Checks in the global variable "point values" to see if the exact data point being requested has already been asked for and returns the value if it's already saved.
npn_check_point_cached(layer, lat, long, date)The numeric value of the cell located at the specified coordinates
and date if the value has been queried, otherwise NULL.
The name of the queried layer.
The latitude of the queried point.
The longitude of the queried point.
The queried date.