Flow Glyphs

Flow Glyphs showing AirFlow through an office
Flow Glyphs showing AirFlow through an office

Flow Glyphs are a method for visualizing vector flow in a data set.

Description

Generating flow glyphs for a vector flow field is a relatively simple endeavor. Simply placing a glyph at every data point, aligned to the flow, will quickly show the direction of the flow across the entire space. Further, by scaling the size of the glyph by the magnitude of the flow at that point, you can quickly locate areas of high-velocity flow by finding the larger glyphs. The glyphs used can range from simple lines to more complex shapes such as arrows or cones.

Problems

  1. Cluttered Visualization - In a large data set, placing a glyph at every point may lead to a visualization so crowded that no useful information can be extracted from it. In such a case, subsampling is used to place a specified number of glyphs within the data set. The subsampling used can be either an "Every Xth Point" method, or simply randomly selecting points within the space.
  2. Glyph Sizing - Many times the velocity scale is much greater than the grid scaling, leading to glyphs that encompass several cells. This can be overcome with a simple static scaling applied to all the glyphs.

Uses

Flow Glyphs are useful for quickly visualizing an entire flow field at once. Unlike other operations like Streamlines or Line Integral Convolution, flow glyphs are fast and relatively simple to compute. While themselves useful for seeing trends in the flow, flow glyphs are also a good first step in finding seed points for more complex visualizations such as Streamlines or Pathlines.

However, flow glyphs are not very useful for visualization of Transient Data, as the glyphs are actually fixed in space and simply grow or rotate to match the flow.


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