when good 3d scans go bad

Here are six ways 3d scanning services may not go as expected, and how you can avoid them.

1. Misguided alignment

Here is the situation. You are the plant manager at a natural gas compressor station and you need to design some new piping and equipment to be installed. You hire professional 3d laser scanning service to capture the as-built plant into a 3D point cloud. They do the work and deliver to you a beautiful point cloud. But when you try to import that point cloud into your CAD program, things are not lining up. You think, “not a problem, I can just rotate the point cloud and shift it into place”, right? Well unfortunately it is usually not so simple. Aligning a point cloud to a CAD model can take some effort and is usually not a trivial “no-brainer” type step at the end. It is best to define the desired alignment in advance before having the scanning done. Sometimes there are easy ways to capture reference points during the scanning itself that can make alignment quick and easy. Other times it is necessary to utilize survey equipment and techniques to achieve the desired alignment. But even it the only possible solution is to rotate and translate the CAD model to best fit the drawing, it will likely be easier for your 3D laser scanning service provider to do it, and it is best for them to know in advance so they only have to do it once.

2. Fuzzy details

Let’s say you purchase 3d laser scanning services and receive a beautiful point cloud of your football stadium. With that point cloud you can virtually measure the distance from any two seats, or plan the path that the cheerleaders will enter and exit, or find the optimum placement of a stage for the band. But let’s say you also want to analyze the support structure that the stadium lights are affixed to. You look closely at the points and you just can’t make out a discernable shape for the structural steel. Unfortunately the scanner was too far away to “paint” the steel with enough points to make out the details. It could be that the 3d laser scanning service provider was unaware that you were so interested in the lights. It is generally understood that the 3D laser scanner captures everything it sees, but it is still necessary to understand which items in the environment that you are interested in so that they can make sure and get good coverage of that spot. So communication and planning before the job starts is essential. 

3. Missing in action

You get a scan of the reactor room of your
nuclear power plant. While the environment is safe for humans, no one wants to
hang around a nuclear reactor core for too long, which is why 3D laser scanning
services make sense due to the speedy data capture. After the scan is complete
and you see the results, you notice that the reactor drain plug is missing from
the scan. It fell in a “shadow”, something that always occurs with 3D laser
scanning services. The scanner scans all that it “sees”, but if something is
blocked from line of sight by an obstruction, it is in a shadow and won’t be visible
in that point cloud. 3D laser scanning service providers circumvent this
problem by taking many scans from many vantage points, reducing the number of
shadow to acceptable levels. The best way to avoid your critical item fro being
in a shadow is to walk through the job in advance with the 3D laser scanning service
provider and identify anything that is of interest to you. Some will go as far
as placing tags or flags on the items to make sure they don’t get forgotten. 

4. Rained out

Don’t let bad weather ruin a 3D scanning day. Proper weather planning makes it less likely to end up having to stop scanning due to rain or snow. Wind can be a factor two sometimes, if it blows the tripod too hard. There are water resistant 3D laser scanners out there, but who wants to risk putting your extremely expensive scanner out in the rain? You should agree on a “stand-down rate” in case something weather-related comes up and the 3d scanning services team needs to stop for a while. It also may help to leave a little flexibility in the schedule, if that is possible. 

5. Unstable situation

Unstable situation. You are scanning a cooling tower on a hot day. You put the tripod on some hot asphault and conduct the scan. Later you realize that the scan just doesn’t line up with the others nearby. Why? The spikes from the tripod settled into the hot asphalt, which had become soft due to the high temperatures. The moral of the story: if the scanner moves, or the subject moves during scanning, the scan is no good. Make sure the environment in which the 3D scanning service is taking place is solid. Wood floors and even catwalk floors have a tendency to flex when walked upon and can be unstable. Soft ground requires extra care to make sure the tripod is firmly planted. These are all things that your professional 3d scanning service provider will know, but it is good to be aware of them so you are not setting yourself up for failure. 

6. Scale to Fail

You order 3D scanning services for your barn, but when you receive the results the are 40X too small. What happened? Isn’t 3D scanning supposed to be accurate? Fortunately, 99% of the time the scan is indeed accurate, but somehow the program you opened it in thought that the 3D scanning services were done in different units than it was. For example, the scan may be in meters, but if your CAD program opens it expecting the units to be inches, we have a scaling problem on our hands. The best was to avoid this is to agree on units in advance, because even though it is a fixable problem, it is sometimes a bit of a hassle to have to re-export everything, and transferring all of those large files again just adds delays to your project.

Keep reading: more articles about 3D scanning

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