code: private void writeEnvelope(ByteWriter writer) throws IOException {
  
  		if (envelope != null) {
  
  			// Write x and y values
  			writer.writeDouble(envelope.getMinX());
  			writer.writeDouble(envelope.getMaxX());
  			writer.writeDouble(envelope.getMinY());
  			writer.writeDouble(envelope.getMaxY());
  
  			// Write z values
  			if (envelope.hasZ()) {
  				writer.writeDouble(envelope.getMinZ());
  				writer.writeDouble(envelope.getMaxZ());
  			}
  
  			// Write m values
  			if (envelope.hasM()) {
  				writer.writeDouble(envelope.getMinM());
  				writer.writeDouble(envelope.getMaxM());
  			}
  		}
  	}
docs: Write the envelope bytes
  
  @param writer
  byte writer
  @throws IOException