gpsSensor problem with Random Stream
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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!!!
采纳的回答
Ryan Salvo
2021-4-28
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);
5 个评论
Leonardo Costa
2021-4-28
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
2021-4-28
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
2021-4-28
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
2021-4-28
编辑：Ryan Salvo
2021-4-28
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
2021-4-29
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