collection of images from  different perspectives to generate a point cloud based from pixels. This  is done by matching key points between photos and triangulating the  pixels from the know attitude of the camera, through the systems IMU  (inertial measurement unit) and GNSS receiver, and generating an  extremely dense point cloud (dependent on altitude, focal length, and  exposure rate of the camera).

LiDAR

LiDAR  or Light Detection and Ranging is the use of lasers and extremely  precise timing to generate a point cloud (a population of 3D  coordinates). The instrument has known coordinates, from either the  attitude of the aircraft/vehicle or set up over a known point (like a  how typical total station is used). The laser (which is in the  non-visible spectrum of light) pulses at a set rate (Hz/ KHz or even  MHz). As soon as the pulse is emitted an internal timing mechanism  calculates the time of flight. The distance can be calculated using the  time of flight and the speed of light (1/2*Time of flight/speed of  light). The angle of the laser is known a posteriori through sweep  angles and scan patterns. Repetitions of these calculations build a  point cloud.

Volumes

Through  these methods a 3D point cloud/surface can be created, allowing for  extremely accurate volume calculations. With surface to surface  comparison, one of the most accurate methods, a model created  pre-operation is compared to a post construction model. This allows for  volume calculations or change detection. “Toe polygons” can also be used  to create a new planar surface for calculations, which acts as a  “pseudo baseline”. As technology progresses these measurements will be  modeled and tabulated at an even greater density and speed.