Sketcher is the instrument of building sketch (outline). It allows to input
geometric primitive in CAD-system. The input iz realize with mouse. Clicking
on left mouse button handling as input event. In mouse moving entering object
is redraw, so It allows to control object position before it’s final input.
Clicking on right mouse button handling as cancel event. All current action
stops.

Possible geometric primitives are:

- Point
- Line
- Polyline
- Circle
- Arc
- Bezier curve

Circle input allows as follows:

- By center point & point lying on circle
- By 3 points
- By point and two tangent to curves
- By 2 points & Tangent to curve
- By 3 tangent to curves.

Arc input allows as follows:

- By 3 points
- By center point & 2 limited points
- By 2 points & tangent to line/arc (polilyne mode)

It allows for sketcher to work at polyline mode. At this mode input of line continuously reslize, i.e. end point of first line is start point of second line. At this mode enteiring arc tangent to last entering object.

It allows for sketcher to input objects with snap to existing points/objects.

Snaps:

- End (line/arc)
- Middle (line/arc)
- Center (circle/arc)
- Nearest (point projected on curve)
- Intersection (intersection points of two curves)
- Parallel (input line parallel to existing line)
- Perpendicular (input line perpendicular to existing line)
- Tangent (input geometric primitive tangent to existing object)
- Analyzer ( automatically determine preffered snaps from all )

Sketcher allow to edit entering objects. All properties shows in dialog window.
User can change properties and it’s modify objects and it’s representation.

Entering objects store at object list. It allows to export or import list to
Sketcher.