Special Variables and Data Values

Analysis and visualization of wind information is an important part of Vis5D. Specifically, the vis5d program looks to see if your data set contains variables named U, V and W. If present, they are assumed to be the three components of wind vectors and are used to display trajectory tracings and wind slices.

The U wind component is parallel to rows, with positive U values pointing toward increasing column numbers (i.e., positive eastward in a cylindrical equidistant map projection). The V wind component is parallel to columns, with positive V values pointing toward decreasing row numbers (i.e., positive northwardward in a cylindrical equidistant map projection). Positive W values are upward, negative W is downward. The units for U, V and W are assumed to be meters per second except when a generic map projection or vertical coordinate system is used. In that case, the units are in X per second where X is the units used to specify the northbound, westbound, rowinc, and colinc parameters.

If you do not like to use U, V, and W for wind vector components you can either specify other wind variable names on the vis5d command line or enter them while running vis5d.

Strictly speaking, U, V and W do not have to represent wind motion. They can be used to represent any flow field such as ocean currents. However, you may want to scale U, V, and W by some constant for visualization purposes.

Vis5D allows any grid data value to be undefined or 'missing'. For example, datasets based on observations are often incomplete or contain erroneous values. In your data conversion program you can indicate a grid value is missing by assigning it a value greater than 1.0e30. Missing data in vis5d will show up as holes in isosurfaces and contour slices and as black regions in colored slices. The data probe will report missing values as 'Missing'.