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Mapping Segmented Geometric Information

Sometimes it may take more than one mapping rule to successfully extract the geometric data from the elements in the input XML document stream. Consider the following polyline element:

<polyline>
	<coord>0.0,0.0</coord>
	<coord>1.1,2.2</coord>
	<coord>5.3,-1.9</coord>
	<coord>7.9,3.5</coord>
</polyline>

Refer to FME Feature Construction (defining mapping rules under the <feature-content-map> element). It explains when mapping rules should be define under the <feature-content-map> element to handle cases like this one.

What we need here is to activate just one geometry builder B – one that constructs a line geometry. If we just define one feature mapping rule matching the <polyline> element, then we will not be able to give B the contents of all the <coord> elements because B gets suspended when the <polyline> element ceases to be the context element.

Recall that a suspended geometry builder may be set to the state of execution if the currently executing mapping rule contains a <geometry> element having no activate attribute.

We need to re-execute B and pass it the contents of the <coord> element when this element is matched. To achieve, this we define an additional feature mapping rule, that matches a <coord> element and contains a <geometry> element with no activate attribute.

The following xfMap document fragment does exactly this. The built-in geometry builder xml-line constructs polyline features.

<feature-map>
	<mapping match="polyline">
		 ... 
		<geometry activate="xml-line">
	</geometry>
	</mapping>
</feature-map>

<feature-content-map>
	<mapping match="coord">
	...
	<geometry>
		<!-- activate attribute missing, execute
			the suspended mapping rule passing it 
			the parameters that are defined in the 
			geometry.
						
			NOTE: It is an error to define a mapping rule
			of this form if no geometry builder was
			activated. -->
	
		<data name=”data-string”>
			<extract expr=”.”/>
		</data>
	</geometry>

	</mapping>
</feature-content-map>