topic Re: Re-projecting XYZ Values in Coordinate Reference Systems Questions

Re-projecting XYZ Values

SeanMcDade — Thu, 11 Sep 2014 13:49:01 GMT

Hi,

I have a question relating to converting XYZ values from one projection system to another.

If I have a grid of XYZ points in one projection system where

X = Easting

Y = Northing

Z = Elevation

and I convert them to another projection system, should my Z values change as well as my X and Y values or should they stay the same? It seems to me that the Z values should stay the same but I could be wrong.

Thanks,

Sean.

Re: Re-projecting XYZ Values

MelitaKennedy — Thu, 11 Sep 2014 18:04:34 GMT

Currently they will stay the same because we aren't projecting vertical data yet. Even when we do, as long as the vertical coordinate system stays the same, the Z values should be unchanged.

Melita

Re: Re-projecting XYZ Values

Mohamed_MagdyMohamed_Hussain — Sat, 13 Sep 2014 00:05:40 GMT

That is depend on the transformation parameters you used. usually there are three parameter for transformation called translation parameters (X, Y, Z) if Z have value there are different in Z will be observe but if delta Z is 0 there are no change in Z Value.

But there are another case if the transformation parameters are 7 parameters as:

- 3 parameters translation (dX, dY, dZ)

- 3 parameters rotation (rX, rY, rZ)

- 1 parameter for Scale factor

in this case with 7 parameters the Z value must be changed even dZ is zero

all above for ellipsoidal elevation which observed directly by GPS or ASTER, STRM DEM and that is different about the MSL (Mean Sea Level) elevation

Thanks,

Mohamed