Getting Started

This page walks through the basics of using vnpy in a Python console to connect and read data from a VectorNav sensor.

1. Open a terminal window and execute the command python (Windows) or python3 (Linux).

2. Import all objects from the vnpy namespace:

   >>> from vnpy import *
   

3. Create a new VnSensor object and connect to the sensor, substituting the appropriate connection parameters:

   >>> s = VnSensor()
   >>> s.connect('COM1', 115200)
   

4. Verify connectivity with the sensor by reading the model number:

   >>> s.read_model_number()
   'VN-100T-CR'
   

Note

All methods that read register values from the sensor start with read followed by the register’s name as listed in the sensor’s user manual.

5. Query some orientation data by reading the current values of the Yaw Pitch Roll register:

   >>> s.read_yaw_pitch_roll()
   vec3f([ -43.977, 13.571, 165.119 ])
   

   Individual components of the yaw, pitch, roll can be accessed from the vec3f object.

   >>> ypr = s.read_yaw_pitch_roll()
   >>> ypr.x
   -43.917999267578125
   >>> ypr.y
   13.586000442504883
   >>> ypr.z
   165.1219940185547
   

6. Most registers are accessed using structured objects since their are usually many fields in the register. The previous register was structured using a vec3f object that holds the 3-components of yaw, pitch and roll. More complex register are futher structured depending on the fields present. Let’s see what happens when we query the Yaw, Pitch, Roll, Magnetic, Acceleration, and Angular Rates register:

   >>> reg = s.read_yaw_pitch_roll_magnetic_acceleration_and_angular_rates()
   

You can easily see the structure of the returned object by performing a dir on the object:

>>> dir(reg)
['__class__', '__del__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq_
    _', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__'
    , '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce
    _ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__',
    '__swig_destroy__', '__weakref__', 'accel', 'gyro', 'mag', 'this', 'thisown', 'y
    aw_pitch_roll']

The displayed listing shows a lot of built-in attributes, but at the end, you can see the fields accel, gyro, mag and yaw_pitch_roll. Let’s see what the values for accel are:

>>> reg.accel
vec3f([ 2.247, -2.36, 8.885 ])

7. Let’s do a simple reconfiguration of the sensor to illustrate a write operation. The factory default for asynchronous data output frequency is 40 Hz. You can change this setting to 10 Hz by issuing the commands below.

   >>> s.write_async_data_output_frequency(10)
   >>> s.read_async_data_output_frequency()
   10
   

8. In the previous step, it is possible to send a single value to set the register because the register has a simple arrangement of two fields with the second field being optional. However, many configuration registers have an assortment of many fields. The preferred way to configure these registers is to first read the existing settings, modifying the desired fields in the returned object, and then sending the object to update the register. The commands below illustrate this sequence for the register VPE Basic Control:

   >>> reg = s.read_vpe_basic_control()
   >>> reg.heading_mode
   1
   >>> reg.heading_mode == HEADINGMODE_RELATIVE
   True
   >>> reg.heading_mode = HEADINGMODE_ABSOLUTE
   >>> s.write_vpe_basic_control(reg)
   >>> reg = s.read_vpe_basic_control()
   >>> reg.heading_mode == HEADINGMODE_ABSOLUTE
   True
   

This example also illustrates the use of enums for register fields that only accept a certain range of values.

If you prefer to not do a read of the existing register values followed by modification of only the fields you wish to change, you can also fully specify the fields of the register by creating a new structure with the desired values. The commands below show how to set the register back to its original setting:

>>> reg = VpeBasicControlRegister(VPEENABLE_ENABLE, HEADINGMODE_RELATIVE, VPEMODE_MODE1, VPEMODE_MODE1)
>>> s.write_vpe_basic_control(reg)