> For the complete documentation index, see [llms.txt](https://docs.jakarto.com/guide-data-downloader/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.jakarto.com/guide-data-downloader/fr/selection-des-donnees/choix-du-systeme-de-coordonnees.md).

# Choix du système de coordonnées

Par défaut, les téléchargements utilisent le SCR source (généralement une zone MTM CSRS en horizontal et CGVD2013 en vertical).

Vous pouvez modifier séparément les SCR horizontal et vertical. Les listes proposées sont limitées à l’intersection des transformations autorisées pour tous les fichiers actuellement sélectionnés.

Notes :

* Toute modification du SCR horizontal et/ou vertical entraîne une reprojection à la volée.
* Toute reprojection produit un fichier **LAS** ; sans reprojection et si **LAZ** est préféré, l’outil livre le **COPC (.laz)** d’origine.


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# Agent Instructions
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## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.jakarto.com/guide-data-downloader/fr/selection-des-donnees/choix-du-systeme-de-coordonnees.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.