Contents - Index - Previous - Next
Set Far Objects
Use the toolbar Scene to select objects in the active scene.
Use the toolbar Location to mark the selected object as a "far" object.
Note, the "F" button of the toolbar Location is working together with the "
F" filter of the toolbar Show.
The scene volume calculation and "far" objects
When you create objects or change their dimensions and locations, you do not need to take care how to evaluate the changing scene size, and how to choose the right scale of the scene representation in the 3D view window. The software do it for you automatically. It builds the bounding box that includes all objects of the scene, calculates the appropriate view volume, and adjusts it to the screen dimensions of the 3D view window.
In the simplest case, the scene size, the scene volume, and the view volume mean the same -- they are synonyms. However, sometime you need more complex approach.
In the simplest case, the scene size is defined by the largest object or by the longest distance between the objects. But this rule becomes inconvenient, if you need to consider a "small" object on the background of a "large" object, or a particular "small" object on the background of many other "small" objects (for example, a building on the background of a hill, or a particular building among many other buildings). Although the zoom option partly solve this problem, it would be better to set the size of the exposed part of the scene separately from the actual size of the entire scene. In addition, we would like to avoid the necessity to adjust all the view parameters manually each time, when objects are moving or resizing.
An elegant solution of the described problem is to introduce one more attribute of an object -- the "far" attribute with two possible states ("far" or "near"). Then we can declare some objects as "far" objects (select them in the combo box SCENE, and then mark them with the "F" button of the toolbar Location). The software will exclude them from the scene volume calculation (but not from the view volume calculation). And after that, the parameters of the 3D view will not react on any resizing or moving (or even removing) of "far" objects (the state of the 3D view will depend only on normal "near" objects).
We also need an option to quickly switch this mechanism off without the necessity to revise separately all "far" attributes of the scene objects. This option is represented by "
F" button of the toolbar Show. See the topic Set Scene Show Filters for more details about the three-level system of the appearance filters.
In addition, we need this mechanism to be compatible with the mechanism of the child-parent relationships between objects, that is described in the topic Set Parent Coordinate System. This compatibility is organized as follows. A child object automatically inherits the state of its "far" attribute from its parent object. Therefore, when the selected object is a child of another object, the "F" button of the toolbar Location is disabled (grayed). However, it can be checked (or unchecked), to show that the selected object belongs to the "far" (or "near") object family.
"Far" objects in action
Compare the following two screen shots.
All four pyramids (objects of the type "3D_Cone") are marked as "far" objects by the button "F" of the toolbar Location. Other objects (that constitute the airplane model) are "near" objects.
On the first screen shot, the button "
F" of the toolbar Show is unchecked. Therefore, there is no difference between "far" and "near" objects. All objects together are considered as an entire scene with the diameter of about 2 km. The center of the scene volume is located somewhere between the airplane model and the most far pyramid.
On the second screen shot, the button "
F" of the toolbar Show is checked. Therefore, there is a difference between "far" and "near" objects. And only "near" objects that constitute the airplane model are taken into account for the scene volume calculation. The center of the scene volume is located somewhere inside the airplane model. And pyramids are displayed as a far background of the airplane model.
Note, objects that are marked as "far", but actually are situated near to the scene center (near to other "near" objects) can be partly cut by the near clipping plane of the view volume.