New users will often struggle with "losing tracking" while scanning. This is actually a very important feature of the software that prevents the user from capturing any low quality data that the software doesn't trust, but it can be frustrating to new users just picking up the technology. The following scenarios can cause you to lose tracking:
1. Lack of points visible to the depth camera (e.g. due to sunlight).
2. Getting too close to the subject.
3. Moving too far away from the subject.
4. Moving too quickly.
5. Tripping, or otherwise jerking the camera.
6. Pointing directly at featureless areas such as empty white walls.
7. Lack of background geometry (i.e. empty space behind what you're capturing).
8. Movement in your scene (i.e. someone walking through).
Note: If you are using an Intel RealSense L515 sensor the most common cause of tracking loss is too much ambient sunlight in the scene. This causes the sensor to struggle with depth measurements. In that case, try to block out as much sunlight as possible from the scene, e.g. by closing curtains or using shutters / blinds.
Luckily there are a few simple tips and tricks that can make a huge difference for almost every scene:
Tips for Maintaining Tracking:
1. Pay attention to the scene fitness bar (green circle around the start/stop button). This indicates how well the device is tracking in relation to the geometry it is seeing at any point in time. You'll want to pick a point of good scene fitness to start and finish your scan (i.e. corner of a room), and also watch the keep an eye on the fitness bar throughout your scan. If you see it going down close to 0, you should consider backing up and/or approaching the area from a different path. This indicates a challenging area (such as an empty white wall), and should be a warning that you may lose tracking soon and need to back up to where you last were.
2. Generally point the device orthogonal (straight on) to the target, unless you are seeing low scene fitness. In this case you should back up and/or approach from a different angle to include more geometry in the sensor frame.
3. Whenever possible, maintain a distance of 3-7 feet to the target with the DPI-10 (2-12 ft range) and 2-5 feet with the DPI-10SR (1-6 ft range). New users will often find themselves feeling like they should get in very close to the areas of interest, which will often result in loss of tracking. The sweet spot is actually the 3-6 foot range, which will not only help with data tracking but also likely improve your data quality. You do not need to get extra close to get good data.
4. Take advantage of background geometry. The more features/geometry the camera sees, the better this will track. Sometimes even areas that are unimportant to the capture otherwise can still be very helpful with tracking. For example, if you are scanning an object/equipment, you may want to place it in an area with walls/features behind it, which is counter-intuitive to the natural instinct to place it in the middle of an empty space.
5. Add targets/objects/texture to challenging areas. When you do need to capture the dreaded empty white wall or otherwise challenging featureless areas, it is recommended that you place some AprilTags in these areas. These will greatly help with tracking across those difficult areas. Other than AprilTags, adding objects or texture (colors) will also help, i.e. a box or a sign on the wall, although adding AprilTags will typically be the easiest and most helpful option.
6. If struggling to capture a difficult area, try capturing from further away first, then move closer for more detail if necessary. For example, if capturing a white wall, you'll want to start with the edges of the wall and then back up to fill in the bulk of it.
7. Capture an area of good scene fitness and/or with a few AprilTags in it first, and turn it nice and green. This will give you a good area to return to if you are ever struggling to regain tracking.
Tips for Regaining Tracking:
There are 4 steps for regaining tracking when you lose it. Please follow these in order:
1. Slowly move back to the area you were just in before you lost tracking.
2. Slowly move back to the next most recent capture area if you don't regain right away.
3. Slowly move back to another area of recognizable geometry / good scene fitness where you know you've capture good green data already (i.e. the corner of a room or piece of furniture/equipment, and/or an area with a few AprilTags).
4. If you are unable to regain tracking via any of the options above, you also have the option of closing your scan and restarting via the append feature (Scan>Append). This will allow you to select a previous frame position to reposition the scanner in, and continue from where you left off.
5. Lastly, please remember that if you lose tracking right away after starting a scan, you should probably just close out and start over! This will save you the trouble of trying to regain from only a small number of frames.
The following video tutorial will also help with these issues: