# 2. The VTK file format¶

There are primarily two types of VTK files, legacy and XML. We are going to focus on the legacy files, since they are a little bit simpler.

• VTK files can represent a single timestep.
• If you have multiple times you can group them with a .visit file.
• VTK files can be text or binary
• Both text and binary files have text meta data.
• Binary files have binary fields and coordinates imbedded in the text.
• VisIt has conventions for additional meta data that fits within the VTK specification.

The remainder of this VTK documentation consistes of a description of the file format, a simple example, and then more complex examples of the different mesh types.

The official VTK file format descriptions can be found at the VTK website.

Warning

Reading VTK files into VisIt requires strict file extension matching. For example, if you have a pvtu file, it must have the .pvtu extension or VisIt will not be able to open and read the file. This is true even when using VisIt’s feature to explicitly specify the plugin to use to open the file. For example, if you know file.foo is a VTK file and try to open it using VisIt’s VTK plugin, it will fail because the extension does not match a known extension for VTK files. For VisIt to read VTK files, the files must have the correct VTK extensions.

## 2.1. The visit_writer source and header files¶

The visit_writer.c and visit_writer.h files contain C source code with simple functions that write VTK files that can easily be added to your existing C or C++ data generating code without introducing any external dependencies. The library can write either text or binary files. The library can output point, unstructured, rectilinear, regular and curvilinear meshes.

The header and source files can be found in the VisIt repository on GitHub.

## 2.2. Binary files¶

Binary files contain binary coordinates and fields. This is any data where a length and data type are specified. The binary data follows immediately after the newline character of the previous ASCII keyword and parameter sequence. Binary data must be written in big endian format. If you are on a little endian system, you will need to byte swap the data before writing it. X86 and ARM processors store data in little endian format, so you will need to byte swap the data in that case. If you want to write your code independent of the endianness, you can write code to detect it and do the byte swapping if appropriate. The visit_writer mentioned above contains code to detect the endianness and do byte swapping if necessary.

## 2.3. The basic structure of a VTK file¶

A VTK file consists of 5 sections.

1. The first section is the file version and identifier. This section contains the single line: # vtk DataFile Version 3.0.

2. The second section is the title. The title must be on a single line and can be at most 256 characters.

3. The next section is the file format. The file format describes the type of the file, either ASCII or binary. The type must be on a single line and contain either the word ASCII or BINARY.

4. The fourth part is the mesh structure. It contains the points and the topology. This part begins with a line containing the keyword DATASET followed by a keyword describing the type of dataset. Then, depending upon the type of dataset, other keyword/data combinations define the actual data. The topology can be 1D, 2D or 3D, although only 2D and 3D topologies are supported by VisIt. If the Z-coordinates are all zero, VisIt will treat the mesh as 2D and display it in 2D.

5. The final part describes the fields. The fields can be defined on either the cells or the points. The cell or point fields can be listed in either order. The fields can be either scalars, vectors or tensors.

### 2.3.1. Mesh topology¶

The following mesh topologies are supported.

• Structured points
• Structured grid
• Rectilinear grid
• Polydata
• Unstructured grid

#### 2.3.1.1. Structured points¶

The structured points section has the following structure.

DATASET STRUCTURED_POINTS
DIMENSIONS nx ny nz
ORIGIN x y z
SPACING sx sy sz


nx, ny, nz are the number of dimensions in the X- Y- and Z-directions. x, y, z is the origin of the grid. sx, sy, sz is the spacing in the X- Y- and Z-directions.

#### 2.3.1.2. Structured grid¶

The structured grid section has the following structure.

DATASET STRUCTURED_GRID
DIMENSIONS nx ny nz
POINTS nPoints dataType


nx, ny, nz are the number of dimensions in the X- Y- and Z-directions. nPoints is the number of points. nPoints must be consistent with the dimensions. Supported data types in VisIt are float and double.

#### 2.3.1.3. Rectilinear grid¶

The rectilinear grid section has the following structure.

DATASET RECTILINEAR_GRID
DIMENSIONS nx ny nz
X_COORDINATES nx dataType
x1 x2 ... xn
Y_COORDINATES ny dataType
y1 y2 ... yn
Z_COORDINATES nz dataType
z1 z2 ... zn


nx, ny, nz are the number of dimensions in the X- Y- and Z-directions. nx, ny, nz in the dimensions statement must be constient with the ones in the coordinates statement. Supported data types in VisIt are float and double.

