Developer's Guide - MapGuide Open Source - OSGeo

Measuring Distance
Measuring distance in geographic or projected coordinate systems requires
great circle calculations. Both MgGeometry::Buffer() and
MgGeometry::Distance() accept a measurement parameter that defines the
great circle to be used. If the measurement parameter is null, the calculation
is done using a linear algorithm.
Create the measurement parameter, an MgCoordinateSystemMeasure object,
from the MgCoordinateSystem object.
Distance is calculated in the units of the SRS. MgCoordinateSystem includes
two methods, ConvertCoordinateSystemUnitsToMeters() and
ConvertMetersToCoordinateSystemUnits() to convert to and from linear
distances.
For example, to calculate the distance between two MgGeometry objects $a and
$b, using the coordinate system $srs, perform the following steps:
$measure = new MgCoordinateSystemMeasure($srs);
$distInMapUnits = $a->Distance($b, $measure);
$distInMeters = $srs->ConvertCoordinateSystemUnitsToMeters(
$distInMapUnits);
Another way to calculate the distance is to use
MgCoordinateSystemMeasure::GetDistance(), as in the following:
$distInMapUnits = $measure->GetDistance($a, $b);
Temporary Feature Sources
Many geometric analysis operations require creating new features and new
feature sources. For example, drawing a buffer around a point on a map requires
a layer to display the buffer polygon, and the layer requires a feature source.
To create a temporary feature source, perform the following steps:
■ Create a feature class definition.
■ Determine what properties you need to store for the features. Add the
property definitions to the feature class definition.
■ Create a feature schema containing the feature class definition.
76 | Chapter 5 Analyzing Features