I am very new to GNUplot. please help me : I have a file with three columns. All three have different values. To plot it in a smooth surface with a color gradient for third column what should I do? 
the data file is look like follows:

1431.564087	-556.7048268	-14.09538931
1445.544205	-562.1413974	0
1445.544205	-562.1413974	-6.577848346
1452.06826	-564.6784636	6.577848346
1445.544205	-562.1413974	-6.577848346
1452.06826	-564.6784636	9.396926208
1442.748182	-561.0540833	-1.879385242
1444.612197	-561.7789593	11.27631145
1433.428103	-557.4297029	-4.698463104
1438.088142	-559.2418931	4.698463104
1433.428103	-557.4297029	0
1433.428103	-557.4297029	0.939692621
1432.496095	-557.0672648	-0.939692621
1433.428103	-557.4297029	0
1433.428103	-557.4297029	-2.819077862
1436.224127	-558.517017	-1.879385242
1438.088142	-559.2418931	0
1438.088142	-559.2418931	0
1438.088142	-559.2418931	0
1438.088142	-559.2418931	6.577848346
