Carl's notes

Having spent a long night calibrating Ubisense, here is a checklist to make it faster next time. This is with version 2.0.4 of the software. Many thanks to our resident surveying expert Yukang for staying very late to help me out with this.

Doublecheck offsets to apply to surveyed points. Get signs right. Remember which points were surveyed with the reflector pointing up or down, take into account the height of the totalstation.

Take into account the height of the antenna inside the tag. This may add 1-2 centimetres to the height of surveyed points.

Check that the antenna boards inside the sensors haven’t come loose. If they have you need to open the case and clip them back into place.

Check that the sensors are horizontal, roll should be zero.

Optimal pitch of the sensors is 45 degrees downwards. I seem to not point them down enough so should try to emphasise this in future.

Choose calibration points that are within good line of sight to the sensors. Avoid points that are directly on the metal floor panels. The best position for determining orientations is directly along the boresight of a sensor.

Survey some extra points on the walls and pillars. These can be used to align future surveys to the initial coordinate system.

The tool to use for calibration is called the Location Engine Configuration tool.

Don’t use the full calibration. You’ll get a much better idea of what’s happening if you do several rounds of dual calibration, orientation calibration or offset calibration. Dual calibration may save time because it gives orientation estimates for 2 sensors simultaneously. Make a note of the values for pitch, yaw and cable offset. Do this several times for different surveyed points. Save the results into a spreadsheet or Matlab and plot them. This will allow you to decide whether the data is consistent enough to just take the mean values or whether you need to remove outliers or even use different points.

When doing several rounds of calibration at the same point you can save time by clicking back in the result window, this will immediately trigger a new data collection. However if you attempt to click back twice to choose a new point part of the server will crash and the GUI will freeze. If this happens use the service manager to restart the calibration server. To avoid this in the first place don’t click back twice but instead use cancel when you want to calibrate using a different point.

When values have been entered for yaw, pitch and cable offset for all sensors the system should be ready to run. If the AOA and TDOA measurements are displayed correctly but the position of the tag doesn’t appear make sure the ceiling, floor and max std error values are correct in the cell properties. Ceiling and floor should be set to the height of the ceiling and floor in your coordinate system, zero seems to make the software filter out all position estimates. Max std error can be set to 0.05, if it’s set to zero all position estimates will also be filtered out.

Press ctrl-shift-a to see extra information in the Location Engine Configuration tool, including the trace of past position estimates and the number of sensors used in each estimate.

We’ve had problems with tag batteries so we tend to remove them when not in use. You may prefer to disable monitoring of the cell and reduce the measurement rate. The slowest measurement rate seems to be once every 8192 slots, slower values aren’t accepted even though they appear in the drop down menu.