TGIS_IsochroneMap class

DK11 for .NET | TatukGIS.NDK.TGIS_IsochroneMap | Classes | Constructors | Methods | Properties

Network analysis tool for creating isochrone maps - for a given point finds the network area reachable within a given maximum network traversing cost.

Available also on: Delphi | Java | ActiveX | Python.

// C#
public class TGIS_IsochroneMap : TGIS_BaseObjectDisposable
{
}

' VisualBasic
Public Class TGIS_IsochroneMap
  Inherits TGIS_BaseObjectDisposable
End Class

// Oxygene
type
  TGIS_IsochroneMap = public class( TGIS_BaseObjectDisposable )
  end;

→ TGIS_BaseObjectDisposable

For general information about isochrone maps see this article on Wikipedia.

TGIS_IsochroneMap uses topological network (TGIS_Network) for calculations (the same as TGIS_ShortestPath). If the network is not available for the analyzed layer then it will be created automatically. Depending on the size of the layer it may be a prolonged operation. Once created the network is saved into a set of files and can be reused.

The creation of an isochrone map can also be a time consuming operation for large and complicated networks and/or relatively big traversing cost.

Sample results from isochrone analyses:

Points	Arcs	Polygons	Interpolation (splines)

Steps to achieve:

• Points
  1. Use Generate() with TGIS_ShapePoint as the output type
  2. Colorize the layer by the cost field (GIS_COST by default)
• Arcs
  1. Use Generate() with TGIS_ShapeArc as the output type
  2. Colorize the layer by the cost field (GIS_COST by default)
• Polygons
  1. Use Generate() with TGIS_ShapePolygon as the output type
  2. Repeat above desired number of times decreasing the cost each time
  3. Colorize the layer by the cost field (GIS_COST by default)
• Interpolation
  1. Use Generate() with TGIS_ShapePoint as an output type
  2. Use TGIS_InterpolationSplines to generate interpolated grid layer
  3. Colorize the grid layer

// GIS is TGIS_ViewerWnd
 
// simple LinkCostEvent handler which uses shape length as the network cost
private void doLinkCostEvent( Object _sender, TGIS_LinkCostEventArgs _e )
{
  if( _e.Shape.Layer.CS is TGIS_CSUnknownCoordinateSystem )
  {
    _e.Cost = _e.Shape.Length() ;
  }
  else
  {
    _e.Cost = _e.Shape.LengthCS() ;
  }
  _e.RevCost = _e.Cost ;
}
 
public void MakeIsochroneMap( TGIS_Point _pt )
{
  // get a layer for which an isochrone map will be created
  TGIS_LayerVector ls = (TGIS_LayerVector)GIS.Get( "Roads" ) ;
 
  // create a layer to store the isochrone map on
  TGIS_LayerVector lr = new TGIS_LayerVector() ;
  lr.Name = "Isochrone map for Roads" ;
  lr.CS = ls.CS ;
  lr.Open() ;
 
  // maximum traversing cost for the isochrone map
  double cst = 10.0 ;  
 
  TGIS_ShortestPath sp = new TGIS_ShortestPath( GIS ) ;
  sp.LinkCostEvent += doLinkCostEvent ;
 
  TGIS_IsochroneMap im = new TGIS_IsochroneMap( GIS ) ;
  // generate the isochrone map
  im.Generate( ls, sp, lr, TGIS_ShapeType.Arc, _pt, cst, 0 ) ;
 
  // add the layer with the isochrone map to the viewer
  GIS.Add( lr ) ;  
  // and update
  GIS.InvalidateWholeMap() ;
}

• IsochroneMap sample