TGIS_LayerWFS class

DK11 for .NET | TatukGIS.NDK.TGIS_LayerWFS | Classes | Constructors | Fields | Methods | Properties

Encapsulation of an OpenGIS WFS layer.

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

// C#
public class TGIS_LayerWFS : TGIS_LayerCompoundVector
{
}

' VisualBasic
Public Class TGIS_LayerWFS
  Inherits TGIS_LayerCompoundVector
End Class

// Oxygene
type
  TGIS_LayerWFS = public class( TGIS_LayerCompoundVector )
  end;

→ TGIS_BaseObjectDisposable → TGIS_LayerAbstract → TGIS_Layer → TGIS_LayerCompoundAbstract → TGIS_LayerCompoundVector

To open a layer, provide the path with the GetCapabilities request like:

 Layer.Path := ‘http://WFS.jpl.nasa.gov/WFS.cgi?SERVICE=WFS&REQUEST=GetCapabilities’ ;

This layer can also be opened by opening the file name_of_layer.ttkwp or embedding all parameters to the Path property as CRLF or '\n' delimited string. The structure of this file must be:

  [TatukGIS Layer]
  Storage=WFS
  Name=layer name
  Caption=layer caption
  Url=wfs server url
  .....
  AxisOrder=NE or EN (default) (obsolete)
  AxisOrderReversed=reverse coordinates of axis for some coordinate systems
  AxisOrderIgnored=ignore axis order from the coordinate system (only for 1.1.0 services or higher)
  ExtentOrder=set XX or XY to define how a bounding box of a layer is defined
  PagingEnabled=True|False request data in pages (default false)
  PageSize=number of features per page (default 1000)
  UserAgent=user agent
  TimeOut=connection timeout (default 90000)

If the GetCapabilities is omitted then the class will try to recognize the server of its own:

  Layer.Path := 'http://WFS.jpl.nasa.gov/WFS.cgi?SERVICE=WFS' ;

It is possible to embed into Path additional WFS parameters like VERSION, TYPENAME, SRSNAME, OUTPUTFORMAT, MAXFEATURES, STARTINDEX, BBOX, CQL_FILTER, AxisOrderIgnored, AxoisOrderReversed, ExtentOrder, PAGINGENABLED or PAGESIZE like

  layer.Path := 'http://WFS.jpl.nasa.gov/WFS.cgi?SERVICE=WFS&FORMAT=image/jpeg&LAYERS=global_mosaic' ;

These parameters must be embedded into the URL, not as extra lines in the .ttkwp file.

For WFS servers that require authentication, it is possible to embed into Path additional parameters USER, PASS like

  layer.Path := 'http://WFS.jpl.nasa.gov/WFS.cgi?SERVICE=WFS&USER=test&PASS=test' ;

or use templates format instead of real parameter values and OnPassword event for secured decoding like

  layer.Path := 'http://WFS.jpl.nasa.gov/WFS.cgi?SERVICE=WFS&USER=<#USER#>&PASS=<#PASS#>' ;

The layer should properly recognize axis order. However, the axis order can be modified to:

• force reversed axis order use AxisOrderReversed=true definition and:
  • embed into a URL
  • store in a .ttkwp file
  • store in a layer configuration file or project file
  • use Metadata TGIS_LayerWFS.AxisOrderReversed=true
• ignore axis order recognition use AxisOrderIgnored=true definition and:
  • embed into a URL
  • store in a .ttkwp file
  • store in a layer configuration file or project file
  • use Metadata TGIS_LayerWFS.AxisOrderIgnored=true

For big datasets, users can enable Paging which allows reading the data in chunks defined by page size. This is a preferred solution to avoid timeouts from a server. The Paging can be enabled by adding PagingEnabled and PageSize to a URL, .ttkwp file, or using Metadata TGIS_LayerWFS.PagingEnabled and TGIS_LayerWFS.PageSize.

The TimeOut can be enabled by adding TimeOut to a URL, .ttkwp file, or using Metadata TGIS_LayerWFS.TimeOut.

To avoid blocking a layer during the opening of a project, after the initial setup a layer is empty. The data is fetched upon calling Draw on the layer.

By default, sublayers are empty after opening a layer and filled upon drawing. To get field structure just after opening a layer (adding to the viewer), Metadata TGIS_LayerWFS.QueryStructureMode can be set with the value:

• 0 - no structure query, call Draw() instead to read fields
• 1 - use DescribeFeatureType request to get XML schema and read fields
• 2 - fetch a feature to read fields

• When using some https servers, to solve the WebException error “Could not create SSL/TLS secure channel” the default security protocol using ServicePointManager.SecurityProtocol must be changed in the user application:

  ServicePointManager.SecurityProtocol = 
     SecurityProtocolType.Tls   | 
     SecurityProtocolType.Tls11 | 
     SecurityProtocolType.Tls12 | 
     SecurityProtocolType.Ssl3  ;

  This is a .NET Framework restriction.