Esri TIN

Esri TIN
Filename extensions .adf
Developed by Esri
Type of format GIS

The Esri TIN format is a popular yet proprietary geospatial vector data format for geographic information system (GIS) software for storing elevation data as a triangulated irregular network. It is developed and regulated by Esri. The Esri TIN format can spatially describe elevation information including breaking edge features. Each points and triangle can carry a tag information.[1] [2] A TIN stored in this file format can have any shape, cover multiple regions (e.g. islands) and contain holes (e.g. lakes).[3]

In 2007 a reverse-engineered description of Esri TIN format came to light.[4] Since then, the Virtual Terrain Project, an open-source software, has implemented support for reading the format, without the need of ArcGIS being installed.[5]

Overview

The Esri TIN format is a digital vector storage format for storing elevation information including breaking edge features. The Esri TIN format was introduced with ArcView GIS.

The Esri TIN format consists of a collection of files with specific filenames and a common filename extension, stored in the same directory. Most of the files are mandatory files (tdenv.adf, tedg.adf, thul.adf, tmsk.adf, tmsx.adf, tnod.adf,[5] tnxy.adf[5] and tnz.adf[5]), optionally a file containing the coordinate system and projection information (prj.adf) and files containing point tag information (tnval.adf and tndsc.adf) and triangle tag information (ttval.adf and ttdsc.adf)[1][2] can be given.

Mandatory files 

The endianness of most of the files is big-endian. tmsk.adf, tmsx.adf and tdenv.adf have mixed endianness.

Other files 

The endianness of the file tndsc.adf and tnval.adf is little-endian.

Files generated by ArcGIS 10 
Size of file

A TIN with n points (incl. superpoints) and k triangles, the file sizes calculate to:

Mandatory files

tnxy.adf - X and Y coordinates of the points of the TIN

Contains and array of X and Y coordinate values, one pair for each point of the TIN. The data set for each point can be described by the following structure:

Bytes Type Endianness Usage
0–7 double big X coordinate value
8–15 double big Y coordinate value

tnz.adf - Z coordinates of the points of the TIN

Contains an array of Z coordinate values, one for each point of the TIN. The values are in same order as the values in tnxy.adf and together store the 3 dimensional coordinate of each point of the TIN. The data set for each point can be described by the following structure:

Bytes Type Endianness Usage
0–3 float big Z coordinate value

tnod.adf - Indices of the points that form the trianlges of the TIN

Contains an array of indices to the points that form the triangles of the TIN, 3 indices for each triangle. The indices are in the range of 1 to the number of points ([1, # of points]). The front face of a triangle (usually the upper side) is that face, that has the 3 points/corners ordered clockwise when viewed. The data set for each triangle can be described by the following structure:

Bytes Type Endianness Usage
0–3 int32 big Index of the first point of a triangle
4–7 int32 big Index of the second point of a triangle
8–11 int32 big Index of the third point of a triangle

tedg.adf - Topology of the triangles and the type of its edges

Contains information about the topology of the triangles and the type of their edges.

There is an entry for each triangle with each 3 indices, that point to the position (number of the index) in tnod.adf file to identify the triangle, that shares an edge with the triangle described by the current data set, and the point of that triangle, that form that edge.

For each triangle in tnod.adf exists a data set at the same file location in tedg.adf. Each of the values point to the location in tnod.adf, where the point is specified (the index of that point) that form an edge. At the same time, since the location in tnod.adf and tedg.adf correspond, each of the values point to the location in tedg.adf, where the location of the value is specified. Rule: If edge a of triangle A points to edge b of triangle B, then edge b of triangle B must point to edge a of triangle A. Since edge definition in tedg.adf and point definition in tnod.adf of each triangle are at the same location the files, the indices in tedg.adf point to the point definition in tnod.adf of the neighbouring triangles.

The indices encode the actual index and type of the edge. The actual indices are not file offsets in bytes, but rather in int32 values, in the range of 1 to the number of points ([1, # of points]). If the value is negative (bit 31 is set) the edge is a breaking edge. Furthermore, bit 30 of the int32 values is used to determine if the edge is a hard or soft breaking edge. If the actual index would be 1234 (0x000004D2) then a hard breaking edge would be encoded as -1234 (0xFFFFFB2E) and a soft breaking edge as -1073743058 (0xBFFFB2E). The edge definition of the neighbouring triangle must mirror the edge type. ATTENTION: This behaviour has changed since ArcGIS 10. Please compare with the information given in section 'Format changes and files new with ArcGIS 10'.

The data set for each triangle can be described by the following structure:

Bytes Type Endianness Usage
0–3 int32 big Encoded index of point definition (index of a point) of the neighbouring triangle in tnod.adf that form an edge with the first point of the triangle
4–7 int32 big Encoded index of point definition (index of a point) of the neighbouring triangle in tnod.adf that form an edge with the second point of the triangle
8–11 int32 big Encoded index of point definition (index of a point) of the neighbouring triangle in tnod.adf that form an edge with the third point the a triangle

tdenv.adf - Header or statistics

This file contains information that could be seen as a mix of file header and statistic data.

