Virtual Surveyor announced new functionality in the 10.2 release of its smart drone surveying package to project GPS-based drone imagery and lidar data directly to the local coordinate system without going through a third-party package. This greatly enhances the convenience of mining or earth-moving surveying projects where not being able to work in local systems is a major bottleneck.
The primary issue of working with national coordinate systems for surveying, mining, and earth-moving projects is accuracy, not convenience, explains Virtual Surveyor CEO Tom Op ‘t Eyndt: “When working in a global or national coordinate system, distances measured on the grid do not always match true ground distances due to projection scale effects. A distance that is exactly one meter on the ground will still be one meter at higher elevations, but when that same distance is derived from projected coordinates, small distortions can occur depending on location and projection.”
For general mapping or geographic analysis, these differences are negligible. However, in surveying, mining, and earth-moving projects, even small discrepancies matter. When distances are slightly underestimated, calculated volumes are underestimated as well. That directly affects operational planning, such as the number of truckloads required, and ultimately leads to underestimated costs. In competitive projects, those small errors can translate into real financial losses, explains Op ‘t Eyndt.
How it works
Essentially, the technique to define a local coordinate system works for any project site in the world with at least control points measured with GPS/GNSS (Geodetic reference) and a total station (ground reference). The user inputs these points, after which the TerrainCreator app will calculate all coordinate system parameters in the background. The resulting local coordinate system is defined using the WKT standard, ensuring that all necessary information is available for accurate reprojection to other coordinate systems when needed.
The bounding box around the GNSS measurements determines the validity area for contraction or mining construction sites. These coordinate system are only valid for small areas of typically a few square kilometers, often smaller. Figure 1 contains an illustration of such a point mapping. More info is available here.
How coordinate reprojections fit in a larger photogrammetric workflow
The drone photos loaded in Virtual Surveyor’s TerrainCreator app contain positions in Latitude, Longitude and Ellipsoidal height measured to the WGS84 ellipsoid. Within the TerrainCreator app, these coordinates are reprojected after data capture to the user-defined local coordinate system using GDAL, which is built into the application. Once the data is in the correct coordinate system, photogrammetric processing takes place, resulting in a digital surface model (DSM) and orthophoto that are fully positioned with the local project coordinates. These results are then transferred directly into Virtual Surveyor for survey analysis and volume calculations.
In a 3rd party workflow this would not be different: here, a user would produce the DSM and orthophoto in the local coordinate system in the 3rd party app and load then import the results into the VirtualSurveyor app for surveying. The key difference is efficiency, concludes Op ‘t Eyndt: “That approach requires users to master and switch between multiple software packages, and often to license both. By integrating this workflow into a single environment, Virtual Surveyor allows users to complete the entire process more efficiently, in one package and at one cost.”
