X3p

x3p is a file format for 2D and 3D profile data. The file extension x3p can be memorized as XML 3-D Surface Profile. It is a container format conforming to the ISO5436-2 standard. It has been implemented to provide a simple and standard conforming way to exchange profile data. Due to its flexibility it can be used for point clouds without any topology as well as for projectable 2½D profile data and for multilayer profiles.

• Internal Structure
• Format of Binary Files
  • Matrix Structure
    • Matrix indexing
  • Data Order
• See Also

Internal Structure

The container’s directory structure consists of a central document named “main.xml”. The main document is an XML-file as defined in [Iso5436_2.xsd]. For a simple document the container comprises only “main.xml” and the checksum file “md5checksum.hex”. More complex documents, with larger amounts of data, can store the actual measurement data in a binary file. A link in “main.xml” points to the binary file. Binary files are stored in a subdirectory named “bindata”. The name of the binary file can be chosen freely. A recommended name is “data.bin”. The relative URI pointing to the binary file would in the default case look like “bindata/data.bin”.

To mark valid and invalid points in a binary file an optional matrix with the recommended name “bindata/valid.bin” can be stored. This file contains a packed array of Boolean values (a bit field). The value True (bit value 1) is associated with a valid point.

If the validity file does not exist all points are valid that do not have the special floating point value NaN (Not a Number).

Format of Binary Files

The binary file is a plain matrix of data points, written in binary format. The matrix has three dimensions. Each data point contains one ore more coordinates in X,Y,Z sequence and types specified in <DataType> in Record1 in “main.xml”.

Matrix Structure

The matrix always has three dimensions. By definition the matrix has to resemble the topological neighbourhood of the data points in the 3D-space. Clearly said two points that are neighbours in 3D have to be placed in neighbouring cells of the matrix grid.

Matrix indexing

The three dimensions of the matrix correspond to the three coordinate axes of the measured profile data. The first dimension corresponds to the x-axis, the second to the y-axis, and the third to the z-axis. The x-index is the fastest index y the next slower and z the slowest index. For a matrix of x-y-z-dimensions <Matrix>3;3;2</Matrix> the cell order of the points P(x,y,z) looks like the following example:

P(1,1,1), P(2,1,1), P(3,1,1),
P(1,2,1), P(2,2,1), P(3,2,1),
P(1,3,1), P(2,3,1), P(3,3,1),
P(1,1,2), P(2,1,2), P(3,1,2),
P(1,2,2), P(2,2,2), P(3,2,2),
P(1,3,2), P(2,3,2), P(3,3,2)

The indexing is used for binary files as well as for xml-data in the <DataList> tag. Data Types Possible data types are:

“I”: 16 bit signed integer in Intel byte order that is low byte (LSB) first.
“L”: 32 bit signed integer in Intel byte order that is LSB, 2nd SB, 3rd SB, MSB.
“F”: 32 bit IEEE 754 floating point number
“D”: 64 bit IEEE 754 floating point number

Data Order

Each cell can contain an X, Y and Z coordinate in this order. The X and Y coordinate are optional for points stored in a <DataMatrix>, depending on the types of axis defined. For an incremental X or Y axis, no X and Y-coordinates are written to the DataMatrix because the X- and Y- indices are defined by the matrix indices of a point.

See Also

• [Iso5436_2.xsd] Data type description of the xml document.
• ISO_5436-2 on German Wikipedia.