翻译：A trivial approach for the selection mechanism consists of
checking for the inclusion of selection points coordinates in
each objects’ area. Even with a linear complexity, processing
2,500,682 objects involve a large number of computations. A
pixel is selected by pointing to it with the mouse on the
screen. To determine the object(s) to select, a projection of
the coordinates of the selected pixel must be performed in the
OpenGL 3D space [4] (Fig. 4). This operation produces in a
straight line along the Z axis. Once the projection line is
known, it is possible to compute the intersection between this
line and the objects present in the OpenGL scene. If an
intersection is detected, it means that the object involved is
pointed to and should therefore be selected. To accelerate this
step, some objects could be indexed by the areas they cover.
In that case, the selection is faster, but memory consumption
increases with the index size. 