scripting/scripting.m

The example Getting Started show some simple methods for accessing a VectorNav sensor from the Command Window. However, these methods are not very suited for creating self-contained scripts. This example shows the previous shortcomings and how to create proper scripts that access VectorNav sensors.

Note

This example was constructed using Mathworks MATLAB R2014b and may need to be adjusted for your specific version.

Steps

1. Open MATLAB. Now open the script located at <root>/matlab/examples/scripting/scripting.m.
   
   
2. Modify the variables at the top for your system and save.
   
   
3. Execute the script.
   
   
4. Review the script comments for explanation of the code.

% Update for your system.
VnDotNetAssemblyPath = 'C:\vnproglib\net\bin\win32\VectorNav.dll';
SensorComPort = 'COM1';
SensorBaudrate = 115200;

NET.addAssembly(VnDotNetAssemblyPath);

% The getting_started example showed some basics of using the VectorNav
% .NET Library within MATLAB from the Command Window. However, some of
% these methods are not particularly suited for creating scripts. This
% example will demonstrate these short coming in suggest better methods for
% script generation.

% First, it is tedious to type the fully qualified names for objects. For
% example, to connect to a sensor, the following command was used...
%
% >> ez = VectorNav.Sensor.EzAsyncData.Connect('COM1', 115200);
%
% Let's get rid of the namespace qualifications to make the code a little
% clearer.
import VectorNav.Sensor.*;
import VectorNav.Protocol.Uart.*;

% Now to connect to the sensor, we can use the short hand. Be sure to
% change the connection parameters for your setup.
ez = EzAsyncData.Connect(SensorComPort, SensorBaudrate);

% Let's configure the sensor out output yaw, pitch, roll data at 2 Hz.
ez.Sensor.WriteAsyncDataOutputType(AsciiAsync.VNYPR);
ez.Sensor.WriteAsyncDataOutputFrequency(2);

% Now suppose we wish to receive and process the data packets that are
% received. Using the methods in getting_started, this involved accessing
% the ez.CurrentData property. If this method is used in scripting, the
% results are probably what we desire.

% More info on this 'pause' below.
pause(1);

fprintf('Calling ez.CurrentData\n');
for n = 1:10
    cd = ez.CurrentData;
    fprintf('YPR: %3.2f %3.2f %3.2f\n', cd.YawPitchRoll.X, cd.YawPitchRoll.Y, cd.YawPitchRoll. Z);
end

% Now instead of displaying each new data packet received, our for loop
% just zipped on through as fast as it could displaying the 'current data'.
% For scripting, the preferred choice is to call GetNextData since this
% will block the script until a new data packet is received. Also, the
% pause function was used because since the script is running much faster
% than data can be received on the serial port and processed, we are very
% likely to get a "Nullable object must have a value" error. This is
% because our script create the EzAsyncData object and tried reading data
% before it has any data from the sensor.

fprintf('Calling ez.GetNextData()\n');
for n = 1:10
    cd = ez.GetNextData();
    fprintf('YPR: %3.2f %3.2f %3.2f\n', cd.YawPitchRoll.X, cd.YawPitchRoll.Y, cd.YawPitchRoll. Z);
end

% Depending on the complexity of your script, you may not wish to wait
% forever for the next available data. In this case, you can specify a
% timeout value call to GetNextData. When you do this, you must check to
% see if the returned data is null or not.

fprintf('Calling ez.GetNextData() with timeout\n');
for n = 1:10
    cd = ez.GetNextData(250);
    
    if isempty(cd)
        fprintf('No data available.\n')
    else
        fprintf('YPR: %3.2f %3.2f %3.2f\n', cd.YawPitchRoll.X, cd.YawPitchRoll.Y, cd.YawPitchRoll. Z);
    end
end

ez.Disconnect();