Bytes Type Endianness Usage
0–3 int32 big Number of points (regular points and superpoints)
4–7 int32 big Number of triangles
8–11 int32 big Number of indices and separators in thul.adf
12–15 int32 big 0 (in version 9) / number of breaking edge entries in teval.adf (version 10)
16–19 int32 big Number of triangles, not masked in tmsk.adf
20–23 int32 big Number of regular points
24–27 int32 big Number of superpoints
28–31 float big Minimum height (Z value of the lowest point; zmin)
32–35 float big Maximum height (Z value of the highest point; zmax)
36–39 int32 ? big Unknown, different values encountered
40–47 double big Minimum extent in X direction (xmin)
48–55 double big Minimum extent in Y direction (ymin)
56–63 double big Maximum extent in X direction (xmax)
64–71 double big Maximum extent in Y direction (ymax)
72–79 double ? big Unknown, always 0
80–87 double ? big Unknown, different values encountered
88–91 int32 big Unknown, always 70001 (version 9) / 90001 (version 10); maybe a version number
92–95 int32 little Number of used tags (incl. tag 0 for superpoints)
96–99 int32 ? big Unknown, always 0; maybe unused
100–103 int32 ? big Unknown, always 0; maybe unused

thul.adf - Hull, bounding polygon and holes

Contains an array of indices and separators, that defines the outer boundary of the TIN and its holes. The indices are in the range of 1 to the number of points ([1, # of points]). The separators are -1 (0xFFFFFFFF) and zero (0).

If the TIN is constructed using superpoints (usually the first 4 points), thul.adf lists the indices of these points and then -1 (0xFFFFFFFF). After the separator follows one or more lists of indices that form bounding polygons (outer boundaries) and maybe holes (inner boundaries). These lists are separated by zero (0) values.

If the TIN does not contain superpoints, thul.adf starts with the -1 (0xFFFFFFFF) separator, which is followed by one or more lists of indices that form bounding polygons (outer boundaries) and maybe holes (inner boundaries). These lists are separated by zero (0) values.

The indices and separators are 4 byte integer values (int32), stored in big-endian byte order.

tmsk.adf - Mask

Contains an array of bits (stored in 4 byte integers) that specify the visibility of the triangles of the TIN. This can be used to hide the triangles inside of terrain holes or outside the terrain (outside the outer boundaries).

The file is stored using the same structures (header and records) as a shapefile, but since it only stores the visibility values of the triangles many fields of the header are used.

The file header is fixed at 100 bytes in length and contains 17 fields; nine 4-byte (32-bit signed integer or int32) integer fields followed by eight 8-byte (double) signed floating point fields:

Bytes Type Endianness Usage
0–3 int32 big File code (always hex value 0x0000270a)
4–23 int32 big Unused; five uint32
24–27 int32 big File length (in 16-bit words, including the header)
28–31 int32 little Version 0 ; probably unused
32–35 int32 little Shape type 0 ; probably unused
36–43 double little Minimum X extent (always 0.0) ; unused
44–51 double little Minimum Y extent (always 0.0) ; unused
52–59 double little Maximum X extent (always 0.0) ; unused
60–67 double little Maximum Y extent (always 0.0) ; unused
68–75 double little Minimum Z extent (always 0.0) ; unused
76–83 double little Maximum Z extent (always 0.0) ; unused
84–91 double little Minimum M extent (always 0.0) ; unused
92–99 double little Maximum M extent (always 0.0) ; unused

The file then contains at least 2 records. Each record is prefixed with a record-header of 8 bytes:

Bytes Type Endianness Usage
0–3 int32 big Record number (1-based)
4–7 int32 big Record length (in 16-bit words)

Following the record header is the actual data.

Record 1: The data of record number 1 is 2 word long and contains only the size of the data of record number 2 in 4 byte integers, stored as 4 byte integer (big-endian) itself.

Record 2: The data of record number 2 contain the following variable length structure:

Bytes Type Endianness Usage
0–3 int32 big Number of integer in the mask array
4–7 int32 big Unused; always 0; maybe an offset (bits, bytes or integers?) into the mask array, where the actual mask bits start
8–11 int32 big Number of used bits in the mask array
12– uint32[] big Mask array

Bit 0 (least significant bit) of the first integer contains the visibility flag (invisible if set to 1) of the first triangle defined in tnod.adf. Bit 1 of the first integer contains the visibility flag (invisible if set to 1) of the second triangle, and so on. All 32 bits of the integers get used (no sign bit).

Record 0: Records with the record number 0 must be ignored.

tmsx.adf - Index file for the mask

The index file contains the same 100-byte header as the tmsk.adf file, followed by any number of 8-byte fixed-length records which consist of the following two fields:

Bytes Type Endianness Usage
0–3 int32 big Record offset (in 16-bit words)
4–7 int32 big Record length (in 16-bit words)

Using this index, it is possible to seek backwards in the tmsk.adf file by, first, seeking backwards in the index (which is possible because it uses fixed-length records), then reading the record offset, and using that offset to seek to the correct position in the tmsk.adf file. It is also possible to seek forwards an arbitrary number of records using the same method.

