A three-dimensional scatter plot is a trivariate plot in which a comparison of 3 measures is presented, one measure along each axis. To accommodate the two-dimensional display space (the VisiCube window or paper), a layering technique is utilized in which measurements along the vertical axis are accumulated into individual layers (of equal size). You are then presented with a 3D cube in which the position of the current layer is indicated and a 2D plot in which the data for that layer is accurately represented.
The following is a plot of data for the galaxy NGC 7531. In this data, measurements of the relative receding velocity of the galaxy, with respect to Earth, were taken at various positions in the galaxy. The positions are described by horizontal (East/West) and vertical (North/South) positions on the celestial sphere from the center of the galaxy. In this plot, the velocity measurements are divided into 10 layers and the third layer is displayed. (It contains the records with velocities between 1482 and 1519 km/sec.) Further, the records with velocities less than 1500 km/sec are brushed (in yellow) to distinguish the slower measurements from the faster ones.
Be aware that the 3D Scatter Plot in VisiCube can be animated (automatically or manually)...giving you the ability to compare all of the layers effectively and quickly. Here is shown just one of those layers.
In this layer, it is clear that while position generally determines velocity, it does not do so specifically. The general case is demonstrated by the location of all applicable records in the upper left (northwest) quadrant of the plot. However, the matching pattern and near-perfect overlap of the slower and faster records indicates that position, alone, does not totally determine velocity. It appears that there is something more complex involved in the motion of this galaxy. And, by scrolling through the layers, you can easily see that the velocity increases as the position moves to the south and east.
The data presented here is from R. Buta's study of the NGC 7531 galaxy, The Structure and Dynamics of Ringed Galaxies. III. Surface Photometry and Kinematics of the Ringed Nonbarred Spiral NGC 7531, which was published in 1987 as part of the Astrophysical Journal Supplement Series.
This data (and visual) is supplied with VisiCube as a sample project.
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