Picking

There are two pick tools in form•Z:

Pick.tif Pick, and Pick Area Marquee_New 2.tif Area Pick.

These tools allow you to select objects, object parts, lights, guides, and other graphic entities in a project window. Picking serves two main purposes: (1) Selecting one or more entities so that an operation may be applied to them. (2) Selecting an entity so that its attributes and parameters may be shown and edited.

 

Prepicking and postpicking

In form•Z, entities can be picked with one of the pick tools or directly with one of the other tools that apply operations to entities. When a pick tool is used to pick one or more entities and then another modeling tool is activated and applied to the picked entities is called the prepick method. When a modeling tool is used directly to both pick an entity and apply an operation is called the postpick method. Which method is preferable depends on the circumstances.

 

For a prepick example, with the Pick tool select one or more objects. Then activate the Move tool and click once to start moving and one more time to end moving. Notice that, after ending the move, the objects remain highlighted. Alternatively, the postpick method can be used. Activate the Move tool directly and with it click on an object to start the move. Then click again at another location in the project window to end the move. Notice that, in this case, the object is not highlighted after the operation is completed. We discuss a bit later how to postpick more than one object.

 

Previewing the picks

When form•Z expects a pick, moving the cursor over an entity will draw the entity in a dimmed version of the highlight color (by default pale red). This will give you a preview of what would be picked if you were to click at this point. This is referred to as preview picking. Once clicked, the picked entity is drawn in the full highlight color. When moving the cursor over an already picked entity, the pale preview highlight is drawn as a dashed line on top of the full highlight. There is an option for toggling this feature on/off under the Edit menu, called Selection Preview.

 

Pick previews can be done with all pick tools and the other modeling tools. While the pick tools will preview all the pickable entities, each modeling tool is programmed to pick preview only the entities that are acceptable to its particular operation. For example, a roof is only generated from a closed, flat face of an object and cannot be generated from a complete solid. When previewing picks with the Roof tool, it will only highlight the flat faces of objects.

 

When activating a tool with one or more entities prepicked and some of these entities are not suitable for the operation, the offending entities are automatically removed from the picked set. For example, the Reshape tool only works on planar faces. If you prepick two planar and two spherical faces with the Pick tool and you then activate the Reshape tool, the spherical faces will be unpicked.

 

Picking complete versus parts of object

pick_tool_options.jpg
The Pick Tool Options palette.

form•Z allows you to pick entire objects or parts of objects and is affected by the Topological Level icons found in its Tool Options palette. The first icon on the far left is Auto Pick.

 

When the Pick tool and the Auto Pick topological level are active, moving the cursor over an object highlights the entire object and clicking at that point will select the entire object. To select a face, curve, segment, or point of an object you need to move the cursor over the object part you want to pick and press the command key (Macintosh) or ctrl key (Windows). This will change the preview pick from the object to the object part you are pointing to. For example, if the cursor is directly over a segment, that segment will be picked and highlighted. If the cursor is over a face, not close to a segment, the face will be highlighted, etc. Clicking with the command/ctrl key down will pick the highlighted object part.

 

The seven icons to the right of Auto Pick correspond to Point, Segment, Segment Sequence, Outline, Face, Hole, and Object. Selecting one of these icons tells form•Z exactly what to pick when you place the cursor and click over a respective entity.

 

It generally takes one click to pick an entity at any topological level. However, faces, outlines and holes can also be optionally picked with two edge clicks. This is controlled by the 2 Click Face/Outline Selection in the Edit menu, which is, by default, off for Shaded rendering and on for Wire Frame. The 2-click method picks faces with both the Auto Pick and Face topological levels. For outlines and holes it only works with the Outline and Hole topological levels, respectively.

 

Selecting one of these icons tells form•Z exactly what to pick and so it does when you place the cursor and click over a respective entity.

 

Moving and copying with the Pick tool

The Pick Tool Options palette contains two options that allow you to execute a move and a copy operations with the Pick tool.

