Returns the coordinate z of a point. This function only can be used in Informix and Postgres. In addition, it is required that the geometric objects to which it applias are of POINT type. So, it cannot be applied directly to the points stored in columns of geometric type.
 

1 geo.getZ

<geo.getZ>
    <geom_column /> *
</geo.getZ>
Example
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<select>
    <columns>
        <geo.getZ>a.the_geom</geo.getZ>
    </columns>
    <from table='points' alias='a' />
</select>