Convert vertical datum in CC

[Liang]

Hi,

I'm interested in using CloudCompare to validate my glacier's 3D models in point cloud (PC) format. The vertical datum of my models is WGS84 ellipsoid, but the reference PC (which I converted from a DEM to a point cloud) is in EGM2008 orthometric/geoid height. I'm wondering if there is a way to convert the PC's vertical datum from WGS84 ellipsoidal height to EGM2008 orthometric/geoid height.

I believe it might involve using a transformation matrix, but I'm not sure how to calculate the matrix. If anyone has insights or suggestions on this matter, I would greatly appreciate it!

Thank you in advance for your assistance!

[daniel]

Sadly, CC does not handle coordinate systems... Maybe the GDAL and PDAL suites might help you?

[DA523]

Sadly, CC does not handle coordinate systems..

What about UTM coordinates cc handling.?

[daniel]

What do you mean?

[Liang]

Hi Daniel,
Thanks for the reply!
Eventually, I decided to convert my reference data from EGM2008 to ellipsoid using gdal

[DA523]

by daniel » Mon Jul 03, 2023 10:36 am
What do you mean?

If we open UTM xyz , CC uses cartesian coordinates while UTM has curved Z reference axis (sea level) (earth curvature)
I sent you an email containing python code to prepare UTM coordinates to CC and reflect real shape
I hope you can check it

[DA523]

What do you mean?

Suppose a ship travels inline with equator for a distance of 10000 km (earth circumference/4).
If z=0 y=0 and x from 0 to 10000 km
GPS coordinates are xyz in meters( UTM) and z is referenced to sea level which the same of earth curvature
CC represents track in straight line not curve
Can GDAL or other software prepare UTM to be represented in CC in real shape ?



.

[DA523]

attached 3D pointscloud example
.

Screenshot (146).png (79.51 KiB) Viewed 7793 times

..
check CC file below

2500km.zip

(246.59 KiB) Downloaded 808 times

[DA523]

Let have these UTM coordinates (xyz in m) from a ship GPS log

x,y,z

468286,4082477,0
467995,3981250,0
467704,3880024,0
467413,3778797,0
467121,3677571,0
466830,3576345,0
466539,3475118,0
466248,3373892,0
465957,3272665,0
465665,3171439,0
465374,3070213,0
465083,2968986,0
464792,2867760,0
464501,2766533,0
464209,2665307,0
463918,2564081,0
463627,2462854,0
463336,2361628,0
463044,2260401,0
462753,2159175,0
462462,2057949,0

The real shape of ship track is ARC not straight line because earth curvature
GPS use z referenced to sea level (curved )
Because CC uses Cartesian coordinates ,it shows as straight line not curve line
Is there any existing software,lib which prepares utm to Cartesian so CC can show real curved line ? GDAL ?

[daniel]

GDAL would be my default guess but mainly because that's the only package I know :D