Pitney Bowes MapXtreme - Manual (Page 375)

Chapter 20: Routing
Iso Routing (Drive-Time and Drive-Distance)
MapXtreme v7.1 382 Developer Guide
Creating an IsoDistance (Drive-Distance)
When creating an isoDistance, you are looking for one or more polygons/set of nodes which
represent the area that can be travelled along a road network, given a distance (drive-distance cost)
from a starting location.
The cost specified for an isoDistance request is similar to an isoChrone except the cost value is a
measure of distance used to calculate the isogram. The cost represents the distance required to
travel from the starting point to the calculated points on the road network. You can specify multiple
costs to produce concentric bands (multiple isoDistances) that visually represent different distances
that can be reached along the road network. Associated with multiple costs are tags. You can
specify a tag, or ID, for each cost in the request, that will identify the appropriate iso result
(geometry) in the response.
The following code sample shows how to define an IsoDistanceDefinition. The response will create
an isogram (geometry) using the point as the center and a cost in miles (pt,
DistanceUnit.Mile) defining the boundary:
Public Shared Sub New_IsoDistanceDefinition()
’ Create a point
Dim coordSys As MapInfo.Geometry.CoordSys = _
Session.Current.CoordSysFactory.CreateFromPrjString("1, 104")
Dim dpt As MapInfo.Geometry.DPoint = _
New MapInfo.Geometry.DPoint(-74, 42)
Dim pt As MapInfo.Geometry.Point = _
New MapInfo.Geometry.Point(coordSys, dpt)
’ Create a definition
Dim def As IsoDistanceDefinition = _
New IsoDistanceDefinition(pt, DistanceUnit.Mile)
End Sub
There are numerous preferences you can specify in the IsoDistancePreferences and
IsogramPreferences Classes. These preferences allow you to obtain a desired output for your
analysis. The preferences specified in the IsogramPreferences Class are the same for both an
isoDistance and isoChrone request. For a description of the IsogramPreferences, refer to
IsogramPreferences .
IsoDistancePreferences
The following preferences are available in the IsoDistancePreferences Class:
• DefaultPropagationFactor - Determines the off-road network percentage of the remaining cost
(distance) for which off network travel is allowed when finding the isoDistance boundary. Roads
not identified in the network can be driveways or access roads, among others. The propagation
factor is a percentage of the cost used to calculate the distance between the starting point and
the isoDistance. For example, if you were at a point with five miles left to go on an isoDistance on
the off-road network, boundary points would be put at a distance based on the propagation factor
and the distance left. So, if the propagation factor was 0.16, boundary points would be put at a
distance of 0.8 miles.
• PropagationFactorOverrides - Overrides the propagation factor for a specific road type. The
propagation factor can be overridden for all road types. For example, it may be set to 0.24 for
major urban roads: