# Correlation and terrain databases [duplicate]

This question already has an answer here:

I would like to know what kind of computation I could perform on a terrain database.
I'm making terrain for VBS2 from raw data (shp files and DTM Elevation files) and then I'd like to be able to check correlation between these two terrain. I want to check that VBS2 created terrain is ''enough'' correlated with the previous data.
I planned to check the shp files and DTM files of course.
But I was wondering if there is mean, median or coefficient that I could calculate on the terrain. Moreover, should I grid the terrain and analyze each square? Thanks

## marked as duplicate by Mapperz♦Apr 9 '13 at 1:06

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## 1 Answer

First of all correlation is `the degree to which two or more attributes or measurements on the same group of elements show a tendency to vary together`.

I think what you're looking for is the RMSE between your datasets.

From wikipedia:

``````The root-mean-square deviation (RMSD) or root-mean-square error (RMSE) is a frequently
used measure of the differences between values predicted by a model or an estimator and the
values actually observed. These individual differences are called residuals when the calculations
are performed over the data sample that was used for estimation, and are called prediction errors
when computed out-of-sample. The RMSD serves to aggregate the magnitudes of the errors in predictions
for various times into a single measure of predictive power. RMSD is a good measure of
accuracy, but only to compare forecasting errors of different models for a particular variable
and not between variables, as it is scale-dependent.
``````

and the formula to calculate the RMSE is: where n is your sample, Yt is your original values Yt_hat is the predicted values. Lower RSME values are better.

• also read this paper - it compares correlated terrain generated with different engines. – nickves Apr 8 '13 at 13:00