 

Allow Drag: when on, you can click and drag an entity (complete object or part) to move it to another location, without resorting to the Move tool.

 

Allow Copy: When on and you click and drag an entity while pressing the option (Macintosh) or alt (Windows) key, a copy is dragged and placed at the final position of the mouse.

 

Pick parade

Frequently, a part of an object may belong to more than one topological level. For example, a hole is also part of a face, which in turn belongs to a complete object. Thus placing the cursor on a point and clicking on it could potentially pick any of the above entities and the program has no way of knowing what is the intention of the user. In such cases the ability to parade through all the choices while previewing the possible picks is available. When the desired entity is highlighted, clicking selects that entity.

 

To parade through all the possible picks, place the cursor over the object part, then hit and release the tab key. The next best object part will be highlighted. Hitting the tab key repeatedly will cycle through all the choices available. When you see the entity you want to pick, clicking will select it.

 

Picking multiple entities

By default, clicking on an entity (with or without the command/ ctrl key pressed) that is not picked, selects just that entity. Other entities, that may have been picked will be deselected. If an entity is already picked and you click on it again, nothing will happen.

 

If you want to pick more than one entity, hold the shift key down, and click on additional entities that are not already picked. Clicking on an already picked entity, while pressing the shift key, deselects that entity. Whether an object will be added or removed is indicated with a “-” or “+” sign next to the cursor while the shift key is pressed.

 

Whether the shift key is required or not for multi-picking is controlled by the Use Shift Key For Multiple Pick option in the Project : Modeling : General tab of the Preferences dialog that can be invoked from the form•Z menu (Windows) or the Edit menu (Macintosh). This option is on by default. If turned off, you will be able to multi-pick without having to press shift.

 

Picking sets

Many tools can only be applied to single objects. In these cases, using the postpick method, with the tool active, you just click on an object. Many other operations require more than one operands and frequently the number of operands may vary. For example, the loft operation, can generate a lofted object from a minimum of two shapes or it can generate an object from a larger number of shapes. Each tool knows what is the minimum number of objects it requires. When the minimum number is used, the operands can be picked directly. When more than the minimum number are used, they have to be picked as sets. Following is how you pick a set:

You have just completed picking a set. If the tool needs another object to be picked, if you intend to use the minimum number required, you just click on the object(s). If you intend to use more than the minimum requirement, you have to pick another set, as you did above.

 

If a tool is activated with one or more objects already picked, they are considered to comprise set one. No more objects can be added to set one, using postpick. Postpicking will proceed for the selection of the objects in set two, as before. That is, with shift pressed, click on the objects of set two, then release shift and click away from any pickable object. The operation will be executed as soon as you click.

 

Another example of an operation that is often used with just two operands and is often also used with multiple operands is the Boolean Difference. When applied to just two objects, they are picked directly and there is no need to pick sets of objects using shift. In contrast, when a number of objects have to be subtracted from a number of other objects simultaneously, these two groups of objects have to be picked as sets, using the shift key.

 

Area picking

area_pick_tool_options.jpg

The Area Pick Tool Options palette.

 

 

The Pick tool can also be used to execute area picking, more specifically called frame picking, as it always uses a rectangle to pick. To frame pick, you click on an empty area of the screen and drag. Which entities are picked depends on the selection from the Frame popup menu.

 

Off disables the frame picking. Inside Only pick only the entities that are completely contained in the rectangular frame. Crossing Left-Right picks all the entities that are contained and also the entities the frame crosses when it is drawn from left to right. Crossing Right-Left is exactly the opposite for crossing entities. Crossing Always picks all the entities it contains and it crosses regardless of the direction in which it is drawn.

 

The drawing of the picking frame can also start by clicking on a non-empty area of the screen, if the shift key is pressed.

 

In addition to area picking using the Pick tool, there is a special tool, the Area Pick tool, which allows you to area pick multiple entities using variable shapes. This tool can pick at any topological level, which is selected from its Tool Options palette.

