Surveyors and GIS professionals have the highest standards when it comes to their tools and their trade. It’s no wonder that many surveyors are turning to drones for their mapping and 3D modeling needs. Surveying drones consistently achieve results that meet survey-grade accuracy standards, and in comparison with traditional surveying techniques, drones drastically reduce the time, cost, and effort required.
Surveying with drones is more complicated than snapping a few photographs from above. There are several steps required, from preparing ground control points, to mission planning, to process the images you capture with surveying software.
Oftentimes surveyors are commissioned to produce high-resolution orthomosaics constructed with photogrammetry techniques or 3D models created with oblique cameras and 3D surveying techniques.
What is oblique photography?
Within drone surveying, a technique that has seen success in 3D modeling is the use of oblique photogrammetry, where images are captured by several lenses. These multiple lenses are mounted together in an array with fixed axis angles. The resulting images reveal details that are sometimes missed when only capturing vertical photographs, such as features occluded by vegetation or tall structures.
Oblique camera systems use a mechanical rig with five cameras in fixed positions in a cross configuration; one camera in the center is surrounded by four other cameras, in front, back, left, and right, equally distanced at 90-degree intervals. This system places the central camera at an oblique angle where the ‘nadir’ angle (the point directly below the camera at ground level) is at a known, fixed point in the image.
Benefits of oblique photography
The requirements for accurate 3D models are ever-increasing. For example, within urban mapping, 3D models are used for space management, energy requirement analysis, traffic and pollution monitoring, and disaster management. In surveying, an accurate 3D model can identify potential problems early in a project’s timeline.
When compared with vertical aerial photography, oblique photography has many benefits. While a vertical angle can help show the placement of features like buildings, streets, or open spaces in relation to each other, oblique aerial photos are better at giving perspective of the appearance of features that rise from the ground like buildings, topography, foliage, etc in relation to the ground and horizon.
Some more benefits of oblique photography include:
Images captured with an oblique camera reveal details that otherwise may have been obstructed in the vertical view by foliage or tall buildings.
Oblique photography makes it easier to accurately determine the elevation of features when compared with vertical aerial photographs
As opposed to an orthographic setup, where the central camera looks directly down, the oblique system captures far more of the relative height data ahead of it. This also negates any lens distortion in all directions around the focal point, which the orthographic method could often suffer from.
Using multiple shots at controlled intervals, the position and relative height information gathered from each dataset can be compared, contrasted, and then amalgamated to give the relative height information between elements in the target area, producing a map of both position and height data, which can be rendered as a 3D map of the area surveyed.
And now, using KML, and angle compensation accessories, reduce lots of photos before modeling. Improve the efficiency to a new level.