Position -data

Position -dataThis document describes the basic and extended classes that hold -position data. -

Purpose

This document describes how position data -is represented within the position -data classes.

Values and co-ordinates

The World Geodetic System -reference datum (WGS 84) is used by LBS. This is a global co-ordinate system -in which co-ordinates are expressed as latitude and longitude in degrees and -altitude in metres above the reference datum. In WGS 84, latitude values have -the range (-90 <= Lat <= +90) and longitude values have the range (-180 -<= Long < +180).
In LBS, latitude and -longitude are held as TReal64 values and altitude is held -as a TReal32 value.
Both horizontal and -vertical accuracy are held as TReal32 values and represent -a possible error values in metres.
Bearings and headings -are held as TReal32 values and represent a direction in degrees. -Bearing and heading accuracies are also held as TReal32 values -and represent a possible error value in degrees.

Co-ordinate adjustment

The TCoordinate base -class holds the latitude, longitude and altitude of a position. If an application -attempts to assign values that are outside of the ranges specified by WGS -84 to an instance of a TCoordinate class then the values -are adjusted to lie within the correct interval.

Unassigned values

In some situations, one of the -position co-ordinates, typically altitude may not be known. This is usually -because the positioning module that was used to obtain the location fix was -unable to obtain data for that co-ordinate. Where LBS cannot assign a value -to a co-ordinate value, the value "Not a Number" (NaN) is assigned to it. -Applications must test for this situation by calling Math::IsNaN() on -each returned co-ordinate value before using it in a calculation.

-Position -Area Data Classes -Privacy Requester -Classes + + + + + +Position +dataThis document describes the basic and extended classes that hold +position data. +

Purpose

This document describes how position data +is represented within the position +data classes.

Values and co-ordinates

The World Geodetic System +reference datum (WGS 84) is used by LBS. This is a global co-ordinate system +in which co-ordinates are expressed as latitude and longitude in degrees and +altitude in metres above the reference datum. In WGS 84, latitude values have +the range (-90 <= Lat <= +90) and longitude values have the range (-180 +<= Long < +180).
In LBS, latitude and +longitude are held as TReal64 values and altitude is held +as a TReal32 value.
Both horizontal and +vertical accuracy are held as TReal32 values and represent +a possible error values in metres.
Bearings and headings +are held as TReal32 values and represent a direction in degrees. +Bearing and heading accuracies are also held as TReal32 values +and represent a possible error value in degrees.

Co-ordinate adjustment

The TCoordinate base +class holds the latitude, longitude and altitude of a position. If an application +attempts to assign values that are outside of the ranges specified by WGS +84 to an instance of a TCoordinate class then the values +are adjusted to lie within the correct interval.

Unassigned values

In some situations, one of the +position co-ordinates, typically altitude may not be known. This is usually +because the positioning module that was used to obtain the location fix was +unable to obtain data for that co-ordinate. Where LBS cannot assign a value +to a co-ordinate value, the value "Not a Number" (NaN) is assigned to it. +Applications must test for this situation by calling Math::IsNaN() on +each returned co-ordinate value before using it in a calculation.

+Position +Area Data Classes +Privacy Requester +Classes

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