#### 2.3.1.4. Polydata¶

The polydata grid section has the following structure.

DATASET POLYDATA
POINTS nPoints dataType
x1 y1 z1
x2 y2 z2
...
xn yn zn

VERTICES nVertices size
1 p1
1 p2
...
1 pn

LINES nLines size
2 l11 l12
2 l21 l22
...
2 ln1 ln2

POLYGONS nPolygons size
n1 i11 i12 ... i1n1
n2 i21 i22 ... i2n2
...
nn in1 in2 ... innn

TRIANGLE_STRIPS nStrips size
n1 i11 i12 ... i1n1
n2 i21 i22 ... i2n2
...
nn in1 in2 ... innn


Supported data types in VisIt are float and double. The vertices, lines, polygons and triangle_strips sections may or may not be present. The vertices, lines, polygons and triangle_strips sections may be in any order. xn, yn and zn are the coordinates of the nth point. n1, n2 and nm are the number of indices for each cell. in1, in2 and innn are the zero origin indices for the nth cell.

#### 2.3.1.5. Unstructured grid¶

The unstructured grid section has the following structure.

DATASET UNSTRUCTURED_GRID
POINTS nPoints dataType
x1 y1 z1
x2 y2 z2
...
xn yn zn

CELLS nCells size
n1 i11 i12 ... i1n1
n2 i21 i22 ... i2n2
...
nn in1 in2 ... innn

CELL_TYPES nCells
t1
t2
...
tn


Supported data types in VisIt are float and double. The cells and cell_types sections may be in any order. xn, yn and zn are the coordinates of the nth point. n1, n2 and nm are the number of indices for each cell. in1, in2 and innn are the zero origin indices for the nth cell. t1, t2 and tn are the cell types for each cell.

The following cell types are supported.

Type Value Type Value
VTK_PIXEL 8 VTK_CUBIC_LINE 35
VTK_VOXEL 11 VTK_LAGRANGE_TETRAHEDRON 71
VTK_HEXAHEDRON 12 VTK_LAGRANGE_HEXAHEDRON 72
VTK_WEDGE 13
VTK_PYRAMID 14

### 2.3.2. Cell data¶

The cell data section starts with a single line with the keyword CELL_DATA followed by the number of cells. The number of cells must match the number of cells defined by the topology. Next comes a list of fields. Fields can be either scalars, vectors or tensors.

#### 2.3.2.1. Scalar fields¶

The scalar field section has the following structure.

SCALARS fieldName dataType 1
LOOKUP_TABLE default
s1 s2 ... sN


The scalar field section starts with a single line with the keyword SCALARS followed by the name of the field followed by the data type followed by the number of values per scalar. The number of values per scalar is optional, and if present, must be 1. Next comes the lookup table information. The lookup table information consists of a single line with the keyword LOOKUP_TABLE followed by the keyword default. The lookup table specifies the lookup table name when mapping the scalar to colors. The lookup table is not used by VisIt. Next come the scalar values. The scalar values can be split up into lines in an arbitrary manner.

#### 2.3.2.2. Vector fields¶

The vector field section has the following structure.

VECTORS fieldName dataType
v11 v12 v13
v21 v22 v23
...
vn1 vn2 vn3


The vector field section starts with a single line with the keyword VECTORS followed by the name of the field followed by the data type. Next come the vector values. The vector values consist of three values per point, regardless of whether it is for a 2D or 3D mesh. The vector values can be split up into lines in an arbitrary manner.

#### 2.3.2.3. Tensor fields¶

The tensor field section has the following structure.

TENSORS fieldName dataType
t111 t112 t113
t121 t122 t123
t131 t132 t133
t211 t212 t213
t221 t222 t223
t231 t232 t233
...
tn11 tn12 tn13
tn21 tn22 tn23
tn31 tn32 tn33


The tensor field section starts with a single line with the keyword TENSORS followed by the name of the field followed by the data type. Next come the tensor values. The tensor values consist of nine values per point, regardless of whether it is for a 2D or 3D mesh. The tensor values can be split up into lines in an arbitrary manner.

