Blob Track CHOP


The Blob Track CHOP allows tracking blobs in 2D point data.

Input data should be have two channels named tx and ty describing the 2D points in cartesian coordinates. See the OP Snippets examples.

Good sources for input scans are the Hokuyo CHOP (in Cartesian coordinate mode) and the Leuze ROD4 CHOP. These devices naturally output a radial scan from the device as the center point, where each point represents (angle, distance). Outputting each scan point in Cartesian coordinate mode gives an (x,y) for each point which is the format required for the Blob Track CHOP.

But any set of (x,y) points in the two channels will be analyzed. The tracker looks for consecutive points close to each other, and handles the case where one blob passes behind another blob giving the hidden blob a linear motion for a specifiable amount of time while it occluded before it removes the blob from the set of blobs being output.

See also Blob Track TOP


Parameters - Tracker Page

Active active - While on, the CHOP receives information from the input. While off, no processing occurs. Existing blobs will remain.

Search Mode searchmode - - Controls how searching for blobs is done across all the points.

  • All all - All the points are compared against each other to find blobs. This mode is slower but more robust for data that has the points randomly assorted in the CHOP.
  • Consecutive Points consecutive - Points are only compared against points in neighbouring samples of the CHOP data to find blobs. This is much faster but the data much be setup such that points that are close to each other in space are next to each other in the CHOP samples. Data coming from devices such as the Hokuyo CHOP and Leuze ROD4 CHOP output data in this format.

Max Blobs maxblobs - The maximum number of blobs that can be tracked.

Max Point Distance in Blob maxpointdistance - Two measured points from the input are considered to be part of the same blob if they are this distance or closer to each other.

Max Blob Movement maxblobmovement - This controls the maximum distance a blob can move between successive frames and still be considered the same 'blob'.

Area of Interest areaofinterest - - Limits the area in which blobs are tracked. Points outside the area of interest are ignored.

  • Off off - No limitations, blobs tracked throughout the scanned area.
  • Rectangle rectangle - Blobs only tracked within specified rectangle.
  • Circle circle - Blobs only tracked within specified circle (or ellipse).

Center center - - The center of the area of interest.

  • Center centerx -
  • Center centery -

Size size - - The size of the area of interest.

  • Size sizew -
  • Size sizeh -

Rotate rotate - Rotate the area of interest.

Allow Movement Outside Area allowmovementoutside - When this is on, blobs detected within the Area of Interest can move outside of that area and still be tracked. When this is off blobs that move outside the area of interest will stop being tracked.

Parameters - Blobs Page

Output Centroid outputcentroid - Include the centroid of detected blobs as part of the output channels.

Output Velocity outputvelocity - Include the velocity of detected blobs as part of the output channels.

Min Points per Blob minblobpoints - Minimum number of points that must be near each other to form a blob. Use to help filter out false positives.

Blob Init Time (s) blobinittime - Amount of time a blob must be detected to be considered trustworthy. Use to help filter out false positives. A blob will only be output if it's been detected for at least time amount of time.

Lost Blob Timeout (s) lostblobtimeout - The amount of time before a blob that has been lost is removed from the output.

Blob Movement Prediction Type predicttype - - With prediction enabled, blobs from the last frame have their new position predicted before being matched to the current frame.

  • Off off - Blobs are matched against the blob positions from the last frame.
  • Simple Forward Predict simple - Prediction uses constant velocity assumption; blobs are moved the same distance that they moved last frame.
  • Kalman Filter Predict kalman - Prediction uses kalman filtering, with a constant velocity model, to move the blobs forward from last frame.

Parameters - Common Page

Time Slice timeslice - Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.

Scope scope - To determine which channels get affected, some CHOPs use a Scope string on the Common page. See Pattern Matching.

Sample Rate Match srselect - - Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.

  • Resample At First Input's Rate first - Use rate of first input to resample others.
  • Resample At Maximum Rate max - Resample to the highest sample rate.
  • Resample At Minimum Rate min - Resample to the lowest sample rate.
  • Error If Rates Differ err - Doesn't accept conflicting sample rates.

Export Method exportmethod - - This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.

  • DAT Table by Index datindex - Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
  • DAT Table by Name datname - Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
  • Channel Name is Path:Parameter autoname - The channel is the full destination of where to export to, such has geo1/transform1:tx.

Export Root autoexportroot - This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.

Export Table exporttable - The DAT used to hold the export information when using the DAT Table Export Methods (See above).

Operator Inputs

  • Input 0: -

Info CHOP Channels

Extra Information for the Blob Track CHOP can be accessed via an Info CHOP.

Specific Blob Track CHOP Info Channels

  • num_blobs -

Common CHOP Info Channels

  • start - Start of the CHOP interval in samples.
  • length - Number of samples in the CHOP.
  • sample_rate - The samplerate of the channels in frames per second.
  • num_channels - Number of channels in the CHOP.
  • time_slice - 1 if CHOP is Time Slice enabled, 0 otherwise.
  • export_sernum - A count of how often the export connections have been updated.

Common Operator Info Channels

  • total_cooks - Number of times the operator has cooked since the process started.
  • cook_time - Duration of the last cook in milliseconds.
  • cook_frame - Frame number when this operator was last cooked relative to the component timeline.
  • cook_abs_frame - Frame number when this operator was last cooked relative to the absolute time.
  • cook_start_time - Time in milliseconds at which the operator started cooking in the frame it was cooked.
  • cook_end_time - Time in milliseconds at which the operator finished cooking in the frame it was cooked.
  • cooked_this_frame - 1 if operator was cooked this frame.
  • warnings - Number of warnings in this operator if any.
  • errors - Number of errors in this operator if any.

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