gpsSensor problem with Random Stream

Hi to everybody!

I have a big problem with my gpsSensor. In my model I need to use 2 gps: one for my boat and one for my buoy (target).

The two GPS shares the same characteristics but I expected to have two different random stream. I saw on the decumentation that the deafult RandomStream is Global Stream and it's ok for my sensors, but i would like to have two different random stream for my GPS.

Hope that I weel explained my problem.

Thank you in advance!!!

Answer 1

[Ryan Salvo]

Hi Leonardo,

To set two gpsSensor objects to two independent random streams, you can set the RandomStream and Seed properties on the gpsSensor.

Thanks,

Ryan

% Set each of the seeds to different values. 
seed1 = 20;
seed2 = 40;
gps1 = gpsSensor("RandomStream", "mt19937ar with seed", "Seed", seed1);
gps2 = gpsSensor("RandomStream", "mt19937ar with seed", "Seed", seed2);

[Leonardo Costa]

Thank you Ryan. I've already tried "mt19937ar with seed" but I see only an error in the first step and then a "stepped" signal, just like it is passing throught a Zero roder hold.

[Ryan Salvo]

Hi Leonardo,

Can you share the code use to generate this or create a service request with support to resolve this?

Thanks,

Ryan

[Leonardo Costa]

Sure.

For the other GPS I used the same code with a different Seed number.

Sorry for my Italian-mixed-English inside the script

function output_GPS = fcn(x,RMS)
%% Stato
X = x(1); % FIX
Y = x(2); % FIX
psi = x(3);
u = x(4);
v = x(5);

%% Matrici di rotazione
R_fix_Ned = eul2rotm([pi/2,0,pi]); % Fix To NED Z Y' X''

R_mob_fix = [cos(psi) -sin(psi) 0;... % Mob To Fix
    sin(psi) cos(psi)  0;...
    0            0     1];
%% Coordinate in NED
Pos_Ned = R_fix_Ned*[X;Y;0];
V_Ned = R_fix_Ned*R_mob_fix*[u;v;0];

%% Calcolo posizione in GPS
GPS = gpsSensor('SampleRate',10,...
    'HorizontalPositionAccuracy',RMS,...
    'VelocityAccuracy',0.01,...
    'RandomStream', "mt19937ar with seed",...
    "Seed", 20);


[coord_geo,speed_Ned,~,~] = GPS(Pos_Ned',V_Ned'); % [m],[m/s]

%% Posizione GPS in sistema mobile e fisso
lat = coord_geo(1);
lon = coord_geo(2);
alt = coord_geo(3);
lat0 = 0;
lon0 = 0;
alt0 = 0;

coder.extrinsic('referenceEllipsoid','geodetic2ned')

% % Inizializzazione variabili
fixCoord_GPS = zeros(3,1);
fixSpeed_GPS = zeros(3,1);
mobSpeed_GPS = zeros(3,1);
output_GPS = zeros(4,1);
% %
spheroid = referenceEllipsoid('GRS 80');
[xNorth,yEast,zDown] = geodetic2ned(lat,lon,alt,lat0,lon0,alt0,spheroid);

fixCoord_GPS = R_fix_Ned'*[xNorth;yEast;zDown];

fixSpeed_GPS = R_fix_Ned'*speed_Ned';

mobSpeed_GPS = R_mob_fix'*fixSpeed_GPS;

%% Stato GPS
X_GPS = fixCoord_GPS(1);
Y_GPS = fixCoord_GPS(2);
u_GPS = mobSpeed_GPS(1);
v_GPS = mobSpeed_GPS(2);

output_GPS = [X_GPS;Y_GPS;u_GPS;v_GPS];

end

[Ryan Salvo]

Hi Leonardo,

No problem. The issue is that gpsSensor is getting re-initialized every step in the MATLAB Function Block. Since gpsSensor is a System object, you'll want to make it a persistent variable so that its internal state is maintained between calls to the MATLAB Function Block. Something like this:

function output_GPS = fcn(x,RMS)

% Only create the GPS at the beginning of simulation.
persistent GPS;
if isempty(GPS)
    GPS = gpsSensor('SampleRate',10,...
    'HorizontalPositionAccuracy',RMS,...
    'VelocityAccuracy',0.01,...
    'RandomStream', "mt19937ar with seed",...
    "Seed", 20);
end





%% Stato
X = x(1); % FIX
Y = x(2); % FIX
psi = x(3);
u = x(4);
v = x(5);
%% Matrici di rotazione
R_fix_Ned = eul2rotm([pi/2,0,pi]); % Fix To NED Z Y' X''
R_mob_fix = [cos(psi) -sin(psi) 0;... % Mob To Fix
    sin(psi) cos(psi)  0;...
    0            0     1];
%% Coordinate in NED
Pos_Ned = R_fix_Ned*[X;Y;0];
V_Ned = R_fix_Ned*R_mob_fix*[u;v;0];
%% Calcolo posizione in GPS
[coord_geo,speed_Ned,~,~] = GPS(Pos_Ned',V_Ned'); % [m],[m/s]
%% Posizione GPS in sistema mobile e fisso
lat = coord_geo(1);
lon = coord_geo(2);
alt = coord_geo(3);
lat0 = 0;
lon0 = 0;
alt0 = 0;
coder.extrinsic('referenceEllipsoid','geodetic2ned')
% % Inizializzazione variabili
fixCoord_GPS = zeros(3,1);
fixSpeed_GPS = zeros(3,1);
mobSpeed_GPS = zeros(3,1);
output_GPS = zeros(4,1);
% %
spheroid = referenceEllipsoid('GRS 80');
[xNorth,yEast,zDown] = geodetic2ned(lat,lon,alt,lat0,lon0,alt0,spheroid);
fixCoord_GPS = R_fix_Ned'*[xNorth;yEast;zDown];
fixSpeed_GPS = R_fix_Ned'*speed_Ned';
mobSpeed_GPS = R_mob_fix'*fixSpeed_GPS;
%% Stato GPS
X_GPS = fixCoord_GPS(1);
Y_GPS = fixCoord_GPS(2);
u_GPS = mobSpeed_GPS(1);
v_GPS = mobSpeed_GPS(2);
output_GPS = [X_GPS;Y_GPS;u_GPS;v_GPS];
end

[Leonardo Costa]

Thank you very much!!!