Esri TIN

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Esri TIN is a proprietary geospatial data format used to store elevation data as a triangulated irregular network (TIN). It was introduced with Esri’s ArcView GIS and is still used in ArcGIS products.

How Esri TIN data is stored
- A TIN is kept as a set of binary files in one folder, all using the .adf extension. Most of these files are required, and some are optional.
- Key files (mandatory):
- tnxy.adf — stores the X and Y coordinates for every point in the TIN.
- tnz.adf — stores the Z (height) for each point, aligned with tnxy.adf.
- tnod.adf — lists the three point indices that form each triangle.
- tedg.adf — contains the topology of triangles and the type of their edges.
- thul.adf — describes the hull (outer boundary) and any holes in the TIN.
- tdenv.adf — header and basic statistics (counts of points, triangles, etc.).
- tmsk.adf — a mask that marks which triangles are visible or hidden.
- tmsx.adf — index file for the mask.
- Optional files (may be present if needed):
- prj.adf — coordinate system and projection information.
- tnval.adf — data about tags assigned to certain points.
- tndsc.adf — statistics about point tags.
- ttval.adf / ttdsc.adf — triangle tag data.
- ArcGIS 10 introduced changes and two new files:
- teval.dbf and tnodinfo.dbf (used for breaking edges and point information).
- Some encoding rules for breaking edges also changed in tedg.adf.

Core ideas you should know
- Points, triangles, and edges: tnxy.adf and tnz.adf define 3D points; tnod.adf lists triangles by referencing those points; tedg.adf describes how triangles share edges.
- Supersized points: Superpoints are extra points added during triangulation to help shape the surface (often four points around the main data). They’re usually the first points in tnxy.adf and tnz.adf and are typically masked in tmsk.adf.
- Hulls and holes: thul.adf defines the outer boundary and any holes in the TIN, so the network can model complex shapes like islands or lakes.
- Masking: tmsk.adf uses a bit mask to hide or show triangles, which is useful for terrain holes or areas outside the boundary.
- Endianness: The binary files use specific byte orders (big-endian or little-endian). Reading them correctly requires appropriate software.

Overview in plain terms
Esri TIN is a multi-file binary format Esri uses to store a 3D surface made of triangles. It keeps a separate file for points (coordinates), a file for how those points form triangles, a file for how triangles connect to each other, and supporting files for the surface boundary, visibility, coordinate system, and optional data tags. ArcGIS may add or modify several of these files, especially when updating from older to newer versions.

Why it matters
- It’s a compact, organized way to store elevation data and complex surface features (like edges and holes) for GIS applications.
- Because it’s proprietary, software from Esri and some open tools can read it, but exact compatibility can depend on the ArcGIS version and file set.

In short: Esri TIN compresses a 3D terrain into several coordinated binary files that describe points, triangles, edges, boundaries, visibility, and optional tag data, all designed to work together in ArcGIS and related GIS tools.