CASA can be run from a desktop shortcut or the Start Menu, and will start with an empty model and default settings. Upon original installation the file suffix .casa is associated with CASA, and so an alternative means is to double-click on such a file to cause CASA to automatically load with the file.
When CASA is run, the main window opens and is referred to as the main window or model view or structure view, depending on the context. This window displays the graphical view of the structure and provides access to the main tools needed to create and process the model.
Other windows which are used to edit data and perform specific tasks are called dialogue windows or editing windows. There can be as many or as few of these as you wish, and they need only remain open for as long as the task is being performed and can be closed afterwards to free up desktop space or you may leave them open if you prefer.
If you try to close the main window while the model has unsaved changes then a warning message appears and gives the opportunity to either keep the window open, save the model to disc, or close the model without saving the changes.
The engineer will probably be familiar with CASA’s modelling ideas. Nodes are defined at points in space, members are attached to the nodes, properties given to each member, supports attached to nodes, and then loads applied to nodes and members.
All of these things are called objects.
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CASA uses a fairly generic user interface. There is a main window which shows the structure being modelled, and along its top is a menu bar and toolbars. Of particular note are the Edit and View menus. The Edit menu gives access to the dialogue windows through which all of the objects and modelling data can be edited, and the View menu offers control over the appearance of the structural model in the main window.
The mouse is heavily used for interacting with the structural model through the view in the main window. In general, when entering data, such as references to nodes or members, if you can see it on the view then you can click on it instead of using the keyboard.
Creating and editing objects are one and the same thing in CASA; choosing a blank object and then entering values will automatically create a new object.
Objects are edited through their own editing dialogue windows. These dialogue windows can be opened from the Edit menu on the main window’s menu bar. Within each window, the object to be edited can be chosen from a drop-down menu containing the objects’ names. A blank object is available under the name “<new>”, and if used without specifying a name or number then one is automatically allocated. Alternatively, entering a name will assign that name to the new object.
When TAB or Return is pressed in the final input field, the input focus will return to the first input field and the next object will be automatically chosen.
Next to some of the input fields there are small green/red toggle buttons, “input locks”. When the toggle is green, the associated input field is expected to be filled in by the user. When it is red, the associated input field automatically takes its value from the last viewed pre-existing object and the input caret will automatically skip it when moving through the fields. This makes it easy to rapidly create new objects with data in common (e.g. lots of nodes with the same support type, or members with the same section type). Even when the button is red, the field can still be manually edited by clicking in it.
Where it is meaningful, objects can be dragged from their input window and dropped onto the structure in the main window or into other input windows to apply them to other objects. This makes it visually very intuitive when assigning supports, for example.
Most dialogue windows have pop-up context-sensitive menus, opened by clicking with the right mouse button on the window background. Typical functions accessed through these menus are deleting, renaming, and sorting.
CASA does not have nor needs a separate selection tool as such. Instead it treats a selection as part of the interaction with the model in the same way as for objects. Objects can be selected or deselected by clicking on them, dragging a rubberband, or en masse according to their attributes, e.g. every member of a particular section type.
Selections can be moved, copied, translated, and rotated, making it easy to generate multibay frames, meshes, spiral and helical staircases, or any other repetitive structure with only a few clicks of the mouse.
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