In-depth mining analysis is required for accurate planning, mapping, and safe extraction of minerals and ore assets. Geographic Calculator and Global Mapper Pro can help mine site managers model active and potential mines to optimize asset extraction.
Combining the wealth of GIS tools found in Global Mapper Pro with the geodetic accuracy of Geographic Calculator, asset positioning, terrain analysis, and data visualization are streamlined. From converting coordinates, referencing local grid systems, visualizing terrain, and calculating pit and pile volumes, Blue Marble offers all the tools needed to complete a thorough mine site analysis.
Working in a Custom Mine Grid
Mine and engineering projects often begin with local surveying. While some mine surveys use conventional coordinate reference systems, many employ custom grids based on measured distances from a local origin point. While custom grids provide a high level of accuracy for a local area, the sharing and mapping of a mine area often requires these custom grid coordinates to be transformed into a known system. Geographic Calculator’s Best Fit job makes it easy to create a transformation between a local grid and a known system.
Like many jobs in Geographic Calculator, the known reference system in a Best Fit job can be selected from the software’s extensive datasource. The input data required to derive a relationship between a custom grid and an established system are a set of control points surveyed in both the custom and known reference systems. The control points surveyed in a known system can even be collected using the accurate GPS data collection methods available in Global Mapper Mobile Pro, a powerful mobile mapping application available in the iOS App and Google Play stores.
Using the Best Fit job in Geographic Calculator, the control points are used to derive a polynomial transformation between the custom and known systems. After deriving the required transformation parameters, an error plot can be viewed to show the fit of the equation, and control points with larger or disagreeing error values can be removed to modify the fitted system. Once created, the fitted system can be saved in the Geographic Calculator datasource and used to transform any other data to or from the custom grid reference.
Visualizing and analyzing the topography of proposed or existing mines is an important aspect of the GIS work undertaken in the mining industry. Global Mapper Pro’s terrain creation, visualization, and analysis tools allow data managers to explore and measure terrain in 2D, cross-sectional, and dynamic 3D views.
Terrain data for a project area can be downloaded from an available online source, created from a lidar point cloud, or generated from a set of overlapping, drone-collected images in the Global Mapper Pro’s Pixels to Points tool. Unreferenced or misplaced terrain can then be rectified based on surveyed control points to ensure the accuracy of display and analysis. Once a terrain model is loaded into Global Mapper, the topography is shaded to reflect variation in elevation or slope characteristics. This terrain visualization can be further customized through the use of shaders. Imagery, freely available or collected by aircraft or drone, can be draped over a terrain surface to provide additional context and detail to the 3D visualization of the project area.
Deriving Vector Data
Deriving vector data from a digital elevation model is made easy in Global Mapper Pro, which includes tools for contour creation, breakline extraction, and multiple options for data export.
Contour lines are easily created in Global Mapper with a dedicated Contour Creation tool. Accessed from the Analysis toolbar or menu, this tool generates elevation isolines based on the loaded terrain data. With options to find local peaks and depressions, contour creation may be a good first step when digitally exploring a new-to-you project site, or communicating variation in terrain via a map.
Identifying local peaks and depressions in an open mine area creates points at any noticeable pits and piles throughout the job site. These features will be clearly visible on the map as vector points, and can be edited and renamed to better describe the identified features.
Using a single contour created in a set, or choosing to generate a single contour iso-height area at a specified elevation, a feature tracing the approximate base of a pile or the edge of a pit can be identified and used to calculate volume. Creating iso-height areas in the contour creation tool generates polygon features at the defined elevation. If using an existing contour line to identify the pile or pit in the terrain, the feature can be selected and converted to an area using Global Mapper’s digitizer tool.
With an area bounding the pile defined, the Pile Volume option within the Digitizer toolset is used to compute a pile volume or pit capacity for the terrain within the bounding polygon. By sampling the elevation along the polygon boundary, a representation of the original surface is created in the background and subtracted from the current surface to derive the volume.
An alternative method for identifying piles, pits, and other changes in terrain is the creation of breaklines in Global Mapper Pro. Instead of representing a single elevation along the line, like a contour, breaklines delineate edges in the terrain where there is a significant change in elevation or slope. Again, accessed from the Analysis toolbar or menu, breakline extraction in Global Mapper Pro offers three methods for automatic breakline extraction.
With options based on slope and curvature, the identification of edges in a mining area terrain model describe flat areas and can effectively reflect the edges of piles and pits, where a notable change in slope and curvature occurs.
Similar to pile and pit volume calculation based on contours, a breakline outlining a stockpile or mine pit can be converted to a polygon with the digitizer and used in a volume calculation. This approach is particularly useful when the original terrain is inclined so the volume calculation is not based on a specific elevation. Unlike contours, breaklines are not isolines so they can more accurately bound a feature.
Another form of vector data that can be derived from a terrain model is a 3D mesh. This can be accomplished with the Create 3D Model/Mesh option in Global Mapper, or by simply exporting the digital elevation model to a mesh format, such as DWG TIN or Land XML. These formats are often used by engineers and are common throughout the mining industry.
Displaying a subsurface model in conjunction with a surface terrain layer in Global Mapper allows for visual and calculated analysis of the offset within the area. Multiple gridded terrain layers can be viewed in Global Mapper’s Path Profile and 3D views. From an oblique or cross-sectional perspective of the 3D layers, the depth of the subsurface layer can be seen and measured.
For a more comprehensive quantitative analysis, a difference model can be created to visualize the depth of the subsurface layer. Using the Combine/Compare Terrain Layers tool in Global Mapper, a subtraction calculation is applied to the surface terrain and subsurface layers, resulting in a gridded layer modeling the elevation difference between the two source grids. A custom shader can be applied to the difference grid, and this layer can be used to apply depth or difference values as attributes to vector features in the workspace.
Combining the powerful capabilities of the Blue Marble programs for GIS and geodesy results in a complete mine site analysis with custom grid transformations, terrain analysis, feature creation, and volume calculation. Any data displayed or loaded in Global Mapper can be exported for sharing and reprojected to local grid coordinates with Geographic Calculator if necessary.