ECEF data in quantized mesh tiles could not match the latitude/longitude calculated from tile x/y

Quing_in_Vancouver · July 30, 2021, 11:45am

for example,
we took tile (column 850, row 600, zoom 10) which is longitude 118.828, latitude 29.5352.
in quantized mesh tiles, we got
centerX=5295633.3156387117
centerY=-3119125.5139920237
centerZ=1699514.1494967942
it looks like a valid ecef value near surface of earth, and convert to LLA is
Latitude : 15.55665 deg N
Longitude : 329.50194 deg E
Height : -11.1 m

it’s far from the tile’sLLA.
What did we miss in calculation?

another example data we found also doesnt match GitHub - bertt/quantized-mesh-tile-cs: A .NET Standard 2.0 library for decoding a quantized mesh tile into vertices
Terrain.Tiles.Tests.data.9_533_383.terrain, doesnt match centerXYZ
CenterX == 4492197.38443436
CenterY == 596134.0874495716
CenterZ == 4473851.280340988

is centerX,Y,Z ECEF? how to convert them to longitude, latitude correctly.

Quing_in_Vancouver · July 31, 2021, 6:16am

following tilexyzoom to LLA formulas in

github.com

loicgasser/quantized-mesh-tile/blob/master/quantized_mesh_tile/global_geodetic.py

""" This module defines the :class:`quantized_mesh_tile.global_geodetic.GlobalGeodetic`.
Initial code from:
https://svn.osgeo.org/gdal/trunk/gdal/swig/python/scripts/gdal2tiles.py
Functions necessary for generation of global tiles in Plate Carre projection,
EPSG:4326, unprojected profile.
Pixel and tile coordinates are in TMS notation (origin [0,0] in bottom-left).
What coordinate conversions do we need for TMS Global Geodetic tiles?
Global Geodetic tiles are using geodetic coordinates (latitude,longitude)
directly as planar coordinates XY (it is also called Unprojected or Plate
Carre). We need only scaling to pixel pyramid and cutting to tiles.
Pyramid has on top level two tiles, so it is not square but rectangle.
Area [-180,-90,180,90] is scaled to 512x256 pixels.
TMS has coordinate origin (for pixels and tiles) in bottom-left corner.

Reference
---------
"""
import math

MAXZOOMLEVEL = 32

This file has been truncated. show original

everything looks perfect now

sam.rothstein · August 2, 2021, 12:42am

@Quing_in_Vancouver

Welcome to the community I am happy to hear that you were able to resolve your issue. Thank you for posting your solution in this thread - I will refer other community members to this post if similar issues arise.

Best,
Sam