AVS Modules show flow NOAA/ERL/Forecast Systems Laboratory NAME show flow - generate symbols to depict the flow in a field SUMMARY Name show flow Type mapper Inputs field, any-data, any-coordinates colormap (optional) field, any-data, any-coordinates (optional) upstream transform (optional, invisible) Outputs geometry Parameters Name Type Default Min Max Choices symbol type radio arrows arrows, barbs sample int integer 1 1, 100 symbol size float 1.0 0.0, unbounded unit arrow spd float 1.0 0.0, unbounded arrow scale mode radio scale by max scale by max, scale by avg, scale manually rotate symbols toggle off - X rotate float 0.0 unbounded Y rotate float 0.0 unbounded Z rotate float 0.0 unbounded freeze X aspect toggle off - freeze Y aspect toggle off - freeze Z aspect toggle off - DESCRIPTION The show flow module generates a geometry object named "flow symbols" that depicts the flow in a field of 1-, 2-, or 3-vectors of any data type and in any grid configuration. Show flow provides the same basic function as hedgehog but it has been enhanced to serve the meteorolog- ical community where wind barbs, rather than arrows, may be the desired flow symbol. Flow speed values are the resultant values of the field n-vector nalues. The symbols may be rotated about their reference points and their aspect with respect to the viewer can be frozen. While symbols of either type can be arbitrarily sized, arrows can be further scaled by a divisor which is the maximum of the field, the average of the field, or entered manually. The symbols will be colored by their speeds or the values in a second, optional field if an optional colormap is supplied. INPUTS Input Field (required, field, any-data, any-coordinates) The input field may be a 1D, 2D, or 3D field of any data type in any grid configuration. If the field contains scalar (1-vector) values, all of the symbols will point the same direction and the scalar values will be indicated by the "speed" component of the symbol. 2-vector values must be ordered U-V; 3-vector values, U-V-W. Vector components beyond the third position are ignored. Input Colormap (optional) If an optional colormap is supplied, the generated flow symbols will be colored according to where their resultant speeds or the values of the optional color field map into this colormap. If no colormap is supplied, the flow symbols will not be colored. Input Color Field (optional, field, any-data, any-coordinates) If this optional field is supplied, its values will be used to color the flow symbols, rather than the speeds derived from the required flow field. Only the values of this field are used, so it may be of any grid configuration. However, its computational dimensions must match those of the flow field. If no colormap is supplied, this field will have no effect. Transform Info (optional, invisible, upstream transform) In order for the any of the freeze aspect options to work, the show flow module must receive transformation data from the render geom- try module. AVS automatically makes this connection when the show flow module is instantiated. PARAMETERS symbol type Currently, arrows and wind barbs are the available symbol types. Arrows will have heads only if the shaft is longer than the length of the head. Wind barbs are become circles if the speed is less than 1.0. Show flow makes no determination as to what units of measure (knots, m/s, mph, milli-furlongs/micro-fortnight, etc) are associated with the data. A flag means 50 whatevers; a full barb, 10; and a half barb, 5. sample int The sample int parameter performs a local downsizing. Sampling always begins at the orgin corner point (1, 1, 1) and int-1 points are skipped in each direction of the field. symbol size For all symbol types, the symbol size parameter scales the entire symbol. A size value of 1.0 yields a symbol that is approximately the size of one grid interval in the input flow field. For arrows, additional scaling capabilites are available through the arrow scale mode parameter (q.v.). unit arrow spd arrow scale mode The unit arrow spd parameter indicates that speed which is indicated by an arrow of unit (one grid interval) length, before the size parameter is applied. If the arrow scale mode is set to "scale manually", the unit arrow spd widget is used to set the value by which all of the speeds will be divided. If the arrow scale mode is set to "scale by max", the maximum speed in the field is found and is used as the unit arrow speed. Similarly, if the arrow scale mode is set to "scale by avg", the average speed in the field is used. In either of the latter two cases, the unit arrow spd widget is updated with the derived value. rotate symbols X rotate Y rotate Z rotate The symbols of either type by be rotated about their reference points (head of the shaft for barbs, tail of the shaft for arrows). If the rotate symbols toggle is off, the rotation parameters are hidden and their values are ignored. Turning the rotate symbols toggle on makes the rotation parameters visible and enables their use. The values of the rotation parameters are in degrees. As an example, wind barbs, which are normally drawn in a horizontal plane, may be given an X rotation of 90 degrees to draw them in a vertical plane. The result is a presentation that looks like that of a wind profiler plot. freeze X aspect freeze Y aspect freeze Z aspect As a scene is transformed with the geometry viewer, the flow symbols may become oriented so that they become confusing or unreadable. As an attempt to remedy this problem, the viewing aspect of the symbols may can be frozen. Once a desirable viewing aspect has been chosen, the X, Y, or Z component of that aspect can be preserved. For example, if the scene is to be more or less rotated about its Z axis, freezing the Z aspect has the effect of undoing this rotation. The freeze aspect parameters are visible and enabled only if the rotate symbols toggle is on. OUTPUTS Output Geometry An object named "flow symbols" consisting of disjoint lines is created regardless of the symbol type. EXAMPLES This example combines a U field and a V field into a single field. Then this UV field is sliced and flow symbols are drawn on the slice. READ FIELD READ FIELD | | +-------+ +-------+ | | COMBINE SCALARS | ORTHOGONAL SLICER | SHOW FLOW | RENDER GEOMETRY | DISPLAY PIXMAP LIMITATIONS It is my intention to add more symbol types at a later date. This module has been used with uniform and "nice" irregular fields. It has not been tested with anything really weird. AUTHOR Phil McDonald, NOAA/ERL/Forecast Systems Laboratory NOAA/ERL/Forecast Systems Laboratory AVS Modules show flow