 

The area to be picked may be outlined with one of three shapes: Rectangle, Lasso, or Polygon. This is selected from its Options palette. The default is the rectangle.

 

The Pick Crossing option determines whether the entities to be picked should be completely enclosed by the drawn area shape, or whether it will suffice to be crossed by the shape. By default this option is off, which means that the entities need to be completely enclosed.

 

The Select/Deselect option determines whether the objects or parts of objects identified by the drawn shape are added to or removed from the entities that are already picked.

 

Changing attributes and parameters with the Pick tool

The attributes and parameters of the picked entities are displayed in the Tool Options palette, which consists of up to four tabs, as follows:

 

Selection tab: This tab contains information about how many entities are currently selected.

 

Attributes tab: If one or more objects or faces are selected, this tab shows the value of the object or face attributes. For example, it shows whether an object casts shadows or not in the check box Casts Shadows. Clicking in the check box turns the attribute on or off for all selected objects. If some of the objects selected had this attribute set to on and others off, the check box shows a “-” indicating that the attribute varies among the selected entities. The same principle applies to all attribute values shown in this tab. The tab is further organized in attribute categories, which can be selected from the menu at the top of the tab.

 

Another example would be Show Face Normals. The normals are vectors perpendicular to a surface. When this option is on, the normal vectors of all faces are also displayed. This option is off by default. Note that, when objects have dense faces, the normals may be hard to read. In such cases displaying the objects with their back faces eliminated improves their readability. Another method for improving the readability of the normal vectors is to select individual faces. When faces are selected, their normals are also highlighted, which makes it easier to see which normal corresponds to the selected face.

 

Component Import Options
The Layer Override in Effect.
Component Import Options
The Component Override in Effect.

Component instances have there own override attributes. That is when an attribute like the material or shadow casting of a component is changed, it is applied to the placed instance and there is no prompt to update the component definition. This is works for all of the basic object attributes.

 

Overridden attributes can be cleared when a component is selected with the Restore Original Attributes button in the Parameters tab of the Tool Options – Pick palette.

 

Examples of Component overrides are shown on the right. A yellow exclamation point is displayed to the right of the attribute that it has been overridden. This means that the original Component definition has not been updated, and placing new instances of the component will place them without the overrides. This allows a single component to display differently as various instances, and any changes to geometry in the original Component file can be propogated to the instances without disturbing Component overrrides.

 

 

Info(rmation) tab: This tab contains more information about the selected objects or faces, such as the object type, the origin, and rotation of the object. If more than one object is selected, the information is cumulative.

 

Parameters tab: If only one object is picked and the object is a controlled object, its parameter values are shown in this tab. Changing a value will automatically update the object. If entities other than objects are picked, this tab will not be shown.

 

When multiple objects of the same type are selected and no objects of any other type are selected, the parameters of the objects are displayed and can be edited. When a parameter is the same among the selected objects, then that value is shown in the normal fashion. When a parameter is changed, it is applied to all of the selected entities.

 

If a parameter is different between any two objects, then it is displayed differently to indicate that there are multiple values present. Text field parameters (usually numbers) are displayed as “[multiple]”. Check boxes and radio button type parameters are shown with a dash through them.

 

For example: When two cubes of the same height but different length and width are selected, the length and width appear as “[multiple]”. The height displayed is the height of the two objects as they are the same. Changing the value in the length and width parameters will yield two cubes with the same dimensions.

 

A Parameters tab is also available when NURBS curves or surfaces are selected with the Pick tool. The tab displays the NURBS degree, the number of control points, and the closure status. Entering a higher number in the degree field can raise the degree of the curve. This is standard degree elevation without reconstruction. For the surfaces, the NURBS degrees, the number of control points, and the closure status are displayed for both the U and V directions. Entering a higher number in the corresponding degree field can raise the U or V degree of the surface. This again is standard degree elevation without reconstruction.

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