Before starting your work, it is key that you assess whether or not you need to clean your elevation terrain. Stockpile calculation and cut/fill maps are instances where the answer is clearly YES, but if your final deliverable is a topographic survey, then the answer is definitely NO.
The first step to helping you decide when to clean the terrain is to determine what deliverable you need to produce. If that final product requires initial elevation terrain cleaning, Virtual Surveyor provides you with a complete toolset. Depending on the use case and on the type of surveyed area, you use the tools that are relevant for removing surface items. Virtual Surveyor does not work with automatic DTM extraction.
| Deliverable | Clean Terrain? |
|---|---|
| Stockpile Volume |  |
| Cut/Fill Map |  |
| Digital Elevation Model (DEM) |  |
| Contour Map |  |
| Q-Points Surface |  |
| Wooded Area Surface |  |
| Surface (Mine Survey) |  |
| Lines Survey |  |
Cleaning Tools and When to Use Them
Stockpile Volume
On mining or crushing sites, crusher arms or conveyors may feed stockpiles. Stockpile volume calculation should not include machines and equipment items. Before creating the reference surface and calculating a stockpile volume, it is necessary to remove the overhanging conveyor. The easiest way to remove it is to use the Remove Object tool to erase the conveyor in one click. For more complicated surface items that the Remove Object tool cannot detect, use the Replace Terrain tool, which allows you to outline the entire object for removal.
Cut/Fill Map
Cut/fill maps are used to manage earthwork progress. Those kinds of maps are generated between two terrain states or between a terrain state and a design surface. In both cases, machines and other non-relevant objects must be removed to deliver an accurate cut/fill calculation. The easiest way to do it is to use the Remove Object tool to erase those items in one click. Otherwise, use the Replace Terrain tool to outline the objects for removal.
Digital Elevation Model (DEM)
Drone photogrammetry often creates odd noise on water surfaces and these areas may need to be cleaned on a case-by-case basis for GIS application. The water noise is not easily apparent when looking at the orthomosaic or Image Terrain, you need to turn on a Terrain Lens filter or untick the Image Terrain in the Project View to easily spot the noise. In this example, you can see the noise with the Image Terrain turned off.
To clean the water's surface, use the Boundary tool to create a boundary around the water, Triangulate Within the boundary, and click Modify Terrain.
Contour Map
Contour maps are commonly used by surveyors to illustrate terrain elevation. Contours maps need to resemble the terrain and should not include surface items (tractors, machines, equipment, etc). Cleaning these items from the terrain is not necessary in this case. When creating a surface with contours, the first step is to create a survey of points and lines. You avoid placing points and lines on any surface items so that the surface items are not included in the created contour map. The contour lens found in the Analysis tab is only used for examining the elevation terrain. Please keep in mind that you can only export contour lines that are created from your Triangulated Irregular Network (TIN) in Virtual Surveyor.
Surface with Q-Points.
This workflow is usually implemented in a large open area like an earthwork construction or mining site. To turn your elevation terrain into a lightweight TIN, you can generate an intelligent points grid and triangulate it. The Q-Points algorithm places points on the terrain where the elevation exceeds the desired Elasticity. Generally, it drops more points on large slopes or hills than it will on any flat surface depending on the elasticity settings you give the tool to work with. Vehicles, buildings, and trees will often be covered with points due to the effect of the elasticity settings of Q-Points that respond to objects on the terrain. If the goal of the survey is to measure ground elevation, it is better to delete points that land on top of your surface items using the Select Area, or Erase tools.
Surface with Low-pass Points
This workflow is usually implemented in a large wooded area with an open canopy. To generate a lightweight TIN of the ground elevation, you need to survey around the vegetation. In this case, it is not necessary to clean the elevation terrain. Instead of cleaning the terrain, use the Low-Pass Points tool and triangulate the resulting points grid to generate the surface.
Mine Surveying
You can quickly create a survey map of a mine or a quarry site if you use a rectangular or triangular points grid to triangulate the area and create a TIN. Then, you can add breaklines and manual points to add more detail and make the TIN a more accurate portrayal of the terrain. It is always good to erase points that were dropped onto items or areas (due to the grid pattern) that you do not want to include in the TIN.
