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<concept id="GUID-AD7D9D39-6FF0-5811-9708-98538271BA0D" xml:lang="en"><title>Position
data</title><shortdesc>This document describes the basic and extended classes that hold
position data. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section><title>Purpose</title> <p>This document describes how position data
is represented within the <xref href="GUID-ABC01315-D65D-55EA-9D42-4DE6384D517D.dita">position
data classes</xref>. </p> </section>
<section><title>Values and co-ordinates</title> <ul>
<li id="GUID-23C5B7B1-8F7E-5E67-BFC5-8B6ADF2EC263"><p>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 &lt;= Lat &lt;= +90) and longitude values have the range (-180
&lt;= Long &lt; +180). </p> </li>
<li id="GUID-3F2BFE0F-29A1-516D-A27B-35298AD35FC8"><p>In LBS, latitude and
longitude are held as <codeph>TReal64</codeph> values and altitude is held
as a <codeph>TReal32</codeph> value. </p> </li>
<li id="GUID-EB9BEB2B-2CC2-5C70-9A88-4C9D80F42D0A"><p>Both horizontal and
vertical accuracy are held as <codeph>TReal32</codeph> values and represent
a possible error values in metres. </p> </li>
<li id="GUID-9909202F-8C8C-5EAA-814F-B9760CE63F6C"><p>Bearings and headings
are held as <codeph>TReal32</codeph> values and represent a direction in degrees.
Bearing and heading accuracies are also held as <codeph>TReal32</codeph> values
and represent a possible error value in degrees. </p> </li>
</ul> </section>
<section><title>Co-ordinate adjustment</title> <p>The <xref href="GUID-DDCBA817-9D88-3332-ABD3-1DDC6E397851.dita"><apiname>TCoordinate</apiname></xref> 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 <codeph>TCoordinate</codeph> class then the values
are adjusted to lie within the correct interval. </p> </section>
<section><title>Unassigned values</title> <p>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 <xref href="GUID-1DB7AE7A-A505-3530-AC2B-EBAEFCD3F36A.dita#GUID-1DB7AE7A-A505-3530-AC2B-EBAEFCD3F36A/GUID-79B7EC5D-973E-3B91-91C4-48F10FC0038D"><apiname>Math::IsNaN()</apiname></xref> on
each returned co-ordinate value before using it in a calculation. </p> </section>
</conbody><related-links>
<link href="GUID-70E1117B-17F0-5CF4-A5D0-35D3BEBB0FEA.dita"><linktext>Position
Area Data Classes</linktext></link>
<link href="GUID-ACD9E338-DF75-5811-B696-C3900B498218.dita"><linktext>Privacy Requester
Classes</linktext></link>
</related-links></concept>