Object construction in interactive mode 

One should to do the following actions to create a new 2delement interactively:
If there are several objects of the selected type that can be created by the users input(s), then the system will show all the possible variants and will wait for the required object to be selecting. The selected new object will be created. For example, in order to construct a crossing point for two lines, one should select on the panel the type of object <Point> and click on the first line in the graphic window, and then repeat this with the second line. The point will be constructed automatically where the two non parallel lines cross, and therefore the system will not request any additional information. A second way to do the same is to switch on the <Intersection point> snap and just to click the left mouse button when the mouse cursor is about the intersection point.
As another example, to construct a circle, that passes through a point and is tangent to two lines, it is necessary to select the type of element being defined <Circle> and in any order select in the graphic window a point and two lines (the <Point> snap musts be switched on). Then select from the offered variants the required circle by clicking on it. After this the defined circle will be constructed and will show up in the elements list.
During construction of this circle a point and two lines were used. Alteration of the geometrical parameters of any of these elements will lead to automatic alteration of the circle. When required, the numeric data for the element being defined should be entered in the appropriate fields in the panel.
When defining objects, the system automatically alters the allowed types of parameters, which can be used for the object definition. The required values can generally be entered in any order. Parameter values can be entered directly or, as a parameter of another object or a collection of parameters of other objects by means of the geometrical calculator. The entered numeric value for a parameter will be set. When entering values via the <Geometrical calculator>, an additional parametric link is created that automatically tracks all alterations of the base elements. Input of numeric values can be performed directly in the parameter values field. For example, the radius of a circle can be assigned directly by entering a numeric value in the <R> field or as the distance from a point to a line using the geometrical calculator. In the first case, the circle radius will not be changed upon altering the other geometrical elements, and in the second, upon changing parameters of the line or the point, the circle radius will be automatically calculated as the current distance between the line and the point. Once all the required data is entered, the new object will be created. If several variants of the new object are possible, then the system offers the user a choice of one of more variants. The object definition process can be ended at any time by clicking the left mouse button within the work area. The object currently being defined will be created (if possible) in the current position.
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