[Paraview] particle tracing and particle tails help

[Biddiscombe, John A.]

Dan, cc'ing paraview list again in case anyone else needs the information

1. You suggestion of using the 'Find Data' was great, but I found that I needed to use the  'ExtractSelection' before going ahead with the 'ParticlePathlines' filter.  From what you described that didn't seem necessary.  I suppose this came up particularly because in the ParticlePathlines filter once I extracted the selection I could simply set 'Mask Points' to 1 and take every particle in the carefully prepared selection.  Is the extract step necessary?

2. If ParticlePathlines is the way do to track explicit particles like mine, is there any use for the Particle Tracer outside of tracking the motion of injected seed particles over time within a vector field.

1 The find data was just a quick way of extracting particles by ID over time and yes, you need the extract selection filter. The particle trails filter actually has this function built in, it has a secondary optional input called 'selection'. On this input, you simply provide a dataset with (say) a field called ID which must match the IDs on the main dataset, if the ID exists in the selection, it'll be tracked in the main dataset. The reason I used the find data instead of just mask points was really because I assumed your Ids were nonsense (this is the top reason that people get no trajectories), and if the Ids were no good I guessed that using the find data (by ID) would for sure show me random movements. I could have done it using the pathline filter and mask points (and I did first time), but I was double checking to make sure things were as I thought.

Consider these cases for educational purposes ....
case a: You have a single time snapshot of your particles, each has an ID. You save this snapshot and select some interesting subset using a selection or maskpoints or whatever analysis you desire.. You now use this static dataset  as the secondary selection input of the trails filter and the main original time dependent dataset as the primary input *** those points with the fixed Ids from the selection are tracked from the dynamic dataset over T*** (note that if the Ids were actually wrong anyway, you'd get random tracks).

case b: You use the "find data" dialog to extract the Ids you are interested in and then draw pathlines for them. The Id extraction will update on each timestep and potentially give you different particles (if the Ids are wrong really). What you would now see is random tracks. I tried a and b to check your data and hit reply when b was still visible in my screenshot.

the difference between a and b, is that a selects ID's once and then builds tracks using the ID to find the particle. b extracts the particles using ID at each step and constructs the trails. They're sort of done in the opposite order and should give the same result for particular Ids. (you can combine a and b, but the pathline filter uses map and vector structures to x-ref particles, so having a large number of Ids selected will cause memory issues when long trails are used).


2 The Particle Tracer is for advecting particles in a vector field as you suggest and is of no use to you for what you are doing. Users of the particletracer can add a trails (pathline) filter to view the trajectories.


JB
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