areaDetector Plugin NDPluginOverlay

Contents

• Overview
• Configuration
• Screen shots

Overview

NDPluginOverlay adds graphics overlays to an NDArray image. It can be used to highlight ROIs on an image, to implement cursors, add text annotation, and other similar operations. It supports any number of overlay objects. For each object there is control of the location, size, line width, color, and drawing mode. The size, line width and location can be directly controlled, or links can be used to control the position and size from other PVs. For example, links to the PVs definining an ROI in the NDPluginROI plugin can be used to define a rectangular overlay in thus plugin. Similarly links to the PVs defining the X and Y centroid and sigma of an image computed in the NDPluginStats plugin can be used to control the location and size of a crosshair overlay in this plugin. The cursor will then follow the location of a "beam" in the image. Putting such graphics overlays into an areaDetector plugin allows the use of simple image display clients, which don't need to compute the graphics themselves.

Each NDPluginOverlay plugin can contain any number of overlay objects, each with a different shape, position, color, etc. The number of overlay objects is defined when the NDPluginOverlay is created in the startup script. Each object is referenced by its asyn "addr" address field.

NDPluginOverlay is both a recipient of callbacks and a source of NDArray callbacks. This means that other plugins, such as the NDPluginStdArray plugin, can be connected to an NDPluginOverlay plugin. In that case an image display client will receive the arrays with the graphics overlays.

NDPluginOverlay can only be used for 2-D arrays or 3-D color arrays, it is not fully N-dimensional.

NDPluginOverlay inherits from NDPluginDriver. The NDPluginOverlay class documentation describes this class in detail.

NDPluginOverlay.h defines the following parameters. It also implements all of the standard plugin parameters from NDPluginDriver. There are 2 EPICS databases for the NDPluginOverlay plugin. NDOverlay.template provides access to global parameters that are not specific to each overlay object. There are currently no records in this database, because it currently needs nothing beyond what is contained in NDPluginBase.template, but there may be records added to this in the future. NDOverlayN.template provides access to the parameters for each individual overlay object, described in the following table. Note that to reduce the width of this table the parameter index variable names have been split into 2 lines, but these are just a single name, for example NDPluginOverlayName.

Display limits for Position and Size fields

It is very convenient to have slider widgets to control the size and position of user-defined overlays. For these to work correctly, the HOPR fields of the X and Y position and size widgets must be set to the maximum allowed values. This is handled in the NDOverlay.template database, where the HOPR fields are automatically set to the actual size of the input array whenever that changes. Note that if HOPR changes, then with medm it is necessary to close and reopen the display with the sliders, because medm only retrieves the value the display limits when it first connects to a channel.

Configuration

The NDPluginOverlay plugin is created with the NDOverlayConfigure command, either from C/C++ or from the EPICS IOC shell.

NDOverlayConfigure(const char *portName, int queueSize, int blockingCallbacks,
                   const char *NDArrayPort, int NDArrayAddr, int maxOverlays,
                   int maxBuffers, size_t maxMemory,
                   int priority, int stackSize)
  

For details on the meaning of the parameters to this function refer to the detailed documentation on the NDOverlayConfigure function in the NDPluginOverlay.cpp documentation and in the documentation for the constructor for the NDPluginOverlay class.

Screen shots

The following is the MEDM screen that provides access to the parameters in NDPluginDriver.h and NDPluginOverlay.h through records in NDPluginBase.template and NDOverlay.template. This screen does not provide anything beyond the PVs in NDPluginBase.template except for the menus to call up the related displays.

NDOverlay.adl

The following is the MEDM screen that provides access to the parameters in NDPluginOverlay.h through records in NDOverlayN.template. This allows control of the parameters of a single overlay object.

The following is the MEDM screen that provides control of most the parameters of 8 overlay objects, and a link to the screen above for each one.

Image display from ImageJ where the cursor is set to track the centroid of a laser pointer via its X and Y center input links from the NDPluginStats plugin.