The triangulated file format is used to represent deformation or velocity components of a deformation model. The format defines the values at a set of points, and how the points are connected to form a triangulation. The triangulation is assumed to be valid - that is no triangles are overlapping. The current limitations of the model also require that the outer boundary of the triangulation is convex. Note that where the triangulation is defined in terms of latitude and longitude the triangluation takes no account of curvature, either in forming the triangles or in interpolating values across them.
A triangulated data file can be constructed using the maketrig.pl perl script supplied with SNAP. This builds a binary format triangulation file based on a text format defined below. The SNAP programs only used triangulated data as part of a deformation model file, which is built directly from the text format.
The text format comprises a set of header records followed by records defining the values at each grid node, and then records defining each triangle. Each record comprises a code defining the contents of the record, followed by a colon and the value of the record.
The records are as follows:
| Code |
Type |
Description |
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| FORMAT |
string |
Defines the variant of the binary trig file format to generate. The possible values are
|
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| HEADER0 |
string |
Descriptive information about the model (an arbitrary character string) |
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| HEADER1 |
string |
Descriptive information about the model |
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| HEADER2 |
string |
Descriptive information about the model |
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| CRDSYS |
string |
Code for the coordinate system upon which the model is based (for example NZGD2000) |
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| NDIM |
integer |
The number of values defined at each node |
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| P |
string |
Defines a triangulation node. The string defines an integer node id, longitude, latitude, and the NDIM data values at the node. |
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| T |
string |
Defines the set of nodes on a triangle face in terms of their node ids. The nodes must be ordered in an anticlockwise direction around the triangle. |
An example of a text format triangulation file follows:
FORMAT TRIG1L HEADER0 Fiordland earthquake July 2009 HEADER1 Coseismic deformation HEADER2 Initial model - horizontal deformation only CRDSYS NZGD2000 NDIM 2 P 1 176.189748 -39.978909 -1.718 -2.976 P 2 176.200639 -39.999405 -2.471 -4.280 P 3 176.199652 -39.999242 -2.472 -4.282 P 4 176.233484 -40.035296 0.878 1.521 P 5 176.206731 -40.002636 2.259 3.913 P 6 176.185682 -40.034024 1.270 2.199 P 7 176.206435 -39.985896 -1.983 -3.435 P 8 176.203769 -40.002379 2.351 4.073 ... ... ... T 2 14 28 T 2 28 15 T 1 7 82 T 1 82 18 T 1 18 41 T 1 41 44 T 1 44 71 T 1 71 47 T 1 47 31 T 1 31 7 ... ... ...