WTML File

What are WTML files and how to open them

Are you having problems opening a WTML file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your WTML files.

What is a WTML file?

A .WTML file is a WorldWide Telescope Collection file.

WorldWide Telescope Collection (.WTML) files are XML‐based "collection" files used by the WorldWide Telescope software to describe groups of astronomical or Earth imagery, observational data, panoramas, tours, places, studies, or surveys. They are created by WorldWide Telescope (originally by Microsoft Research, now under the American Astronomical Society) to define metadata for how to display and organize various image or dataset resources within its virtual sky/Earth interface. A .WTML file tells the program what images exist where, how they are grouped, how to view them, what thumbnails to show, and what kinds of data (e.g. studies, tours, links) are included.

WTML files are typically produced via WorldWide Telescope's tools or SDKs that prepare sky survey image‐tiles or other image sets. For example, the Study Chopper converts a large image into a pyramid of tiles at multiple zoom levels and then generates a corresponding .WTML file referencing those tiles, along with thumbnail, credits, and viewing metadata so WorldWide Telescope can load them correctly. WTML files are editable by users or developers who want to assemble or share custom collections ("payloads" or "communities") that combine folders of studies, surveys, tours, places, or links.

Technically, a .WTML file always begins with an XML declaration (for example <?xml version="1.0"?>) and contains a hierarchy of <Folder> elements. Within those, entries like <Place>, <ImageSet>, <Tour>, <ForegroundImageSet> etc define the types of items in the collection. Keywords such as Name, Thumbnail, Url, DataSetType, TileLevels, Projection, and BaseTileLevel configure how images are loaded, projected, and displayed. Presence of strings like "THUMBNAIL", "PLANET", "SEARCH", "GROUP" etc helps recognize such files.

How to open WTML files

We have identified one WTML opener that is compatible with this specific type of WTML file.

Programs that open WorldWide Telescope Collection files

Last updated: August 14, 2026

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