Optional files

Depending of the information stored in the TIN, some extra files are needed.

prj.abf - Projection and CRS

Contains the coordinate system and projection information. The file can be either in the Esri flavour of the well-known text format (WKT), a simple keyword-value notation (Keyword: Projection, Datum, Spheroid, Units, Zunits, Xshift, Yshift, Zone,...) or have a single line {B286C06B-0879-11D2-AACA-00C04FA33C20}, which signifies an unknown coordinate system.

tndcs.abf - Statistic of tag usage

Contains an array of 24 byte big data set, one for each used tag. The data set contains the tag and the number of points with that tag. Each data set is structured as follows:

Bytes Type Endianness Usage
0–3 int32 little Number of the entry; starting with 1
4–7 int32 little Tag value
8–11 int32 little Unused; always 0; maybe reserved for extending tag values to 64 bit
12–15 int32 little Number of points with the tag
16–19 int32 ? little Unused; always 0
20–23 int32 ? little Unknown; always 0 in ArcGIS 9, different values in ArcGIS 10

tnval.abf - Point tag file

Contains are array of 4 byte integer value, one for each (tagged) point of the TIN. The values are stored in little-endian byte order. Superpoints have the value 0 (zero). Points without a tag (e.g. points added by breaking edges) must be stored last in the TIN, and don't have an entry in this file.

Format changes and files new with ArcGIS 10

Since ArcGIS 10 there were some changes in the TIN file format. 2 new files (teval.dbf and tnodinfo.dbf) and 1 file got remained.

tdenv9.dbf - tdenv.dbf renamed

The file structure remains the same, just the field containing the number of breaking edges is additionally used.

tnodinfo.dbf - More informations for the points

Contains an array of 2 byte integer values. One short for each point. The purpose is still not publicly known. So far it seems to be some kind of bitmask or code, describing the usage of the point. The values seem to be stored in big-endian byte order.

Value Hexadecimal value Usage
2 0x0002 Superpoint
4 0x0004 Regular point
24 0x0018 ?
88 0x0058 ?
132 0x0084 ?
280 0x0118 ?
284 0x011C ?
376 0x0178 ?
516 0x0204 ?
772 0x0304 ?
796 0x031C ?

teval.dbf - The new breaking edge file (part 1)

Contains an array of data sets defining the breaking edges of the TIN, two for each breaking edge (one for each direction). Each data set is 16 byte long and structured as follows:

Bytes Type Endianness Usage
0–3 int32 big Index of point definition (index of a point) and edge definition (index of the edge) of the neighbouring triangle in tnod.adf or tedg.adf that form a breaking edge
4–7 int32 big Index of point definition (index of a point) and edge definition (index of the edge) of the current triangle in tnod.adf or tedg.adf that form a breaking edge
8–11 int32 big Type of the breaking edge (4 for hard edges, 2 for soft edges)
12–15 int32 big Unused; always 0

tedg.dbf - The new breaking edge file (part 2)

Since ArcGIS 10 this file has changed a little. It still contains a dataset for each triangle, and the references/indices of regular edges are unchanged, but the encoding of breaking edges is different. Breaking edges are still marked using negative values, but the index don't point to the file position in tnod.dbf and tedg.dbf anymore, instead the absolute of the value is the number of the entry of the breaking edge in teval.dbf. The encoding of soft edges has moved to teval.dbf, too.

Superpoint

In this article the term 'superpoint' is used at several locations. In the absence of an official file format description this term was chosen to reflect the properties of these points. (They could also have been called 'metapoint', 'extrapoint', 'infinity point' and many more.) An superpoint in the context of the Esri TIN file format is an additional point added by the ArcGIS software during triangulation/generation of the TIN. ArcGIS usually adds 4 of these points, one each west, north, east and south of the regular TIN points, at an extremely high distances. The superpoints are usually the first points in the point files tnxy.adf and tnz.adf. The triangles that are build with these points are usually masked (made invisible) in the tmsk.adf file.

See also

References

  1. 1 2 Samaga, Uta. "Kartographische 3D-Modellierung mit dem ArcView 3D-Analyst" (PDF). Retrieved 2015-04-27.
  2. 1 2 Ormsby, Tim; Alvi, Jonell. Extending ArcView GIS. ISBN 978-1-879-10205-7.
  3. ↑ "Lecture on Surfaces by Ronald Briggs, Ph.D., GISP". Retrieved 2015-04-27.
  4. ↑ "Virtual Terrain Project ITF ("Intermediate TIN Format") format description". Retrieved 2015-04-27.
  5. 1 2 3 4 "Source code of the Virtual Terrain Project reading Ersi TIN". Retrieved 2015-04-27.
  6. ↑ "GeoEco Python Reference on ConvertSpatialReference Method". Retrieved 2015-04-27.

External links

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