Introduction
Problem description
A Dataset in NavVis IVION Processing can be blocked when the surveyed control point locations do not match with the captured control point locations during the scan. Here are several common error sources that may appear when processing with control points.
A blocked dataset will give the following feedback within the NavVis IVION UI :
This blocked state can be resolved directly within the UI by opening "View control point configuration". This will show the following view:
Deselect the control points identified as incorrect. A check in the background assumes the easiest mistake made in the current configuration: one control point is misaligned because it contains a typo or was surveyed incorrectly. While this assumption is often true, it can be a more complicated error source causing this identified misalignment, especially if several control points are marked as incorrect.
A sign that a more complicated error in control points is causing the behavior is when only two control points are identified as being correct. This is due to the fact that the minimum of 2 control points lying on one geometric line often enough matches well enough, even if there are significant problems within the control point file.
Scope
This solution applies to all versions of NavVis IVION Processing.
Troubleshooting procedure
Follow these steps when trying to resolve the "BLOCKED" status of your dataset:
1 Go to "View control point configuration"
The detected differences in control point locations will be depicted on the map when hovering over the respective control point. You can use this view to get a better understanding of the mismatch. Yet, this view can sometimes be misleading. To go forward, do the following:
If only 1 control point is identified to be problematic, deselect it and continue processing. If the processing succeeds, check if the georegistration of the dataset is as expected and check its quality map for any problems like double walls or unexpected bends in structures. Another error causes these problems. Continue with the checks described later in this article.
If multiple control points are identified as incorrect and all remaining correct ones lie on one rough geometric line, continue debugging. Deselecting those control points without understanding the underlying issue will likely not bring the expected results.
2 Compare the control points captured during the scan to the ones surveyed and provided via the control point file
Most often, the source of blocked datasets is a control point file that is set up incorrectly. To compare the control point locations, open the following files:
The control point locations captured during the scan in the file
/datasets_rec/<dataset_id>/anchors/anchor_poses_recorded.txtThe control point file uploaded for processing
The quality map of the scan to understand the capturing locations
Check:
All control point IDs/names match (incl. upper and lower case letter).
No doubled location entries exist in the control point file (e.g. copy & paste error with 2 different IDs in the same location).
No unexpected doubled ID/name in the scanned control points (e.g. a control point named incorrectly with the name of another one).
No control point locations further away from the dataset than other control points.
Accuracy of control point values (e.g. typos in decimal points).
All those issues are caused by typos when transferring the georegistrated surveys control point coordinates to the NavVis compatible control point file.
3 Compare the relative distances between surveyed and scanned control point locations
In the following files:
The control point locations captured during the scan in the file
/datasets_rec/<dataset_id>/anchors/anchor_poses_recorded.txtThe control point file uploaded for processing.
Check for diverging relative distances between points. If points A and B exist in ~3m difference in the scanned data, they should exist in ~3m distance in surveyed data and vice versa.
A consistent factor between those 2 relative distances indicates that a non-metric unit system was used. A NavVis compatible control point file must only contain values in the metric system.
A mismatch only for one pair of control points indicates that either a typo was made in the control point file or that the SLAM broke during the scan. The latter can be checked by looking for unexpected jumps, twists or shortened/prolonged trajectories in the quality map of the dataset.
4 Compare the coordinate system orientation of surveyed and scanned control points
When uploading a control point file in NavVis IVION Processing, the file will be checked if it contains control point locations in a right-handed (NavVis standard) or a left-handed (not supported by NavVis) coordinate system. The tool will automatically transfer from an incorrect left-handed system to the necessary right-handed one if the left-handedness is successfully detected. This is only possible if control points are well distributed within the scan and are not aligned on one rough geometric line.
You can compare the orientation of these two coordinate systems by drawing two simple coordinate systems for X and Y on a piece of paper and transferring 3 control point pairs into those. These 3 points should span a triangle with similar side lengths and angles. Once drawn, check if the 3rd control point lies in both drawings on the same side of the vector connecting the 1st to the 2nd point. If this 3rd control point lies on different sides, you have likely used a left-handed coordinate system and this left-handedness might not have been correctly detected within our software. To correct this, transfer the control point file to a right-handed-coordinate system.
In georegistration context, the X, Y, Z coordinate system that NavVis uses is resembled by Easting, Northing, Height.
5 Process the dataset without control points
If you cannot identify the problem's source, process the dataset without uploading the control point file. The dataset then needs to be manually aligned with NavVis IVION’s Dataset Alignment functionality.