The paper considers the piecewise linear interpolation of Gaussian processes with continuous sample paths and stationary increments. The interrelation between the smoothness of the incremental variance function, d(t-s)=E[(X(t)-X(s))2], and the interpolation errors in mean square and uniform metrics is studied. The method of investigation can also be applied to the analysis of different methods of interpolation. It is based on some limit results for large deviations of a sequence of Gaussian non-stationary processes and related point processes. Non-stationarity in our case means mainly the local stationary condition for the sequence of correlation functions rn(t,s), n=1,2,...,which has to hold uniformly in n. Finally, it discusses some examples and an application to the calculation of the distribution function of the maximum of a continuous Gaussian process with a given precision.