### 2.3.3. Point data¶

The point data section starts with a single line with the keyword POINT_DATA followed by the number of points. The number of points must match the number of points defined by the topology. The rest of the point data section is the same as the cell data section.

### 2.3.4. Field data¶

Field data is an array of data arrays that can be associated with a DATASET, CELL_DATA or POINT_DATA.

Field data has the following general format.

FIELD FieldData numberOfFields
FieldName numberOfComponent numberOfTuples dataType
t11 t12 ... t1cn
t21 t22 ... t2cn
...
tn1 tn2 ... tncn


The field data section begines with a single line that starts with the keywords FIELD and FieldData followed by the number of fields. Next come the fields. Each field starts with a single line with the field name, the number of components, the number of tuples and the data type.

## 2.4. VisIt meta data conventions for VTK files¶

VisIt supports a number of conventions for storing additional data. This data is stored as FIELD data as additional information in the DATASET, CELL_DATA or POINT_DATA.

The Following meta data is stored as DATASET FIELD data.

### 2.4.1. MeshCoordType¶

This specifies if the mesh coordinates are 2D cylindrical coordinates. If the value is a 1, it is an R-Z mesh. If the value is a 2, it is a Z-R mesh.

Here is an example of specifying the mesh coordinate type.

MeshCoordType 1 1 int
2


### 2.4.2. MeshName¶

The mesh name is represented as a string.

Here is an example of specifying the mesh name.

MeshName 1 1 string
rectmesh2d


### 2.4.3. CYCLE¶

The cycle is specified as a single integer value.

Here is an example of specifying the cycle.

CYCLE 1 1 int
10


### 2.4.4. TIME¶

The time is specified as a single double precision value.

Here is an example of specifying the time.

TIME 1 1 double
10.0


### 2.4.5. VisItExpressions¶

Each string represents a single expression. The string contains the expression name, the expression type and the expression. The three properties are seperated by semicolons. The expression type consists of one of curve, scalar, vector, tensor, array, material or species.

Here is an example of specifying the expressions.

VisItExpressions 1 2 string
vel;vector;{u,v}
speed;scalar;sqrt(u*u+v*v)


### 2.4.6. avtGhostZones¶

The ghost zones specify a flag indicating if the zone is a ghost zone or a real zone. A one indicates a ghost zone. A zero indicates a real zone. The ghost zone meta data is stored as CELL_DATA FIELD data.

Here is an example of specifying ghost zones.

FIELD FieldData 1
avtGhostZones 1 12 unsigned_char
1 0 0 1
1 0 0 1
1 0 0 1


## 2.5. An example VTK file¶

A basic VTK file is shown here.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET RECTILINEAR_GRID
DIMENSIONS 3 2 2
X_COORDINATES 3 float
0 1 2
Y_COORDINATES 2 float
0 1
Z_COORDINATES 2 float
0 1

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 12
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3 1 2 3 1 2 3


The line below contains the version and identifier.

# vtk DataFile Version 3.0


The line below contains the title.

vtk output


The line below contains the data type, which in this case is ASCII.

ASCII


The line below identifies the type of the mesh, which in this case is a rectilinear grid.

DATASET RECTILINEAR_GRID


The following lines provide the coordinate information for the mesh.

DIMENSIONS 3 2 2
X_COORDINATES 3 float
0 1 2
Y_COORDINATES 2 float
0 1
Z_COORDINATES 2 float
0 1


The information provides the dimensions of the coordinate arrays of the mesh along with the coordinates in each of the three directions.

The following lines represent one scalar field defined on the cells.

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2


The information tells us that there are 2 values for the cell data, that it is a scalar, that the name of the variable is density, that it should be read in as float values, that we should use the default lookup table, and that the values consist of 1 2.

The following lines represent one scalar field defined at the points.

POINT_DATA 12
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3 1 2 3 1 2 3


The information tells us that there are 12 values for the point data, that it is a scalar, that the name of the variable is u, that it should be read in as float values, that we should use the default lookup table, and that the values consist of 1 2 3 1 2 3 1 2 3 1 2 3.

