Set start position of experiment to position of first field.

def update_start_position(self):
        "Set start position of experiment to position of first field."
        x_start = self.field_array.ScanFieldData.FieldXCoordinate
        y_start = self.field_array.ScanFieldData.FieldYCoordinate

        # empty template have all fields positions set to zero
        # --> avoid overwriting start position
        if x_start != 0 and y_start != 0:
            self.properties.ScanFieldStageStartPositionX = int(x_start * 1e6) # in um
            self.properties.ScanFieldStageStartPositionY = int(y_start * 1e6)