Algorithms for Object Selection in GIS

Algorithms for the selection of point,line and polygon are studied respectively in this paper. In the selection of a point,absolute distance between two points are used instead of the commonly used square root distance,and higher efficiency is achieved.For the selection of a line,a new distance between a point and a curve is defined,and higher efficiency is also achieved.In order to raise the efficiency of polygon selection,some improvements have been made to the“semiline”method which is used to judge whether a point is inside a polygon,and a new algorithm which needs less computation.