Orientation data are either unit vectors, referred to as vectorial or directed data; or unit axes, referred to as axial or undirected data. Current flow directions, for example, are directed, while fold axes are undirected. Plotting, contouring, and statistical analysis of these data types is different. Geometrically, data represents either lines or planes, which can be directed or undirected. On spherical projections planes and lines are considered to pass though the center of a unit sphere. Planes are represented by either their great circle, the intersection of the plane with the unit sphere, or by their normal (often referred to as the plane's pole).
Unit vectors or axes in three dimensions can be specified by their coordinates on the surface of the unit sphere, these are the direction cosines. However, it is more common to specify just two independent angles, a horizontal angle and a vertical angle. Two dimensional data only requires a horizontal angle. Orient has separate columns for lines and for planes, primarily so fault data, which requires both, can be entered easily. Enter all plane data in the plane columns, and line data in the line columns. Unused columns can be hidden if desired.
Orient's standard coordinate system is a right-handed system defined by [X, Y, Z] = [right, top, up]. Spherical coordinates are specified as longitude (theta), the counterclockwise angle from X in the XY plane, and colatitude (phi) the angle from Z. Alternatively, coordinates are specified by direction cosines in this coordinate system. Planes are represented by their upward normal. This is normally transparent to the user, as coordinates are converted to and from user coordinate systems for data entry and output. However, for rotations the user should be aware of the standard coordinate system.
Geographic data generally uses longitude as the horizontal angle. The vertical angle is commonly latitude or colatitude. Geologic data, however, typically uses azimuths for horizontal angles, which are measured clockwise from Y (North). User coordinates are typically strike and dip for planes, or trend and plunge for lines. However, all common conventions are supported, including dip direction, declination, inclination, zenith, and altitude (see Appendix). Orient can convert among these conventions.
There are several conventions for strike and dip. By default Orient uses the common convention that the dip is to the right looking along the strike (the right hand rule). A second convention, where the dip is to the left (the thumb of the right hand points down the dip), is referred to as Strike left. This convention can be selected using the Data Format command. A third convention, where a dip octant (N, NE, E, SE, etc.) is required is automatically converted as described in the next section
Angle units can be set as degrees, gradians (grads), or radians. The format applies to all angles and is set using the Data Format command. The default is degrees.
Each data point must include a pair of angles specifying it's orientation in space. The first angle is measured in a horizontal plane, and the second in a vertical plane. For typical geological data, these would be strike and dip for planes, or trend and plunge for lines. However, all common conventions are supported. Two dimensional data only require horizontal angles.
Before entering data, select the correct data format using the Data Format command. You may also wish to hide or show appropriate columns using the Data View Options command. Note that separate columns are used for planes and for lines, so make sure the required columns are visible. The Type column can contain any alphanumeric identifier, and is optional. Specifying a type is required, however, if multiple data types are entered in a single file. Also, settings, such as symbol sizes and color, are saved for each type.
Additional fields include station identifiers, X, Y and Z coordinates, domains, and comments, these are listed in the Appendix. X and Y coordinates are required for domain analysis as described later.
Orient does several automatic data conversions. An older format used for compass readings of horizontal angles is a bearing. These are given as degrees east or west of north or south, for example, N30W. When entering data in degrees in an azimuth format (such as strike or trend) bearings are automatically converted to azimuths, for example: N30W converts to 330.
A conversion is also done for plane data entered with a dip octant (N, NE, E, SE, S, SW, W, or NW). Enter the strike first, and then the dip with dip octant. The strike will then be corrected to a strike (or strike left, if that convention is being used). For example: [strike, dip] = [10, 30w] converts to [190, 30].
When entering fault data several conversions apply. First enter the fault plane orientation. Then, if the slip trend is entered, the plunge is automatically calculated. If the slip plunge is entered instead, the trend is automatically calculated. If the plunge is not a possible value (greater than the dip) it will be highlighted in red. To enter the slip as a rake (pitch), enter the rake value in the plunge field followed by the letter 'k', and the rake will be converted to a plunge. By convention, the rake is the clockwise angle about the upward normal of the plane measured from the strike (with right hand thumb as upward normal, rake is measured opposite from fingers).
Fault slip data is directed and must be entered as such. Normal faults have a positive plunge (inclination), and reverse faults a negative plunge. To assist in entering slip data use 'n' and 'r' to convert between the two. For example, [trend, plunge] = [10, 30] gives a normal slip, while [10, 30r] converts to [190, -30] which is a reverse slip. [190, -30n] converts back to [10, 30]. This convention can be combined with 'k' when entering a rake.
Data entry can be done using Orient's spreadsheet interface, or by importing a tab delimited file TSV (Tab Separated Value) or TXT file from Excel, another spreadsheet, or a text editor. The File Import Data command allows import of many additional text file formats. File format details are given in the Appendix.