OpenSeaMap-dev:En:Depth Data

This Page describes the necessary efforts to retrieve and analyze depth data as well as create renderings from it

Data Aquisition

Depth data can be retrieved from public domain sources or from crowd sourced data.

Crowd Sourced Data

Crowd sourced data may be gathered by YOU. There are two options in development. A hardware and a software option.

Hardware

We are currently developing a hardware logger that may easily be plugged to the ship's network in order to log the networks data to a SD card. That data may then be uploaded by plugging the SD card to a normal computer with internet connection for upload. The main goal is to support NMEA 0183 data with options for NMEA 2000.

Software

A Software logger is in development and can be retrieved [here]. It currently supports Bluetooth and serial ports retrieving NMEA 0183 data. IP Support and NMEA 2000 development is underway.

Data Preprocessing

Data Condition

Data is usually erronous and must be corrected

Internal data problems

Depth data may be affected by electrical conditions and software implementations

• Data is incomplete and fail their checksum (bus errors from physical transmissions errors)
• Data is erronous sensor data
  • Approximate correctable data i.e. invalid GPS position that may be interpolated
  • Uncorrectable data i.e. failed log sensor that shows slow speeds
• Data resolution is low i.e. for energy saving purposes GPS position is updated every 10 seconds instead of every second
• Sensor data is actively miscalibrated i.e. charter companies add additional draft to the sensor depth for safety reasons

External data problems

Depth data may be affected by different environmental circumstances

• The water temperature affects the ultrasound echo. An inhomogen water temperature yields unwanted echos
• The seabed affects the ultrasound echo
• The seastate affects the measurement. There even may be waves when there is no wind.
• Waves may affect the roll of the measuring vessel resulting in steep measurements that are invalid.
• The sounder sensor is not the position of the GPS antenna. A position offset including heading must be incorporated.
• The time of the measurement need not correlate with the time the position was received. This may even happen due to processing time of the hard or software.

Quality rating

Each record (time, positon, depth) should become a quality rating.

Points

Derived from the Fibonacci series.

Point	Description
1	extra small improvement
2	small improvement
3	medium improvement
5	large improvement
8	extra large improvement

Factors

Name	Factor	Description
depth offset	8 (extra large)	The difference between the depth measured by the echo sounder and the depth (waterline) measured by hand.
device distance	3 (medium)	The distance between gps antenna and echo sounder (lengthwise and crosswise).
SBAS	3 (medium)	Satellite based augmentation system (WAAS, EGNOS, MSAS) which allows to correct the gps position.
position interpolation	2 (small improvement)	Arrival of depth and position packets can have a time difference. It is/should be possible to interpolate the position.

Siehe auch

• Bordnetz
• NMEA-Logger_anschliessen