16 Glossary

Checkbutton

A common GUI component which consists of a row or column of small boxes (or buttons), each button can either be on (coloured) or off. Each box has a label which tells you what the box controls. You make a choice by clicking the mouse over one of the small buttons. The checkbutton is closely related to the radio button, but differs in that any combination of Checkbuttons can be chosen (on).

Client/Server

A term used to describe a type of interaction between two networked computers. In this case the Server computer provides some service (eg reducing extra-focal images) to another computer, the Client. Typically service requests and data are transmitted between two computers over a network.

Cursor

A block of pixels on screen which shows you the current position of something. For instance a cursor marks the current position of the insert point in an editor, and another cursor marks the current position of the screen pointer (mouse).

Dialog

A dialog is a temporary window containing information and/or data entry fields. Dialogs appear in response to your selecting a menu item, or to inform you of errors. Some dialog boxes perform a focus grab which means you must respond to the dialog (usually by pressing the ok button) before you can proceed with using the program. Where ever possible we have avoided using a focus grab.

Extra-focal image

We use the term extra-focal image to refer to an image plane before or after the best focus of the optical system. This can be thought of as a de-focused image, or more useful from our point of view, as a de-focused pupil image.

Focus

This word has distinct optical and a computer meanings.

In a GUI, input from the keyboard and pointing device is channeled into various applications by a program called an event notifier. Usually the position of the pointing device determines which program, or program part receives keyboard and other events. The program or program part which is currently receiving input, is said to have the input focus.

In the optical sense focus is the position at which the light from a point source reaches its smallest spatial extent. Depending on the exact criterion used to define "smallest", the focus portion may shift slightly.

Focus Grab

Sometimes an event so serious happens, that the program writer would like the user to deal with the event before anything else happens. This is most usually in response to a serious program error. In this case a particular program can grab all input to the system, giving it the focus of all input events, this effectively blocks all other programs and forces the user to deal with the problem. This mechanism is quite rude, so we have tried to avoid it as much as possible.

GUI

GUI stands for Graphical User Interface. Usually this refers to a system of windows and buttons on a computer screen with which you interact using a pointing device and your keyboard. The most well known examples of GUI interfaces are the Macintosh system, XWindows and MS-Windows.

Listbox

The listbox is a common GUI device for displaying a large number of options. The options are displayed 1 per line in a window, a scrollbar attached to the window allows the user to move through the complete list of available options. An option is usually selected using th pointing device (clicking the mouse over it).

Pointing device

A piece of hardware, eg a mouse or trackball, which allows you to select any point on a computer screen.

Radio button

A common GUI component which consists of a row or column of small boxes (or buttons). Each box has a label which tells you what the box does. You make a choice by clicking the mouse over one of the small buttons. The radio button typically allows you to choose only one of the options, when you click on a button, it will become active, and the previously active choice will be cleared. This single choice behavior is reminiscent of the behavior of the band selection buttons that can be found on some antique radios and televisions, and is probably where this interface component got its name.

Regular expression

A regular expression is a flexible and powerful format for specifying patterns of text. A full description of regular expressions is beyond the scope of this manual. For use in this program, probably all you need to know is that the "." character stands for any character, and the "*" character stands for any number of occurrences of the previous character. Thus the sequence ".*fits" matches any string ending with the letters "fits". Notice this is a little different from the wild-card that would be used with an MSDOS or UNIX command line, namely "*fits".

RPC

RPC stands for Remote Procedure Call. It is a method of distributing an application over two or more networked computers. One arranges for a certain set of functions to be transparently executed on remote machines. A mechanism (the program rpcgen and an rpc library, or the dp package) takes care of all the network transport details such that merely calling one of the networked functions causes it to be executed on a remote machine. The attractiveness of this method is that it makes network programming almost transparent.

Scroll bar

A common GUI device, which enables the display of objects which are too big for the physical screen. The extent of the scroll bar represents the size of the object. Inside the scroll bar is a small "cursor" which represents the currently displayed segment of the object. You display a different part of the object by moving the cursor within the scrollbar using your pointing device.

TCP/IP

Stands for Transmission Control Protocol/Internet Protocol. This is a specification for a network transport layer. It is the software which actually looks after the details of sending data from one computer to another.

Wavefront

An optical wavefront is a surface of constant optical phase. For a perfect optical system the wavefront converging to a focus would be a perfect sphere, or at the entrance pupil, a perfectly flat surface. Optical aberrations cause the wavefront surface to deviate from this ideal case. It is the purpose of the ef program to compute the difference between an ideal wavefront and the actual wavefront produced by an optical system.