When it comes to documenting a project in 3D, you may find yourself comparing laser scanning and photogrammetry as possible solutions. Both technologies exist to achieve similar results, however depending on the scale of your project, desired level of accuracy and your budget one will typically be a better choice than the other. In some cases a combination of the two can produce the most desirable outcome.
So let’s break both technologies down and establish what applications each is best suited for.
Laser Scanning
On one side we have laser scanning, which has been around for decades. When it finally found its way into construction, architecture and engineering there was much excitement over the accuracy and speed of the new technology. Computers are finally advanced enough to handle the sheer volume of data the scanners produce usually in the form of point clouds.
Essentially, the laser scanner works by sending out hundreds of thousands of light pulses and measuring the distance between its location and the objects the light pulses hit.
Photogrammetry
In its rudimentary form, photogrammetry has been around even longer than scanning. By simply knowing the location a picture was taken and the size of a reference object in the image, the position and size of objects can be calculated using triangulation. In 1999, David Lowe of the University of British Columbia developed a robust triangulation algorithm that launched photogrammetry into its modern day form, greatly increasing its accuracy, speed and applicability to various industries.
Digital photogrammetry today works by taking many images of a scene from different locations using standard digital cameras, even smartphones, and then processing them through programs to determine the exact location from which these photos were taken. When the positions of the camera are known, specialty software looks for common points in two or more photos to determine where objects exists in 3D space.
Comparison
Whenever there are multiple tools to get the job done we have to step back and weigh the differences. Accuracy, speed, costs, scale and the final use of the 3D data need to be considered when choosing between laser scanning and photogrammetry.
Below is a simple pro’s and con’s chart for both techniques followed by a discussion of favorable applications for each technique.
Laser Scanning
Pro’s
Accuracy within ¼ of an inch for most scanners
Accuracy over large spaces
The error rate is fixed based on the capabilities of the equipment
Automated process after targets are placed and scanner is started; less chance for user error Less time spent on site
Availability of auto-extraction / meshing software for point clouds
Con’s
Equipment can be prohibitively expensive to own
Generally need to upgrade physical equipment to keep up with progress
Fuzzy point cloud on highly textures / reflective surfaces
Photogrammetry
Pro’s
Significantly cheaper equipment Most improvements are on the software side so no need to buy new equipment to keep up with progress Better visual representation of textures
Con’s
Accuracy is lower than laser scanners over large space
Scale limitations based on camera lenses maintaining clarity over long distances
Less automated process allows for more user error – results depend greatly on the experience of the operator
More time spent on site
Auto extraction / meshing software is not as advanced
Errors when dealing with reflective/transparent surfaces
Take Away
To summarize, when deciding between laser scanning and photogrammetry, the main questions you need to ask are:
- How much accuracy they really need?
- What the data will be used for?
- How easily can the data can be collected?
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