Data standards for e-Logbooks

Geographical Coordinates

Purpose

To provide a standard for the storage and use of geographical data.

Introduction

Geographical coordinates will use latitude and longitude in the following formats:

Latitude

Latitude is represented in degrees, minutes and seconds.

Degrees range from 0 (equator) to 90 (north or south of the equator), minutes and seconds have a range from 0 to 60. Latitude must also be qualified as to whether the position is in the northern (N) or the southern hemisphere (S). The convention will be to use S or N to indicate the hemisphere. Alternatively, latitude can be described in decimal degrees where a “+” sign will be used for latitudes north of the equator and a “–“ sign for latitudes south of the equator. Decimal degrees of latitude range from –90 to +90.

Longitude

Longitude is represented in degrees, minutes and seconds.

Degrees range from 0 (Greenwich – UK) to 180 (east or west of Greenwich), minutes and seconds range from 0 to 60. Longitude must also be qualified as to whether the position is east (E) or west (W) of Greenwich. The convention will be to use E or W to indicate the hemisphere.

Alternatively, longitude can be described in decimal degrees a “+” sign will be used for longitudes east of the Greenwich and “–“ sign for longitudes west of Greenwich.

Precision of coordinates

The use of seconds is only required where a high level of precision is needed. Limiting geographical coordinates to degrees and minutes provides a resolution of approximately 1 nautical mile (1.852 km). Using seconds in coordinates will increase the resolution of the position to 1/60 nautical miles (around 30 m). Where positional coordinates are represented in decimal degrees, five (5) decimal places will be required to give a resolution of approximately 1 m.

Examples of acceptable formats
Latitude
Longitude
Format Example Format Example
Degrees and minutes dd mm N/S 43 30’ S ddd mm E/W 145 30 E
Decimal degrees -dd.ddddd -43.50000 -ddd.ddddd +145.50000
Degrees and decimal minutes dd mm.mm N/S 43 30.00 ddd mm.mm E/W 145 30.00 E
Degrees, minutes, seconds dd mm ss N/S 43 30’ 00” S ddd mm ss E/W 145 30’ 00” E

Datum

AFMA has adopted the Geocentric Datum Australia (GDA) as the datum to reference geographical coordinates. The GDA and the WGS84 (used in GPS system) are almost synonymous for practical purposes in fisheries applications (difference being around 10cm).