What is a scene?
A scene is composed of multiple scans captured sequentially one-by-one at a number of scan points.
Each scan is automatically aligned against one of the previously captured scans.
What is scan alignment?
Scan alignment assumes computing relative orientation and position between scans so that their common parts match each other.
Walls are doubled and superimposed over the floor
The scene matches real-world geometry
The new scan is always aligned against the scan marked by a large blue point. It can be selected by tapping on it on the map. By default, the last scan is always selected.
For example, you can scan a bedroom and a bathroom and then return to finish scanning the hall, as on the image above.
Keys to good scan alignment
Scan alignment is done automatically. For it to be successful, you should always guarantee good visual intersection between the two scans that are being aligned. In particular:
1) Keep scan points within the 5-7 ft (1.5-2 m) distance range from each other.
2) Always do a scan from a doorway when entering a new room. Otherwise visual intersection between the scans is blocked by the walls.
Visual intersection is small due to depth sensor limited range and occlusion by walls
Visual intersection is large due to the scan point in the doorway
Scan alignment issues
If the above recommendations are followed, you will get correct alignment and a solid line between the scan points on the map. A solid line indicates reliable alignment (though it is not a 100% guarantee, see Bad alignment).
But some spaces might pose additional difficulties for the scan alignment algorithm. In particular:
- outdoor areas
- large empty spaces
- narrow corridors
- areas without textures
- areas with repetitive elements
If the app fails to determine the position of the new scan, you have to reshoot the scan. The best practice is to move closer to the selected scan point to increase visual intersection.
Sometimes the app would accept an alignment but its confidence in it would be low. It often happens when scan points are too far away from each other or during outdoor scanning.
In such case, scan points are connected with a dashed line. A dashed line indicates unreliable alignment and requires a visual check.
If alignment looks bad, the scan must be undone and recaptured closer to the selected point. For example:
If alignment looks good, the scan can be preserved, for example:
But it is still recommended to shoot an additional scan in the middle of the dashed segment to convert to solid lines:
Ideally, you should avoid dashed lines and have only solid lines on your map.
A visual check is essential, especially when scanning outdoor areas, large empty spaces, narrow corridors, areas without textures or areas with repetitive elements. A solid line between scans is not a 100% guarantee of alignment correctness.
In some rare cases, misalignment might happen without any warnings or errors being raised. The only way to notice it is to check the position of each new scan visually by matching it to the real space.
In case of misalignment, you should undo the scan and reshoot closer to the selected point.