The C interface to the vision library consists of four routines:
VisionOpen, VisionClose, VisionGetErr, and VisionGetObj. Interaction
with the vision server is accomplished by first opening a connection to
with VisionOpen, then using VisionGetObj to request data from the vision
server and finally, when finished, closing the connection to the vision
server with VisionClose.

The vision routines use port identifiers to maintain connections to
the vision server. By using this system a single C program would be
able to make connections to multiple vision servers or to make multiple
connections to a single vision server. Each time a connection to a vision
server is opened with the VisionOpen command it should later be closed
with the VisionClose command.


int VisionOpen(char *Addr)
    Open a connection to a vision server on the machine with the specified
IP address. Addr is a character string of the IP address of a machine
that is running a vision server. On success, a valid file descriptor
is returned.  This file descriptor should be used for all future access
to the vision server. On failure -1 is returned and VisionGetErr should
be used to retrieve an error message.

void VisionClose(int fd)
   Close a connection to the vision server. fd is the descriptor
returned by a successful call to VisionOpen.

int VisionGetObj(
   int fd,       // File Descriptor to use 
   char *ObjId,  // The ID of the object to retrieve from the vision server 
   unsigned *x,  // x coordinate 1 (Center for circle) 
   unsigned *y,  // y coordinate 1 (Center for circle) 
   unsigned *x2, // Width 
   unsigned *y2  // Height )
   Get information about a specific object currently defined on the vision
server. fd is a descriptor returned by a successful call to VisionOpen.
ObjId is the character Id of the object for which information is being
requested. The object must be defined on the vision server and should
either be a Circle, a Rectangle, or a Line.. x, y, x2, and y2 are pointers
to variables to store information from the vision server. The meaning of
each is dependent on the particular type of object for which information
is being requested:

                 x                   y             x2               y2
Rectangle x coord of corner   y coord of corner   width            height
Circle    x coord of center   y coord of center   radius           radius
Line      x coord of start    y coord of start  x coord of end  y coord of end

A return value of 0 indicates success and a return value of -1 indicates
an error.

char *VisionGetErr()
    Get a text message indicating the last error from the vision server.
VisionGetErr should be used immediately after an error to retrieve an
error message and should be ignored otherwise.