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Coordinate systems do not match #633

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anawas opened this issue Nov 26, 2024 · 3 comments
Open

Coordinate systems do not match #633

anawas opened this issue Nov 26, 2024 · 3 comments
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bug Something isn't working prio-med Medium priority

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@anawas
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anawas commented Nov 26, 2024

Summary

The ALMA observatory (Atacama Large Millimeter/submillimeter Array) can work in different configurations. For most of them there are OSKAR .tm-files available in Karabo. If one plots the configuration of, say version 'cycle 8.10' and 'out 09' with karabo the coordinates of the stations differ significantly (see picture). I reckon that the coordinates in image 'ALMA Version Cycle 8.10' are correct. But the ones in the image on the right hand side are not. The centre is much too far away from the stations.
Präsentation1

Steps to reproduce

Run the follwing script and compare the output images:

from karabo.simulation.telescope import Telescope, ALMAVersions

site_name = "ALMA"
instrument_versions = [ALMAVersions.CYCLE_8_10, ALMAVersions.OUT_09]
for version in instrument_versions:
    alma_site = Telescope.constructor(site_name, version=version)
    alma_site.plot_telescope(f"{site_name}.{version.value}.png")

Expected result

The coordinate range of both images should be alike.
@anawas anawas added bug Something isn't working prio-med Medium priority labels Nov 26, 2024
@anawas anawas self-assigned this Nov 26, 2024
@anawas
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anawas commented Nov 26, 2024 •
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Possible cause

I looked at the .tm-folders in karabo/data. It seems that the layout data has different units.
For alma.cycle8.10.tm/layout.txt one finds:

-1.137979806999999937e+03 9.995963548000000642e+00
3.863476964999999836e+02 -1.962095364999999902e+03
4.482469952999999805e+02 6.461269628000000012e+02
-1.275851495000000114e+03 -1.433665864999999940e+03
1.241720548999999892e+03 -1.079905150999999933e+03
...

I assume this is in metres from centre. For alma.out09.tm/layout.txt there is

6.277898100000000559e+05 7.453079620000000112e+06
6.278013100000000559e+05 7.453100269999999553e+06
6.278142600000000093e+05 7.453128290000000037e+06
6.278603100000000559e+05 7.453071139999999665e+06
6.278348499999999767e+05 7.453132370000000112e+06
...

This looks like geocentric coordinates.

@anawas anawas mentioned this issue Nov 26, 2024
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mpluess commented Nov 28, 2024

Nice find. Here are all details about the OSKAR telescope model format, might be helpful: https://ska-telescope.gitlab.io/sim/oskar/telescope_model/telescope_model.html

@anawas
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anawas commented Dec 3, 2024

The coordinates seem not to be geocentric ones. Converting them to geodesics point to locations that are not in the vincinity of the observatory.
The files in question were added 2 years ago. Unfortunately, I cannot find a reference to where the data comes from. Does anybody have an idea where they were found?

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