When surveying a very large area that contains a variety of environments, you need to combine multiple Virtual Surveyor workflows to produce an authentic survey-grade map.
As each dataset has its distinguishing features, there is no optimal workflow to survey large areas. Nevertheless, there are three common steps you repeat when working on each area:
- Break up the area into different parts depending on their common terrains.
- Use a specific Virtual Surveyor workflow for each part that is best suited to model the terrain.
- Triangulate the separate surveyed areas into one unified CAD model.
In this article, you will see work on a quarry site—that was mapped by drone—to deliver an extension of the site survey. The dataset includes open and wooded areas. The site also includes some haul roads and ponds. Conventionally surveyed data is also incorporated into the final survey for areas where the drone could not see through the vegetation.
- Area Classification for Large Maps
- Choose a Suitable Workflow for Each Area
- Complete Your Survey with Lines and Points
- Create Your Survey Surface
- Export to a CAD Model
Area Classification for Large Maps
The first step to large area mapping is to identify and divide your survey into common areas. This makes it much easier to organize and work on each section of your survey area.
- You can first divide your drone survey based on the coverage and what you can see on the Image Terrain.
- It's also good to consider the current use of the sites along with their future uses.
- Some areas require a more detailed survey while others can be modeled with a simpler survey.
In this example, you want to survey the quarry and its surroundings. After a quick review of the Image Terrain, you can divide the quarry into six different types of areas.
RED: an operation area.
BLUE: settling ponds.
YELLOW: a future stockpiles area.
GREEN: a wooded area.
WHITE: a wooded area that was surveyed using the traditional method.
Choose a Suitable Workflow for Each Area
When there is little to no vegetation coverage or any kind of noise in the Elevation Terrain, use Q-points to detail the terrain. It often helps to combine the smart point grid with a Rectangular/Triangular Point Grid to create uniform surfaces.
For this quarry, you can define two open areas to make use of this workflow: the operation area and the future stockpile area.
- The future stockpile area may require some cleaning before starting the survey.
- Due to the running operations in this situation, there are multiple machines and obstacles shown on the drone survey.
- Before using the point grid tools, use the Remove Object and the Replace Terrain tools to remove these objects and clean the terrain.
For any future stockpile areas, you want to deliver a reference surface that is used during future stockpile calculations. In this case, there are some existing stockpiles from the previous operations.
- It's probably easiest to run a Rectangular Point Grid and then remove the points that fall on top of the previously existing stockpiles.
- Draw boundaries at the bottom of the stockpiles and use the Select Within tool in the TOOLS menu of the selected boundary to select and delete any unnecessary points.
Heavily vegetated areas are often challenging to survey with drone data but can be mapped using the Low-Pass Point Grid. The wilderness area—outlined in magenta—next to the quarry, is a good case of best practice to use a Low-Pass Point Grid. This method can be a more efficient (and faster) way of surveying since your grid model is completed once you have manually removed any remaining points on isolated trees, bushes, or other vegetation.
- There are some unexpected obstacles or vegetation that you need to remove points from.
- Simply delete points over areas where the ground cannot be surveyed since you do not know what is actually under the vegetation canopy.
- Only survey what you know is there.
In general, a heavily vegetated area can be surveyed using the Low-Pass Point tool since the other grid tools have a harder time measuring between the open areas of the tree canopies when there is a lot of "closed" or "hidden" terrain.
- Manually add or remove points where you can see or use terrain the Low-Pass tool might have missed.
- You could also use the Rectangular/Triangular or Low-Pass Point Grid tool to map the forest at the entry of the quarry or even use the Point tool if it is faster in a small enough area.
Photogrammetry generally creates "noisy" surfaces over water bodies.
- Each pond needs to be flattened.
- Draw boundaries around the ponds using Extract Level.
- Map the area with a Rectangular/Triangular Point Grid and erase the points located within the smaller boundaries.
You use this method to map the ponds that are settling within the area (blue outer boundary).
No Data Area
Sometimes, it's impossible to determine the ground level with drone data since the area consists of a "closed canopy" of trees. For these areas:
- Import terrestrial survey data into the project to complete your surface.
- Collect your terrestrial data with a GPS, total station, or other traditional survey methods.
- Import the terrestrial data as a CSV file.
The points that are uploaded from a field survey are used in the same manner as any other point that is generated in the software.
The forest in the middle of the quarry has a closed canopy, so a traditional topo survey was created and uploaded instead of only using the drone data. You can add the points from this survey as a CSV Point File by using the Drag and drop function in Virtual Surveyor.
Complete Your Survey with Lines and Points
To improve the detail of your survey, you can add breaklines wherever they may be required.
- In areas with pronounced topography, add some breaklines to make sure the TIN model accurately represents a model of the terrain.
- Activate the Guided Breakline Tool to quickly add breaklines on the top and bottom of the slopes.
- Use the Drawing Tools to trace hauling roads.
- You can always manually add points in locations where you see it is necessary.
Create Your Survey Surface
When you are done surveying, you can use all the generated survey items to create a lightweight surface model.
- Use the Triangulate All function to generate a TIN surface.
- You can Display the contours on that surface and enable other project items to showcase your work, depending on what you want your map to show.
Export to a CAD Model
When you are 100% satisfied with your survey, you can export it as a CAD file.
A special thanks to the Walbec Group for letting us use their data!