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U S I N G S E P A R A T E L Y L O G G E D D A T A I N T H E L O O P C L O S U R E T O O L
Stencil 2 uses an additional file to record GNSS trajectory with GNSS timestamps, Fix Quality, and
Dilution of Precision errors during the mapping/localization process when Stencil 2 is connected
to a GNSS unit. This allows seamless integration with the loop closure tool to enable global drift
correction in post-processing. This data can be any data point taken while collecting data as long
as the point can be correlated with the trajectory path and the time-stamp.
In addition to providing a method of using your own GNSS data logged separately, you could also
use any data generated based on a locally consistent coordinate system. An example of non-
GNSS data that can fit this model is data from a tracking theodolite that was recorded while
mapping with a reflector on top of Stencil 2. To use GNSS data logged separately or non-GNSS
data, the data will need to be formatted to fit the Stencil gps_202X-xxx.ply format.
The GPS_x, GPS_y, and GPS_z values are from the GNSS unit at the times shown. The key here is
to determine the time offsets between the Stencil 2 values and the GNSS values to create this
gps_202X-XX…ply file.
The UTM Zone information and the X, Y, and Z offsets applied to the GNSS data can be found in
the scan_info.yaml file. The vertex number is the number of lines containing the trajectory and
GNSS data.
pdop, hdop, vdop, and fix_quality are estimates of longitude, latitude, and vertical accuracy.
These may or may not be present depending on the NMEA messages output by the GNSS
system. These error estimates are used to filter out lower confidence values by the loop closure
tool and can be used to weight values for non-GNSS data by simulating accuracy estimates for
the loop closure tool.
An example .ply ascii file is shown below:
