A camera system comprising a camera, a monitor, an image detector, a touch screen, and a remote control. The present invention also provides a method of preparing a proppant material by heating a reaction mixture comprising a plurality of oxides and one or more additives in a reactive atmosphere to a temperature below the melting point of the reaction mixture to form a powder including one or more reaction products, and then processing the powder to form spherical particles. An optimal concentration for the first target may be obtained based on the expected value. The opening has an angled sliding surface, and the end of the floating pin away from the head is connected to the suction cup, and an axial and radial movement of the floating pin adjusts relative position of the suction cup and the positioning post for aligning the positioning post and the pinhole. The retrieved symbol is emitted to a literal stream if the current context is a root context, where the code stream and the literal stream are to be compressed and decoded by a decoder.