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How to 3D Map underground environments with a Handheld Scanner

Posted by Sean Higgins on 2/27/20 9:34 AM

Underground environments like tunnels, caves, mining sites, and basements are complex. This makes them an ideal application for handheld 3D laser scanning tools, which can capture all of the cracks, crags, twists, and turns you need to measure—not to mention let you make your measurements back in the office.

Handheld laser scanning does present a few challenges in these environments, but these challenges are simple to overcome if you understand a few basic points. In this article, we’ll cover everything you need to know to get a good quality scan, including what to look out when you're scanning, and some best practices to guide you in your planning.


Factors that affect your scan

Lighting

This one is simple: your scans will only be as good as your lighting. Since the light in underground environments is often dim and uneven, you can improve your data quality by making the lighting brighter and ensuring even coverage. This will produce scans with higher resolution, lower drift, and reduced noise.

Check out our support article for an example of an inexpensive light you can use to improve the lighting in any underground space. 

Below are two underground environments. The one on the left is poorly lit for scanning, and will return bad results. The one on the right has bright, continuous, and high intensity lighting, which will return very good 3D scans.

Underground-scanning-lighting-exampls

 

Width

If the tunnel or cave is relatively narrow (less than 3m or 10ft), you may experience tracking loss while scanning with a handheld scanner. But only if you don’t pay close attention to technique.

In narrow environments, it is crucial to plan your whole walking route before you begin scanning. Through testing, we determined that the best practice is to perform loop closure—which involves taking the scanner back to an area you’ve already scanned—for every 25m you scan. Divide the scanning space, capture the data and then register all the point cloud files together.

For more information on loop closure, please read this support article explaining the process in greater detail.

Underground-Scanning-width-examples

 

Height

Just as narrow tunnels can cause tracking problems, tunnels or spaces with low ceilings can do the same. 

If you scan in an environment like this, it is very important to keep the scanner in a steady position throughout the capture. If the scanner is not stable in its position while you’re moving, then it is likely to produce drift and noise in the data, like you can see in the image below.

Underground-Scanning-Bad-Data

 

Movement

If there are a lot of people or vehicles moving through the environment—or any other kind of activity—this will make scan tracking difficult and can result in an unnecessary noise in the data. For example, if a person walks alongside you while you scan, this will leave small traces on the point cloud data.

Best Practices

As you can see, you are much more likely to get good results if you scan carefully and plan ahead of time.

To help make sure you’re covering all the bases, here is a list of best practices to follow next time you are scanning a complex underground environment. (Click on the links to view support articles for more information).

  1. Plan your route
  2. Divide the scans
  3. Hold the scanner properly
  4. Perform loop closure 
  5. Learn how to turn while scanning
  6. Register the scans
  7. Mount the scanner properly if you are using it on a vehicle
  8. Bring your own Lighting

 

Topics: How To