Surveying has been important for decision-making since ancient Egypt, where it played a key role in tasks like defining property boundaries for tax purposes and managing newly acquired lands. Originally, surveying was completed using manual methods, such as with rods and chains, compasses, plumb bob and a lot of handwritten calculations to determine relative distances. Today, surveying fundamentals still have a core place in society, but this article is going to focus on lidar surveying. We have clients at NavVis who describe that some of their existing processes still rely heavily on graph paper to survey complex buildings.
From the NavVis blog.
Technology progressed until photogrammetry arrived, where terrain could be mapped using photos taken from the ground or from the air.
Then, in the late 1990s and especially from 2000 onwards, lidar scanning (LiDAR and LIDAR are also correct ways to write it) started to become the new standard for surveying. An abbreviation for “Light Detection and Ranging”, lidar uses lasers to scan the environment and represent it in the form of numerous data points.
This “point cloud” data collected using lidar is used to create detailed 2D and 3D maps including CAD linework, terrain and contour maps, Digital Elevation Models (DEMs), and various other models and visualizations of streets and buildings. This made it game-changing technology for land surveying.
Introducing lidar technology
An important lidar principle to remember is “time of flight.” The rapid laser pulses sent out from a lidar device bounce off the terrain and back to the sensor. The time of flight is how long it takes this laser pulse to make this round trip.
Knowing the time and the speed of the laser (which is the speed of light), a computer can then calculate the distance the laser traveled (distance = speed x time), which gives us the exact position that the laser bounced off of in the environment.
Note: The angle that the laser records the position from is equally vital to knowing the position for that laser pulse.
Take millions of these measurements, and the result is an accurate model of the environment surrounding the device. The “points of data” that are collected are collectively referred to as a point cloud: Everything you need to know about point clouds. When combined precisely with color data from cameras, a visualization of this data looks like this:
There are three key components of a lidar scanner to be aware of:
A laser source, which emits near-infrared lasers, sweeping the environment, tracking the angle of the laser and
A laser receiver recording the reflected laser pulses
Timing and positioning systems, such as a GPS or IMU (Inertia Measurement Unit).
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