if not ('z2' in sourceNames): outputFields.append(QgsField('z2', QVariant.Double))
if not ('Length' in sourceNames): outputFields.append(QgsField('Length', QVariant.Double))
if not ('LineString' in sourceNames): outputFields.append(QgsField('LineString', QVariant.String))
if not ('z2' in sourceNames): outputFields.append(QgsField('z2', QVariant.Double))
if not ('Length' in sourceNames): outputFields.append(QgsField('Length', QVariant.Double))
if not ('LineString' in sourceNames): outputFields.append(QgsField('LineString', QVariant.String))