Calculating a Function out of a cloud of points

Hallo,

i have a Problem i need to solve fast :-(

Problem:

Density is a function of pressure and temperature

I can create a cloud of points for the density:

                         Temperature

Pressure                 100°          200°          300°  

      100bar           Density      Density

     200 bar

     300 bar

          etc                  

My problem is now, how can i calculate a Density Function depending on these Input Points?

Can anyone help me ?

Thx =)