How to segment the streamslice image of GGVF?

Plot the figure from the vector data with streamslice function of it, now I have tried the trajectory of streamslice figure but could not get any result of it.

figure;
[x_grid,y_grid] = meshgrid(1:ny,1:nx);
hold on;
v = quiver(x_grid,-y_grid,-iggvfnx,iggvfny,'ShowArrowHead','off','Color','c','LineStyle','-','LineWidth',1,'Alignment','center');
hold on;
s_slice = streamslice(x_grid,-y_grid,[],-iggvfnx,iggvfny,[],[],[],1,10,"noarrows","cubic");
set(s_slice,'LineWidth',0.2)
set(s_slice,'Color','b');

Plotted the figure from the vector data with streamslice of it, now I have tried the trajectory of streamslice figure as :

figure;
s_slice = streamslice(x_grid,-y_grid,[],-iggvfnx,iggvfny,[],[],[],1,10,"noarrows","cubic");
hold on;
N_trajects = length(s_slice); % the number of all trajectories
n = 3; % the chosen trajectory
hold on;
C = contourf(x_grid, -y_grid, iggvfnx+iggvfny, n);  
colormap("hot");

[KSSV]

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