## 2.6. An example of a VTK file with extra metadata¶

A VTK file with extra meta data is shown here.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET RECTILINEAR_GRID
FIELD FieldData 5
MeshCoordType 1 1 int
2
MeshName 1 1 string
rectmesh2d
CYCLE 1 1 int
10
TIME 1 1 double
10.0
VisItExpressions 1 2 string
vel;vector;{u,v}
speed;scalar;sqrt(u*u+v*v)

DIMENSIONS 5 4 1
X_COORDINATES 5 float
0 1 2 3 4
Y_COORDINATES 4 float
0 1 2 3
Z_COORDINATES 1 float
0

CELL_DATA 12
SCALARS density float 1
LOOKUP_TABLE default
1 2 3 4
5 6 7 8
9 10 11 12

FIELD FieldData 1
avtGhostZones 1 12 unsigned_char
1 0 0 1
1 0 0 1
1 0 0 1

POINT_DATA 20
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 4 5 1 2 3 4 5
1 2 3 4 5 1 2 3 4 5
SCALARS v float 1
LOOKUP_TABLE default


The following lines represent the mesh name associated with this file.

MeshName 1 1 string
rectmesh2d


The following lines represent cycle associated with this file.

CYCLE 1 1 int
10


The following lines represent the time associated with this file.

TIME 1 1 double
10.0


The following lines represent the expressions associated with this file.

VisItExpressions 1 2 string
vel;vector;{u,v}
speed;scalar;sqrt(u*u+v*v)


The following lines represent the ghost zones associated with this file.

FIELD FieldData 1
avtGhostZones 1 12 unsigned_char
1 0 0 1
1 0 0 1
1 0 0 1


## 2.7. An example of a structured points file¶

A structured points file results in a regular mesh with constant spacing in each direction. The mesh can be 2D or 3D. It is defined by specifying STRUCTURED_POINTS as the DATASET type in the mesh structure portion of the file.

Here is an example of a VTK file with 3D structured points.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 3 2 2
ORIGIN 0 0 0
SPACING 1 1 1

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 12
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3 1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2 1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


This defines a regular mesh consiting of 12 points and 2 cells. For the cells, it defines a single scalar variable named density. For the points, it defines 2 scalar variables named u and v, a vector variable named velocity, and a tensor variable named stress.

Here is an example of a VTK file with 2D structured points.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 3 2 1
ORIGIN 0 0 0
SPACING 1 1 1

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 6
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


This defines a mesh similar to the previous one except that it has one row of points in the Z-direction. Note that the number of dimensions in the Z-direction is 1 and that Z origin is zero. The spacing in the Z-direction is one, but it could be any value.

## 2.8. An example of a structured grid file¶

A structured grid file results in a structured mesh where the position of each node in the mesh is specified. The mesh can be 2D or 3D. It is defined by specifying STRUCTURED_GRID as the DATASET type in the mesh structure portion of the file.

Here is an example of a VTK file with a 3D structured grid.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_GRID
DIMENSIONS 3 2 2
POINTS 12 float
0 0 0
1 1 0
2 1 0
0 1 0
1 2 0
2 2 0
0 0 1
1 1 1
2 1 1
0 1 1
1 2 1
2 2 1

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 12
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3 1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2 1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


It defines a structured mesh that is the same as the structured point example except that the mesh points are no longer regular. This defines a structured mesh consiting of 12 points and 2 cells. For the cells, it defines a single scalar variable named density. For the points, it defines 2 scalar variables named u and v, a vector variable named velocity, and a tensor variable named stress.

Here is an example of a VTK file with a 2D structured grid.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_GRID
DIMENSIONS 3 2 1
POINTS 6 float
0 0 0
1 1 0
2 1 0
0 1 0
1 2 0
2 2 0

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 6
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


This defines a mesh similar to the previous one except that it has one row of points in the Z-direction. Note that the number of dimensions in the Z-direction is 1 and that the Z values are all zero.

## 2.9. An example of a rectilinear grid file¶

A rectilinear grid file results in a structured mesh where the coordinates along each axis are specified as a 1-D array of values. The mesh can be 2D or 3D. It is defined by specifying RECTILINEAR_GRID as the DATASET type in the mesh structure portion of the file.

Here is an example of a VTK file with a 3D rectilinear grid.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET RECTILINEAR_GRID
DIMENSIONS 3 2 2
X_COORDINATES 3 float
0 1 2
Y_COORDINATES 2 float
0 1
Z_COORDINATES 2 float
0 1

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 12
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3 1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2 1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


It defines a rectilinear mesh that is the same as the structured point example.

