QCFC Distance Dependence

Distance-dependence of QC-FC measures.

qcfcDistanceDependence computes the distance-dependence of QC-FC relationships previously estimated using qcfc. (Although it was designed for diagnosing the distance-dependent profile of motion artefact, qcfcDistanceDependence can be used to compute the distance-dependence of any edgewise measure.)

qcfcDistanceDependence executes in the following order, using its inputs as follows:

  1. Read in the atlas specified by the -a flag.
  2. Call cmass to estimate the centre of mass of each node in the atlas.
  3. Call distmat to estimate the pairwise Euclidean distance between nodal centers of mass, saving the output as a distance matrix to the path specified by the argument to -d.
  4. Correlate the computed pairwise distances with the test values provided as an argument to -q, saving the overall correlation to the path specified by the argument to -o.
  5. Plot a cloud of edgewise values with the Euclidean distance on the abscissa and with the test value on the ordinate; write the plot to the path specified by the argument to -f.


  • The distance-dependence of provided test values, defined as the edgewise correlation coefficient between the test values and Euclidean distance (specified by argument to -o).
  • A matrix of internodal Euclidean distances (specified by argument to -d).
  • A plot of the relationship between test values and Euclidean distances (specified by argument to -f).

Input arguments

Running from Docker::

docker run --rm -it --entrypoint \
/xcpEngine/utils/qcfcDistanceDependence \
  pennbbl/xcpengine:latest \
  –a <atlas> \
  -q <test values> \
  -o <output path> \
  [-d <output distance matrix> -f <output correlation plot> -i <intermediate output>]

Optional arguments are denoted in square brackets ([]).

-a: Atlas

The atlas over which inter-nodal distances should be computed. This atlas should also have been used to define the test values.

-q: Test values

A file containing an edgewise vector of values to evaluate for distance-dependence. Often, these will be the QC-FC estimates produced by the qcfc utility.

-o: Output

The path where the overall correlation coefficient between distance and test values should be saved.

-d: Distance matrix

The path where the matrix of distances between each pair of nodes in the provided atlas (argument to -a) is saved.

-f: Save correlation plot

The path where the scatter plot of edgewise distance and test values will be saved. If ggplot2 and reshape2 are not installed, then the plot is automatically disabled.

-i: Intermediate output path

A path where erodespare stores temporary files. If your machine or file system has a designated space for temporary files (e.g., /tmp), then using this space can substantially improve I/O speed. Note, if running through Docker or Singularity your directories will need to be mounted correctly.