The paper introduced the outline of Chinese geocoordinate system and determination principles of engineering control network coordinate system and also introduced the methods of selection and decision of central meridian and projection plane of engineering control network.

The cylinder boxes for the subassemblies of each instrument are set up,and the early warning algorithm for collision of the instruments based on the projection plane is proposed according to the theory that the axes of the two boxes have the common perpendicular line.

This paper discusses the influence of height varying in the projection surface of terrestrial network when applying results of hugh accuracy positioning by satellite observations to Gauss coordinate system.

In order to transform GPS networks to independent coordinate system strictly, this paper puts forward a new method, by which the regional ellipsoidal surface is more coincidental with the projection surface by means of readjusting orientation of ellipsoid ,the effectiveness of this method has been demonstrated by the application to Ningbo GPS control network.

From the beginning with changing the central meridian line and the projective plane, the paper analyzes the selection of the coordinate system of the plane control network in shijiazhuang city.

Based on inclusion exclusion principle of set theory,a new algorithm to calculate the whole projective area was put forward to those overlapped complex geometrical objects in any direction.

It introduces the concept of 揷oefficient of the resultant forces and gives the exact solution to the projection area in the direction of the resultant forces.

Effective area of shining light on crown,crown ratio and projection area of crown of E.