persp fail with non-equidistant dates

Hello,
when I plotted non-equidistant data in 3D (using persp and contour), it
was ended with the same error message:

persp(y, x, z, xlab="latitude", ylab="longitude", zlab="altiude",

main="Altitude")
Error in persp.default(y, x, z, xlab = "latitude", ylab = "longitude",  :
  increasing 'x' and 'y' values expected

How to fix it? The original data are in columns

 50.84925    14.65715 614.0  48909.14   -62.49  99  48929  5  122306
 50.84919    14.65702 617.0  48816.32  -145.82  69  48836  6  122331
 50.84908    14.65681 622.0  49113.40     6.64  99  49133  4  122442

Tomas Bayer
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