If your data is in a matrix of dimensions [samples x 3], e.g.
data=[lon1 lat1 value1;
lon2 lat2 value2;
lon3 lat3 value3;
lon4 lat4 value4;
then you simply need to do
mean(data) and that will calculate the mean of each column.
Hope this solves your question. If yes, please accept the answer, if not, let me know.