TGIS_LayerGML class

DK for Delphi | GisLayerGML.TGIS_LayerGML | Classes | Constructors | Fields | Methods | Properties | Events

Encapsulation of a GML Layer.

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

// Delphi
type
  TGIS_LayerGML = class( TGIS_LayerVector )
  end;

// C++ Builder
class PASCALIMPLEMENTATION TGIS_LayerGML : public TGIS_LayerVector
{
};

→ TGIS_BaseObjectDisposable → TGIS_LayerAbstract → TGIS_Layer → TGIS_LayerVector

Supported shape types:

• Point
• MultiPoint
• Arc
• Polygon
• MultiPatch

To filter a gml file based on a feature layer and shape type, additional parameters must be added to the layer Name property in format : “Name;sublayer_name;shape_type_wkt” :

lv.Name = "Objects;buildings;POLYGON"

before opening a layer.

The GetAvailableLayers function can be used to obtain a list of available layers with their shape type and features count.

Available metadata keys:

The layer axis order forced to be revered by:

• changing AxisOrderReversed property
• use Metadata TGIS_LayerGML.AxisOrderReversed=true

The layer reads CityGML geometry as MultiPatch shapes.

By default, a CityGML feature containing many nested geometries or mixed LODs is represented by a shape with many parts. Setting TGIS_LayerGML.CityGMLSplitFeatures metadata to true allows splitting each feature by type and LOD level into separate shapes. The feature will be described by extra fields: CITYGML_LOD and CITYGML_TYPE, which can be used to filter or render visible shapes.

Some gml files have very complex schema and the parser may not detect shape attributes correctly due to unrecognized features declaration. To solve such issues, a .xsd file can be created (with the same name as gml file) with xsd:element declaration defining a feature name that will be recognized and start collecting attributes.

A sample schema file (name attribute must be changed) :

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:gml="http://www.opengis.net/gml" xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" version="1.0">
    <xsd:import namespace="http://www.opengis.net/gml" schemaLocation="feature.xsd"/>
    <xsd:element name="product_LVC:LVC-product" type="FeatureCollection" substitutionGroup="gml:_FeatureCollection"/>
    <xsd:element name="bag_LVC:Pand" type="Feature" substitutionGroup="gml:_Feature"/>
    <xsd:complexType name="FeatureCollection">
        <xsd:complexContent>
            <xsd:extension base="gml:AbstractFeatureCollectionType"/>
        </xsd:complexContent>
    </xsd:complexType>
    <xsd:complexType name="Feature">
        <xsd:complexContent>
            <xsd:extension base="gml:AbstractFeatureType">
                <xsd:sequence>
                    <xsd:element name="bag_LVC:pandGeometrie" type="gml:GeometryPropertyType" nillable="true" minOccurs="1" maxOccurs="1" />
                </xsd:sequence>
            </xsd:extension>
        </xsd:complexContent>
    </xsd:complexType>
</xsd:schema>

The layer will also recognize xsi:schemaLocation in .xml file and try to parse a local schema file.