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Hi, you can add a Filter subnode to the Particle Trajectories plot type. You can only render a certain number or fraction of all the particles. In addition, you can also use a logical expression to pick out specific particles. Each particle is assigned a unique number, determined by the variable fpt.pidx (if fpt is the identifier for the Particle Tracing for Fluid Flow interface). You could use a logical expression like fpt.pidx==100 to only render the particle whose index is 100.

for the logical expression, we can just input logical number? can we try initial position?

for the logical expression, we can just input logical number? can we try initial position?

To use initial position, just use the at() operator. So, to look at the particles whose initial x-position is greater than 0 you would type at(0,qx>0) into the "Logical expression for inclusion" edit field.

Hi, you can add a Filter subnode to the Particle Trajectories plot type. You can only render a certain number or fraction of all the particles. In addition, you can also use a logical expression to pick out specific particles. Each particle is assigned a unique number, determined by the variable fpt.pidx (if fpt is the identifier for the Particle Tracing for Fluid Flow interface). You could use a logical expression like fpt.pidx==100 to only render the particle whose index is 100.

which logical expression should I write if I want to show for example particle number 2, 36, 97 and 100 in one plot?

Dear All,
Can we, for example, to label all the particles or rays in the graphics window as it is done for domains in the geometry node? Assume, that you have 50 rays or particles rendered. How can I understand to which particle or ray which index is assigned?

If you have only a couple of particles, then I suggest that you add a Color Expression attribute to the Particle Trajectories plot. For many particles it's probably better to use a Derived Values > Particle Evaluation node.

I cannot still figure out from your words how to evaluate a certain index assigned to a certain particle or a ray. Ultimately, I can just iterate through all the particles or rays by typing '{interface name}.pidx==X' (where X is the number of a particle or a ray), but it is a humdrum and cumbersome job. Could you please explain further what should I do?

I cannot still figure out from your words how to evaluate a certain index assigned to a certain particle or a ray. Ultimately, I can just iterate through all the particles or rays by typing '{interface name}.pidx==X' (where X is the number of a particle or a ray), but it is a humdrum and cumbersome job. Could you please explain further what should I do?

Have you tried using a color expression with the particle index, e.g., fpt.pidx, as expression?

No numbers can we render in the graphics window for each ray?

No numbers can we render in the graphics window for each ray?

This is correct.

You can't render the particle (or ray) index in the Graphics window, you can set the Color expression to interface.pidx (or interface.ridx for rays), then set the "Point style" to "Point" in the "Particle Trajectories" plot. You can then click on the rendered point for the particle (or ray) in the Graphics window, and the particle index and its coordinates will appear in the results table below the graphics window. This is probably more convenient than adjusting the color or data range.

By interactively clicking on the particles you want to isolate, you can use their index in the logical expression of the filter node as discussed above.