Here is an example of a VTK file with a 2D rectilinear grid.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET RECTILINEAR_GRID
DIMENSIONS 3 2 1
X_COORDINATES 3 float
0 1 2
Y_COORDINATES 2 float
0 1
Z_COORDINATES 1 float
0

CELL_DATA 2
SCALARS density float 1
LOOKUP_TABLE default
1 2

POINT_DATA 6
SCALARS u float 1
LOOKUP_TABLE default
1 2 3 1 2 3
SCALARS v float 1
LOOKUP_TABLE default
1 1 1 2 2 2
VECTORS velocity float
0 1 0
0 1 0
0 1 0
0 2 0
0 2 0
0 2 0
TENSORS stress float
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
1 0 0
0 1 0
0 0 1
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2
2 0 0
0 2 0
0 0 2


This defines a mesh similar to the previous one except that it has one row of points in the Z-direction. Note that in the Z-direction there is 1 value and that it is zero.

## 2.10. An example of a polydata file¶

A polydata file results in a points, lines and surface cells. The mesh can be 2D or 3D. It is defined by specifying POLYDATA as the DATASET type in the mesh structure portion of the file.

Here is an example of a VTK file with polydata.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET POLYDATA
POINTS 17 float
-5 -5  5
0 -5  5
5 -5  5
0  0 -5
0  0  5
0 -5  0
0  5  0
-5  0  0
5  0  0
-5 -5 -5
-5  5 -5
5  5 -5
5 -5 -5
-5 -5 -5
5 -5 -5
-5 -5  5
5 -5  5

VERTICES 3 6
1 0
1 1
1 2

LINES 3 9
2 3 4
2 5 6
2 7 8

POLYGONS 1 5
4 9 10 11 12

TRIANGLE_STRIPS 1 5
4 13 14 15 16

CELL_DATA 8
SCALARS density float 1
LOOKUP_TABLE default
1 2 3 4 5 6 7 8

POINT_DATA 17
SCALARS u float 1
LOOKUP_TABLE default
0 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2 2 3 3 3 3
SCALARS v float 1
LOOKUP_TABLE default
0 0 0 0.05 1 0.05 1 0.05 1 0.5 0.5 1 1 0.5 1 0.5 1


It supportes points, lines, polygons and triangle strips.

## 2.11. An example of a unstructured grid file¶

An unstructured grid file results in an arbitrary combination of cell types. The points are explicitly specified. The mesh can be 2D or 3D. It is defined by specifying UNSTRUCTURED_GRID as the DATASET type in the mesh structure portion of the file.

Here is an example of a VTK file with a 3D unstructured grid.

# vtk DataFile Version 3.0
vtk output
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 48 float
0 0 0
1 0 0
2 0 0
3 0 0
4 0 0
0 1 0
1 1 0
2 1 0
3 1 0
4 1 0
0 2 0
1 2 0
2 2 0
3 2 0
4 2 0
0 3 0
1 3 0
0 4 0
0 5 0
1 4 0
0 4 1
1 4 0
2 4 0
1 4 1
2 4 1
1 5 0
2 5 0
1 5 1
2 5 1
2 4 0
3 4 0
3 4 1
2 4 1
2 5 0
3 5 0
3 5 1
2 5 1
3 4 0
3 4 1
3 5 0
4 4 0
4 4 1
4 5 0
4 4 0
5 4 0
5 4 1
4 4 1
4 5 0

CELLS 17 82
1 0
1 1
3 2 3 4
2 5 6
2 6 7
3 7 8 9
3 5 10 6
3 10 6 11
4 6 11 7 12
4 7 12 13 8
4 8 9 13 14
4 10 15 16 11
4 17 18 19 20
8 21 22 23 24 25 26 27 28
8 29 30 31 32 33 34 35 36
6 37 38 39 40 41 42
5 43 44 45 46 47

CELL_TYPES 17
1
1
2
3
3
4
5
5
6
7
8
9
10
11
12
13
14

CELL_DATA 17
SCALARS density float 1
LOOKUP_TABLE default
1 1 2 3 3 4 5 5 6 7 8 9 10 11 12 13 14


It contains all the linear element types.