AsGML
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## Name

AsGML — Returns the GML representation of a topogeometry.

## Synopsis

`text AsGML(`topogeometry tg`)`;

`text AsGML(`topogeometry tg, text nsprefix_in`)`;

`text AsGML(`topogeometry tg, regclass visitedTable`)`;

`text AsGML(`topogeometry tg, regclass visitedTable, text nsprefix`)`;

`text AsGML(`topogeometry tg, text nsprefix_in, integer precision, integer options`)`;

`text AsGML(`topogeometry tg, text nsprefix_in, integer precision, integer options, regclass visitedTable`)`;

`text AsGML(`topogeometry tg, text nsprefix_in, integer precision, integer options, regclass visitedTable, text idprefix`)`;

`text AsGML(`topogeometry tg, text nsprefix_in, integer precision, integer options, regclass visitedTable, text idprefix, int gmlversion`)`;

## Description

Returns the GML representation of a topogeometry in version GML3 format. If no `nsprefix_in` is specified then `gml` is used. Pass in an empty string for nsprefix to get a non-qualified name space. The precision (default: 15) and options (default 1) parameters, if given, are passed untouched to the underlying call to ST_AsGML.

The `visitedTable` parameter, if given, is used for keeping track of the visited Node and Edge elements so to use cross-references (xlink:xref) rather than duplicating definitions. The table is expected to have (at least) two integer fields: 'element_type' and 'element_id'. The calling user must have both read and write privileges on the given table. For best performance, an index should be defined on `element_type` and `element_id`, in that order. Such index would be created automatically by adding a unique constraint to the fields. Example:

    CREATE TABLE visited (
      element_type integer, element_id integer,
      unique(element_type, element_id)
    );

The `idprefix` parameter, if given, will be prepended to Edge and Node tag identifiers.

The `gmlver` parameter, if given, will be passed to the underlying ST_AsGML. Defaults to 3.

Availability: 2.0.0

## Examples

This uses the topo geometry we created in CreateTopoGeom

    SELECT topology.AsGML(topo) As rdgml
      FROM ri.roads
      WHERE road_name = 'Unknown';

    -- rdgml--
    <gml:TopoCurve>
        <gml:directedEdge>
            <gml:Edge gml:id="E1">
                <gml:directedNode orientation="-">
                    <gml:Node gml:id="N1"/>
                </gml:directedNode>
                <gml:directedNode></gml:directedNode>
                <gml:curveProperty>
                    <gml:Curve srsName="urn:ogc:def:crs:EPSG::3438">
                        <gml:segments>
                            <gml:LineStringSegment>
                                <gml:posList srsDimension="2">384744 236928 384750 236923 384769 236911 384799 236895 384811 236890
                                384833 236884 384844 236882 384866 236881 384879 236883 384954 236898 385087 236932 385117 236938
                                385167 236938 385203 236941 385224 236946 385233 236950 385241 236956 385254 236971
                                385260 236979 385268 236999 385273 237018 385273 237037 385271 237047 385267 237057 385225 237125
                                385210 237144 385192 237161 385167 237192 385162 237202 385159 237214 385159 237227 385162 237241
                                385166 237256 385196 237324 385209 237345 385234 237375 385237 237383 385238 237399 385236 237407
                                385227 237419 385213 237430 385193 237439 385174 237451 385170 237455 385169 237460 385171 237475
                                385181 237503 385190 237521 385200 237533 385206 237538 385213 237541 385221 237542 385235 237540 385242 237541
                                385249 237544 385260 237555 385270 237570 385289 237584 385292 237589 385291 237596 385284 237630</gml:posList>
                            </gml:LineStringSegment>
                        </gml:segments>
                    </gml:Curve>
                </gml:curveProperty>
            </gml:Edge>
        </gml:directedEdge>
    </gml:TopoCurve>

Same exercise as previous without namespace

    SELECT topology.AsGML(topo,'') As rdgml
      FROM ri.roads
      WHERE road_name = 'Unknown';

    -- rdgml--
    <TopoCurve>
        <directedEdge>
            <Edge id="E1">
                <directedNode orientation="-">
                    <Node id="N1"/>
                </directedNode>
                <directedNode></directedNode>
                <curveProperty>
                    <Curve srsName="urn:ogc:def:crs:EPSG::3438">
                        <segments>
                            <LineStringSegment>
                                <posList srsDimension="2">384744 236928 384750 236923 384769 236911 384799 236895 384811 236890
                                384833 236884 384844 236882 384866 236881 384879 236883 384954 236898 385087 236932 385117 236938
                                385167 236938 385203 236941 385224 236946 385233 236950 385241 236956 385254 236971
                                385260 236979 385268 236999 385273 237018 385273 237037 385271 237047 385267 237057 385225 237125
                                385210 237144 385192 237161 385167 237192 385162 237202 385159 237214 385159 237227 385162 237241
                                385166 237256 385196 237324 385209 237345 385234 237375 385237 237383 385238 237399 385236 237407
                                385227 237419 385213 237430 385193 237439 385174 237451 385170 237455 385169 237460 385171 237475
                                385181 237503 385190 237521 385200 237533 385206 237538 385213 237541 385221 237542 385235 237540 385242 237541
                                385249 237544 385260 237555 385270 237570 385289 237584 385292 237589 385291 237596 385284 237630</posList>
                             </LineStringSegment>
                        </segments>
                    </Curve>
                </curveProperty>
            </Edge>
        </directedEdge>
    </TopoCurve>

## See Also

CreateTopoGeom, ST_CreateTopoGeo

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