show flow - generate symbols to depict the flow in a field
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