Transform class

The Transform class provides its subclasses with the ability to handle coordinate transformations.

Synopsis

Header file:		ncarg/hlu/Transform.h
Class name:		transformClass
Class pointer:		<Not referenceable>
Fortran class function:	<Not referenceable>
Superclass:		View
Composite classes:	<None>

Resources

Local resources

+---------------------------------------------------------------+
|			Transform Resource Set			|
|---------------------------------------------------------------|
| NAME				TYPE			ACCESS	|
|	CLASS				DEFAULT			|
|===============================================================|
| tfDoNDCOverlay                NhlTBoolean             RCSG    |
|       TfDoNDCOverlay                  False                   |
|---------------------------------------------------------------|
| tfPlotManagerOn               NhlTBoolean             RCG     |
|       TfPlotManagerOn                 True                    |
+---------------------------------------------------------------+

Composite resources

The Transform object class has no composite class resources.

Superclass resources

For any Transform class object, you can set all resources defined by the Transform class's superclasses, including:

View resources

Description

Objects that belong to the Transform class are viewable objects that support transformations between data coordinate space and NDC space. A Transform object may be called simply a transform. Most Transform subclasses have their own specialized plot elements that you can render by calling the object's Draw method.

Transformation composite class

All subclasses of Transform include as a composite class member at least one subclass of the Transformation class to perform the forward and reverse transformations. There are currently three Transformation classes available to the subclasses of Transform:

The LogLinTransformation provides transformations to and from a linear or logarithmic coordinate space. Either or both coordinate axes may be logarithmic.
The IrregularTransformation provides transformations to and from rectangular coordinate spaces where each coordinate axis may be either irregularly spaced, linear, or logarithmic.
The MapTransformation provides transformations to and from any of 10 different standard map projections.

PlotManager composite class

Subclasses of the Transform class may contain the PlotManager class as a composite class member. The PlotManager manages annotations and data space overlays on behalf of the transform. A transform instantiated with an active PlotManager is is known as a plot object.

Graphics primitives

In addition to their specialized plot elements, objects belonging to the Transform class have the ability to act as a "canvas" for drawing arbitrary graphics primitives. You may specify these primitives in data space using the NhlDataPolyline, NhlDataPolygon, and NhlDataPolymarker routines or in NDC space using the routines NhlNDCPolyline, NhlNDCPolygon, and NhlNDCPolymarker. When drawing in data space, lines between the points supplied as parameters to the NhlDataPolyline and NhlDataPolygon routines are rendered in the data space: if the space is curved, these lines will be curved as well.

These graphics primitive functions all operate in immediate mode: they appear as part of the Workstation output as soon as the functions execute. They are not part of the object in the same sense as the object's plot elements since they do not appear as a result of calling the object's Draw method. Currently, there is no way to save these primitives for later manipulation or reproduction.

Support functions

Transform defines the following support functions:

NhlNDCToData: Given arrays containing the X and Y coordinates of points in NDC space, the NhlNDCToData function returns arrays containing the X and Y coordinates of the same points in data coordinate space.
NhlDataToNDC: Given arrays containing the X and Y coordinates of points in data coordinate space, the NhlDataToNDC function returns arrays containing the X and Y coordinates of the same points in NDC space.
NhlDataPolyline: Given arrays containing the X and Y coordinates of points in data coordinate space, the NhlDataPolyine function outputs an immediate-mode polyline connecting each of the points. Intermediate points between the given points along the path of the line segments in data space are sampled in order that the output polyline represents the path of "straight" line segments in data space. The resulting polyline may therefore appear curved in NDC space.
NhlNDCPolyline: Given arrays containing the X and Y coordinates of points in NDC space, the NhlNDCPolyine function outputs an immediate-mode polyline connecting each of the points.
NhlDataPolygon: Given arrays containing the X and Y coordinates of points in data coordinate space, the NhlDataPolygon function outputs an immediate-mode polygon consisting of a filled area and an optional edge with the points at the vertices. Intermediate points between the given points along the path of the line segments in data space are sampled in order that the edges of the output polygon represent the path of "straight" line segments in data space. The resulting polygon may therefore appear curved in NDC space.
NhlNDCPolygon: Given arrays containing the X and Y coordinates of points in NDC space, the NhlNDCPolygon function outputs an immediate-mode polygon consisting of a filled area and an optional edge with the points at the vertices.
NhlDataPolymarker: Given arrays containing the X and Y coordinates of points in data coordinate space, the NhlDataPolymarker function outputs immediate-mode markers at each of the points.
NhlNDCPolymarker: Given arrays containing the X and Y coordinates of points in NDC space, the NhlNDCPolymarker function outputs immediate-mode markers at each of the points.
NhlIsTransform: This function just determines if a given object id identifies a Transform class object.

The following support functions are used to add overlays and annotations to plot objects, and also to remove them.

NhlAddOverlay: The NhlAddOverlay function adds transform as an overlay of a base plot.
NhlRemoveOverlay: The NhlRemoveOverlay function removes an overlay from a base plot.
NhlAddAnnotation: The NhlAddAnnotation function adds an arbitrary user-created View object to a plot object as an annotation, returning the id of a controlling AnnoManager object.
NhlRemoveAnnotation: The NhlRemoveAnnotation function removes the association between a user-created View object and the plot object to which it belongs as an annotation. It destroys the controlling AnnoManager object.

Status

Copyright

Copyright 1987-1999 University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.

NCAR Graphics is a registered trademark of the University Corporation for Atmospheric Research.

Reference Manual Control Panel

NG4.1 Home, Index, Examples, Glossary, Feedback, Ref Contents, Ref WhereAmI?

$Revision: 1.26 $ $Date: 1998/08/18 08:15:22 $