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Convert vertical datum in CC
Posted: Thu Jun 29, 2023 4:00 pm
by 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!
Re: Convert vertical datum in CC
Posted: Sun Jul 02, 2023 6:29 pm
by daniel
Sadly, CC does not handle coordinate systems... Maybe the GDAL and PDAL suites might help you?
Re: Convert vertical datum in CC
Posted: Sun Jul 02, 2023 9:43 pm
by DA523
Sadly, CC does not handle coordinate systems..
What about UTM coordinates cc handling.?
Re: Convert vertical datum in CC
Posted: Mon Jul 03, 2023 7:36 am
by daniel
What do you mean?
Re: Convert vertical datum in CC
Posted: Wed Jul 05, 2023 1:54 pm
by Liang
Hi Daniel,
Thanks for the reply!
Eventually, I decided to convert my reference data from EGM2008 to ellipsoid using gdal
Re: Convert vertical datum in CC
Posted: Tue Jul 25, 2023 10:17 pm
by DA523
by daniel ยป 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
Re: Convert vertical datum in CC
Posted: Fri Jul 28, 2023 9:55 pm
by 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 ?
.
Re: Convert vertical datum in CC
Posted: Fri Jul 28, 2023 10:20 pm
by DA523
attached 3D pointscloud example
.
- Screenshot (146).png (79.51 KiB) Viewed 7788 times
..
check CC file below
Re: Convert vertical datum in CC
Posted: Tue Aug 08, 2023 9:12 pm
by 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 ?
Re: Convert vertical datum in CC
Posted: Wed Aug 16, 2023 1:43 pm
by daniel
GDAL would be my default guess but mainly because that's the only package I know :D