Is continuously seeding a random number generator performance intensive?

[Jeroen Bollen]

D provides a set of Random Number Generators in std.random. I am 
writing an application which would create a 2D map of noise. To 
do this though, I'll have to calculate the same random numbers 
over and over again. (I cannot store them, that'd take a horrible 
amount of RAM. )

Is it good to re-seed a generator for every coordinate, will this 
be performance intensive? Is there maybe way to easily implement 
Generator.at(uint x) in D?