function(feature) {
		if (!(feature in this.featureNameToFeatureIndex)) {
			var newIndex = this.featureIndexToFeatureName.length;
			this.featureIndexToFeatureName.push(feature);
			this.featureNameToFeatureIndex[feature] = newIndex;
		}
	}
function(feature) {
		if (!(feature in this.featureNameToFeatureIndex)) {
			var newIndex = this.featureIndexToFeatureName.length;
			this.featureIndexToFeatureName.push(feature);
			this.featureNameToFeatureIndex[feature] = newIndex;
		}
	}
function ( feature ) { if ( ! ( feature in this . featureNameToFeatureIndex ) ) { var newIndex = this . featureIndexToFeatureName . length ; this . featureIndexToFeatureName . push ( feature ) ; this . featureNameToFeatureIndex [ feature ] = newIndex ; } }
add a single feature, if it does not exist
add a single feature if it does not exist