Structure Orientations

Structures logged in Insight are by default described by (drill core) internal orientation angles.

Global orientation angles can further be produced and exported when a hole orientation (collar data, see below) is set by the user.

Caution

All presented structure orientations are subject to a large number of possible error sources in the underlying drilling, transport and scanning processes. Particular error sources associated with the GeoCore X10 scanning process are therefore emphasized below.

Caution

Error source: All orientation angles except for α and γ are ill-defined if the sample was not oriented during scanning. Always proceed with caution when interpreting structural orientations.

You can verify that your sample was oriented during scanning by picking Show → Orientation Marks from the menu bar:

A red line representing the orientation mark will be shown in the Preview and 3D Tomography view for segments of core that have orientation information:

Internal Orientations

The drill core internal orientation of linear and planar structures are each described by two angles: α and β (planar structures) or γ and δ (linear structures).

Planar Structures

Planar structure angles are defined with respect to the major of axis of the intersection ellipse that forms between the plane of the structure and the drill core surface.

• The α angle (0-90°) is the acute angle between the core axis and the major axis.

• The β angle (0-360°) is the angle from the orientation line to the down-hole end of the major axis (the "apical trace"), measured positively around the down-hole core axis (i.e. clockwise in a plane orthogonal to the core axis, while looking in the drilling direction).

Linear Structures

Linear structure angles are defined with respect to the linear direction, translated to pass through the drill core axis.

• The γ angle (0-90°) is the acute angle between the core axis and the linear direction.

• The δ angle (0-360°) is the angle from the orientation line to the down-hole end of the linear direction (the "apical trace"), measured positively around the down-hole core axis (i.e. clockwise in a plane orthogonal to the core axis, while looking in the drilling direction).

Caution

Error source: The sample axis of the scan is currently used as an estimate for the true drill core axis. Particular care should therefore be exercised for samples of low structural integrity and when loading samples into the sample tube.

Global Orientations

To convert the internal orientation angles into a global orientation, the user must supply an orientation of the hole in form of hole collar data (optionally extended with down-hole survey data).

Collar Data

Collar data is set as a hole property using either Hole → Properties... in the menu bar or the Edit Hole Properties button in the structure manager:

First enable collar data:

Then enter the hole orientation:

The user must here supply the following four values:

• The Azimuth (0-360°) denotes the direction of the horizontal projection of the hole trajectory, measured as a clockwise angle from the north (as seen from "above" on e.g. a map).

• The Inclination (0-90°) denotes the acute angle between the hole trajectory and the horizontal plane. The angle will per default be assumed to measure below the horizontal plane.

• Top-of-hole marker (true or false) denotes that the orientation line of the hole has been marked along the top (i.e. the "roof"). It is otherwise oppositely assumed that the orientation line has been marked along the bottom (i.e. the "floor").

• Upwards inclination (true or false) denotes that the inclination (in contrast to the default assumption) measures above the horizontal plane. When shown to the user or exported, this will be represented as a negative inclination value.

Caution

Error source: Both the azimuth and top-of-hole marker values are ill-defined for the case of vertical holes (i.e. inclination ≈ ± 90°). As convention, the azimuth will then instead be assumed to denote the direction in which a top-of-hole orientation line would be marked for a downwards inclined hole.

Tip

The global orientations will be given in the same coordinate system as for which the user supplied the collar data. "North" could for instance indicate geographical north, magnetic north, or any other direction preferred by the user.

The global orientation of each structure is now shown as two angles: Dip and Direction (planar structures), Plunge and Trend (linear structures):

Down-hole survey

For an improved description of the hole orientation, the Azimuth and Inclination values may instead be provided as depth-dependent quantities by importation of down-hole survey data.

Insight allows import of down-hole survey data in CSV (Comma Separated Values) format. Enable down-hole survey data and click Load, then use the dialog to locate your CSV file:

Once the file has been loaded, select the appropriate columns to use as data:

The currently imported down-hole survey file is shown in the Hole Properties dialog:

An enabled down-hole survey overrides the manually entered Azimuth and Inclination values, whereas Top-of-hole marker and Upwards inclination still applies as before.

To determine Azimuth and Inclination for arbitrary depths, Insight uses a linear interpolation between the data points of the survey; for points that are outside of the surveyed depth range, the hole is assumed to continue in a straight segment from the closest point.

Caution

It is the user's responsibility to ensure a consistent and appropriate sign convention of Inclination values between the down-hole survey data file and it's usage in Insight, through careful inspection of the data and adjustment of the Upwards inclination value.

Planar Structures

With the upwards inclined normal of the structure as reference direction for planar structures, the global orientation angles are defined as:

• Dip (0-90°): the acute angle between the reference direction and the upwards axis (equal to the greatest slope of the plane).

• Direction (0-360°): the horizontal projection of the reference direction, measured as a clockwise angle from the north (as seen from "above" on e.g. a map).

Linear Structures

Similarly, with the downwards inclined direction of the structure as reference for linear structures, the global orientation angles are defined as:

• Plunge (0-90°): the acute angle between the reference direction and the horizontal plane.

• Trend (0-360°): the horizontal projection of the reference direction, measured as a clockwise angle from the north (as seen from "above" on e.g. a map).