Words by Guy Kantorowich, British Gypsum
Stockpile surveys are the ‘bread and butter’ of many surveyors, with regular surveys required from an accounting standpoint. Depending on the material being surveyed, how accurate the survey needs to be, and how the stockpile has been constructed the survey can be quite laborious and time consuming. Also if the site, as in this case study, is an active quarry operation with moving machinery and plant the survey can pose certain health and safety risks to the surveyor, who has to negotiate climbing over and around the stockpile whilst also avoid collisions with any moving plant. Since the development of rover GPS units this was the preferred method for conducting such a survey. The surveyor can accurately map the stockpile with one instrument with little else required. Processing the survey is also a relatively simple task especially when you have the base of the stockpile surveyed to GPS as well. The drawback is that the surveyor has to physically take every measurement required to map the stockpile which, as previously mentioned, can be very time consuming.
GeoSLAM’s ZEB Horizon is a portable hand held laser scanner which offers a solution to some of the problems with the traditional GPS method. The scanner boasts impressive figures with 300,000 points per second collected, 100m range with up to 1cm accuracy all surveyed in real time whilst on the move. The ZEB Horizon produces point clouds in various export formats with the function of reducing the number of points in the survey by a percentage to reduce the file size and processing times. The unit relies on SLAM (Simultaneous localization and mapping) technology which is simultaneous localization and mapping is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of an agent’s location within it.
To assess the capabilities of the scanner compared to the GPS we conducted the monthly quarry stock survey with both instruments on the same morning.
Scanning on site with British Gypsum
Geo-referencing Point cloud
Depending on the conditions of the stockpile a base survey of the stockpile area may be required. This is generally done when there is an uneven surface or obstructions beneath the stockpile which need to be taken into account when calculating the volume of the stock. For this case study using a GPS base model was important so geo-referencing the point cloud was required. We used three spheres placed around the stockpile, which were surveyed by placing the GPS receiver on top of the sphere and then reducing the level to the center of the sphere. In post processing the coordinates were assigned to the spheres picked out from the point cloud to then accurately geo-reference the survey.
GPS Rover vs. ZEB Horizon
The ZEB Horizon also has the potential to be vehicle or UAV mounted. This would further reduce the risk to the surveyor. Internal stockpiles are surveyed with even greater ease when compared to a one-man total station with no more multiple set-ups and complex resections.
Overall I believe that this technology has the capabilities to completely revolutionize the surveying of stockpiles. As a surveyor who has spent many years clambering over stockpiles getting increasingly frustrated at the complex, uneven, messy nature of them the ZEB Horizon is a breath of fresh air.