When surveying a very large area containing varied environments, you need to combine multiple Virtual Surveyor workflows to produce a survey grade map.
As each dataset has is own distinguishing features, there is not one optimal workflow to survey large areas. Nevertheless, there are three common steps you repeat when working on each area. Firstly, you should break up the area into different parts depending on their common terrains. You can then use a specific Virtual Surveyor workflow for each part that will best model the terrain. Finally, you will triangulate the separate surveyed areas into one unified CAD model.
In this article, we work on a quarry site which has been flown 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.
- Identify all the areas depending on their uses and their features.
- Apply a specific virtual survey method for each of those areas.
- Complete your survey with lines and points.
- Compile your survey map.
- Export your map.
The first step in large area mapping consists in identifying and dividing your survey into common areas. You can first divide your drone survey based on the coverage and on what you can see on the orthophoto. Also consider the use of the sites and eventually their future allocations. Some areas require very dense survey while others can be model with a less stringent survey.
In our current example, we want to survey the quarry and its surroundings. After a quick analysis of the orthophoto, we divide the quarry into 6 different types of area.
RED : an operation area.
BLUE : settling ponds.
YELLOW : a future stockpiles area.
MAGENTA : wilderness.
GREEN : a wooded area.
WHITE : a wooded area which has previously been survey with traditional method.
Choose the suitable workflow for each area
When there is little to no vegetation coverage or any kind of noise in the elevation terrain, use the Q-points. Often, it helps to combine that smart point grid with a regular point grid to create uniform surfaces.
For our quarry, we defined two open areas to employ this workflow : the operation area and the future stockpile area.
The operation area, surrounded by the red boundary, requires some cleaning before starting the survey. Indeed, due to the running operations, there are many machines and obstacles on the drone survey. Before going further with the point grid tools, the Remove Object and the Replace Terrain tools are used to remove these objects.
For the future stockpiles area, we want to deliver a reference surface that will be used during future stockpile calculations. Unfortunately there are some existing stockpiles from previous operations. We run a rectangular point grid and then remove the points that fell on top of those stockpiles. We draw boundaries at the bottom of the stockpiles and use Select Within tool in the SELECTION TOOLS menu of the selected boundary to select and delete the unneeded points.
Challenging vegetated areas can be mapped using a regular point grid and manual cleaning. Typically there are some unexpected obstacles or vegetation that need to be cleaned. This can be done by removing points over areas where the ground cannot be surveyed.
For the wilderness area, surrounded in magenta, next to the quarry, we use a rectangular grid. The process is completed with manual cleanings to remove vegetation areas or points on isolated trees, bushes, or other vegetation.
In general, a densely vegetated area can be surveyed with a low-pass point grid. We utilize this tool to map the forest at the entry of the quarry (green boundary).
In general, photogrammetry 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 regular point grid and erase the points located within the boundaries. We use that method to map the settling ponds area (blue boundary).
No data area
Sometimes it's impossible to determine ground level with drone data. For these areas you can import terrestrial survey data into the project to complete your surface. Your terrestrial data can be collected with your GPS or total station, or other traditional survey method. It can ideally then be imported as a CSV file. The points will then act as any other point created in the software.
The forest in the middle of the quarry has a closed canopy. A traditional topo survey was created in lieu of the drone data. We can add the points from this survey as a CSV point file by using the Add Data Control menu.
Complete your survey with lines and points
To improve your survey, you can add some breaklines where required. In areas with pronounced topography, add some breaklines to make sure the TIN model will accurately model the terrain. You can activate the Guided Breakline Tool to easily digitize these breaklines. We also use the drawing tools to trace haul roads. You can also manually add some points in locations where you feel it is needed.
Create your survey surface
At the end, all the survey items should be active to create a lightweight surface model. Use the Triangulate All to generate the TIN surface. You can Display the contours on that surface and enable some other project items depending on what you want to show on your map.
Export to a CAD model
When you are 100% satisfied with your survey, you can export it as a CAD file.
Special thanks to Walbec Group for usage of their data.