trouble understanding coordinate values

[esovetkin]

Hi, I have trouble understanding coordinate system values. My original data comes in citygml format, which I transform to cityjson file using citygml-tools, and then to an obj file using cjio library.

However, during one of the steps my second coordinate value changes its range.

Here is an example of citygml file:

> cat ex.gml
...
 <gml:posList srsDimension="3">280962.724 5657686.942 38.017 ...
...

that has coordinates in epsg:25832.

citygml-tools generates cityjson file, that has seemingly correct coordinate system:

> cat ex.json
...
"geographicalExtent": [
       280000,
       5657000,
       0,
       281000,
       5658000,
       50.072
     ],
     "referenceSystem": "https://www.opengis.net/def/crs/EPSG/0/25832"
...

However, if I export cityjson to an obj file, or use cjio to work with geometries, the second coordinate changes its range from "5658*" to "9167*"

cat ex.obj
 v 280962.724 9167323.573 42.436
 v 280971.022 9167319.498 42.436
 v 280973.051 9167323.645 47.246
...

I have trouble understanding why this happens, and I would like to keep by coordinate system intact.

[esovetkin]

Ah, I understood that the way coordinates are stored does not equal the actual values of the coordinates (despite visual similarities).

https://cjio.readthedocs.io/en/latest/api_tutorial_basics.html#Geometry-boundaries-and-Semantic-Surfaces

This explains how to get the original coordinates.

[kenohori]

Also see: https://www.cityjson.org/dev/realcoords/