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250 to do a rough approximation with faster results and see that your other parameters
are set correctly before doing a final alignment with closer points.
The Minimum Fix Quality uses the GNSS fix quality to eliminate GNSS points where the
quality is too low for use in alignment. You can choose between fix quality of Automatic,
(GPS) 1, DGPS (2), RTK Float (5), and RTK (4), in order of accuracy from least accurate GPS
to most accurate. For example, if you select fix quality of 5, processing will not include any
points with fix qualities of 1 or 2 but does include both 5 and 4 quality points.
The Maximum HDOP and VDOP Values use the Horizontal Dilution of Precision (HDOP)
and Vertical Dilution of Precision (VDOP) error estimates to eliminate GNSS points where
the quality is too low/noisy for use in alignment. Not all GNSS units provide this data
unless selected. The Minimum Fix Quality is the more standard way to select GNSS data
but setting the HDOP and VDOP values can be useful in some situations. Keep in mind
maximum
that the value is the
value, as this is an error term that gets larger as the
accuracy decreases. When 0 is selected (the default), this parameter is not used.
The Match Drift Distance is basically a sphere reaching in all directions from a point. The
parameter can be tuned for trajectories that do not cross but come close to each at
places other than the starting and stopping locations of the scan, optimizing where the
loop closure looks for potential matches. The default value is 5m.
The Loop Horizontal Search Range and the Loop Vertical Search Range set the radius
in meters to be used for matching where the two trajectories come close enough to each
other as identified by the match region. Setting the value larger will increase the post-
processing time. Setting it lower will reduce the search area for matching. The combined
Horizontal and Vertical of the Search Range can be considered as a cylinder around a
point.
Match Confidence Threshold is the confidence level below which Align will stop adding
scan frames to the current pose stack and attempt to match the pose stack back to the
registered map. Setting the number as low as 1 will add significant time to the processing
for larger datasets but may be acceptable when dealing with troublesome spots in the
dataset. Default value is 500.
The GPS Weight Factors (Horizontal and Vertical) allow you to change the relative
priority or importance of aligning a scan with the GNSS trajectory, as compared to other
factors like loop closure or trajectory continuity. Setting them below the default value of 1
will make GNSS alignment have less of an impact, while setting it above 1 the alignment
Keep in mind that if the GNSS
will attempt to follow GNSS trajectory more closely.
trajectory is of poor quality, increasing these weights can lead to significant distortion in
the resulting map.
You can specify a Preferred CRS (EPSG code) or preferred coordinate reference system
for your scan, using the coordinate system's EPSG code, if available and known to the
W W W . K A A R T A . C O M
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