W W W . K A A R T A . C O M
1 0 2
Verify that you initially acquire a signal prior to entry, and that you can reacquire signal
after exiting an obscured area. At a minimum, make sure to anchor your trajectory with
good quality GNSS at beginning and again at end. Any points that can be acquired during
scanning, even intermittently, can assist with PPK correction. For expansive GNSS-denied
areas with no satellite signal, the use of Ground Control Points (GCPs) may be warranted.
W a i t 4 - 2 4 H o u r s f o r C O R S R e s u l t s
Availability of CORS data can be hourly or daily, dependent upon station type. Waiting at
least one day/24 hours guarantees you will get data from all available stations. After 24
hours, you can still receive published data, but will notice diminishing returns as you pass
the one-day threshold.
U t i l i z e G N S S C o r r e c t a n d A l i g n w i t h G N S S
Use the GNSS Correct processing task to pull data from your respective network. If using
your own base station instead of the CORS network, you will select the appropriate file.
See GNSS Correct on page 72 for detailed instructions about this task.
Once you have retrieved data, you can review it for quality prior to doing any additional
processing.
R e v i e w T r a j e c t o r y
After running GNSS correct and alignment with GNSS, open the trajectory in
CloudCompare (from the File Mgmt tab of Scan Details; see File Management on page 49
for more information) and verify the percentage of fix 4 and fix 5 in your data, as well as
their locations. You can do this by setting the Scalar Field’s Active to "fix quality" and
viewing the different point types (1, 2, 5, 4). Ideally, using only fix 4 data would be the
most reliable quality. However, you may need to include fix 5 (or fix 2) in certain driving
scenarios or in cases where fix 4 data were not a high percentage of your results.
When reviewing the trajectory in CloudCompare, also look for any z drift (elevation)
issues, by viewing from the side. You may see noise even with fix 4 or fix 5 (due to
reflections or areas under structures) which manifests itself as rogue points above and
below the trajectory. Use the Maximum HDOP and VDOP parameters during replay to
eliminate noisy fix 4 and fix 5 points from your dataset. You can compare the
gps.ply
(live
scan data) and the gps_ppk results to see the effect of the corrections. You will see z-drift
errors if fix1 or fix 2.