3. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing File Formats Detecting Formats Fast decision which
format has been uploaded Does not read the whole file but a limited
amount of bytes Handle Compression Auto Detect which compression
has been used Various packing methods
4. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing File Formats Humminbird Supports multiple sensor in a
single recording Which sensor to choose ? Raymarine FSH does not
have an absolute time Impossible to do tide or gauge corrections
Precision of the position is bad since it must fit a 32bit number
Raymarine GPX suffers the same problems
6. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing File Formats NMEA 0183 Has multiple data sentences
for a single measurement Decision about which sentence to chose
must be made NMEA 2000 Has a rapid position update without time and
secondwise updates of position with absolute time
7. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing File Formats Lowrance SL2 Precision of the position
is bad since it must fit a 32bit number Recorded data constantly
reveals multiple depths for a single position Bad position
resolution Garmin ADM Multiple tracks in a single file
8. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing Clustering Tracks - Scenarios A track file may
contain a single recording sequence That would be the best Multiple
tracks file may reflect a single recording (as done by the hardware
logger) A track file may contain multiple recording sequences (i.e.
Garmin ADM files)
9. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Preprocessing Clustering Tracks For statistical reasons it would be
best to process a single recording session and break the structure
of the files for postprocessing Variance of positions as per
recording session Associated error is isolated
10. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Considerations Errors in data Noise Jumping
positioning data Most sensors are Kalman filtered, so this problem
is usually not a problem when the ships move Systematical Errors
Drift in Depth Sensor measurments
11. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Real world errors Low speed error At anchor High
speed error Water turbulence Currents Preceeding Ship caused water
turbulence
12. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Sensor Positions Depth sensor is mounted below the
waterline User has to provide that information Consider GPS offset
to the depth sensor
13. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Gauge corrections Gauge values are available online
User may create gauges where no official gauge is present and
measured online Gauges may span undivisible sections of rivers
Multiple Gauges need a common measurement base Some Rivers have a
form of equalized water level
15. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Ocean corrections Water Depth to LAT Use DTU 10 Tide
Model for Mean Sea Level Calcalute offset values to LAT by
calculating 19 year minimum Online water level correction during
filtering
16. OpenSeaMap Developer Meeting 2015 Jens Kbler Track
Postprocessing Ocean corrections Water Depth to LAT
17. OpenSeaMap Developer Meeting 2015 Jens Kbler Calculating
Contours Considerations Worldwide calculation required Depth
measurments constitute a highly irregular grid Official measurments
usually are regular Crowd source data is sparse This is a
multivariate interpolation
18. OpenSeaMap Developer Meeting 2015 Jens Kbler Calculating
Contours Multivariate Interpolation Partionized Constrained
Delaunay Triangulation Idea: OpenStreetMap inshore waters are
already partitionized Use the partitions to execute a single
triangulation with the borders as constraints to the triangulation.
Islands form constraints as holes. OpenStreetMap Water polygons
provide the same information for oceans Gebco 100 depth line
declares outward boundary
19. OpenSeaMap Developer Meeting 2015 Jens Kbler Calculating
Contours Partionized constrained delaunay triangulation : Example
in the Adriatic Sea
20. OpenSeaMap Developer Meeting 2015 Jens Kbler Calculating
Contours Partionized constrained delaunay triangulation : Example
in the Adriatic Sea
21. OpenSeaMap Developer Meeting 2015 Jens Kbler Calculating
Contours Partitionized Contours need to be remerged again Find
bordering water polygons that have a contour line Merge the contour
lines together to form a single contour line that spans the
partitions