Three-dimensional angle ϕ between the PCA axis and the line of sight to the cluster center as a function of distance for all 389 OCs in the T22 catalog. The OCs with more than 200 members are marked with gray filled circles, and those without structure parameters in the T22 catalog are marked with “×”. Red empty pentagrams are the selected golden sample OCs and are labeled with the cluster names. The red empty squares indicate IC 4756 and NGC 752, for reference. The horizontal gray dashed line represents the ϕ = 30° criteria, and the vertical gray dashed line indicates the 500 pc distance from the solar system barycenter.