CONTACTX

Description

Contactx creates an output vector segment. The vector segment consists of line segments which trace the intersection of a plane with the surface of a digital elevation model (DEM). The plane is defined from the dip and strike angles of the input shape, which are set by the DIP program. Alternatively, they may be set as parameters in this program.

Parameters

Name	Type	Length	Value range
InputElev: Input elevation channel *	Raster port	1 - 1
InputVec: Input vector channel *	Vector port	1 - 1
Shape Number *	Integer	1 - 1
OutputVec: Output vector layer	Vector port	0 - 1
DBVD	String	0 - 1
Background Gray-Level Value	Float	0 - 1
Contact extension circle size	Float	0 - 1
Dip Angle	Float	0 - 1	0 - 90
Strike Direction (deg)	Float	0 - 1	0 - 360

* Required parameter

Parameter descriptions

InputElev: Input elevation channel

Specifies the input image channel containing the digital elevation (DEM) data. The input image channel can be of any type.

InputVec: Input vector channel

Specifies the input vector layer to process.

Shape Number

Specifies the input shape that contains one vertex with dip and strike angles.

OutputVec: Output vector layer

Specifies the layer to receive the transformed data.

DBVD

Optionally describes (in up to 64 characters) the contents or origins of the output data.

Background Gray-Level Value

Specifies the background gray-level, or no-data value, for the input DEM image.

Input pixels set to the background value are assumed to have an unknown elevation, and are not used for extension calculation. If BACKVAL is not specified, all input pixels are assumed to have valid elevation values and all are used for contour generation. BACKVAL is usually set to zero, where the raster image is not rectangular and zeros are used around the border of the image.

Contact extension circle size

Specifies the radius in date units (typically meters) of the circular area around the contact point.

The intersection of this circular area with the area defined by the input image window becomes the area used for the contact extension. If RADIUS is not specified, DBIW is used.

Dip Angle

Specifies the angle of dip in degrees, from 0 to 90. This value overwrites the dip attribute in the shape. If this parameter is specified, STRIKE must also be set.

Strike Direction (deg)

Specifies the strike direction in compass degrees, from 0 to 360. This value overwrites the strike attribute in the shape. If this parameter is specified, DIP must also be set.

Details

CONTACTX creates an output vector segment consisting of line segments that trace the intersection of a plane with the surface of a digital elevation model (DEM). The plane is defined from the dip and strike angles of the input shape, which are set either by the DIP function or by the DIP and STRIKE parameters in this function.

In geology, a contact refers to the portion of a rock layer which is visible at the surface. If the rock unit forms a layer, the orientation of the rock layer, if assumed to be planar, can be described by measuring the strike direction and the dip angle. These are explained in more detail in the DIP function. If the rock layer intersects the surface, the contact may appear as a line, which traces the intersection of the plane defined by the rock layer with the surface. The contact is not always visible at the surface (vegetation or other debris may disguise it). Contact extension takes a point on the ground, where the contact is known to be present, and creates a vector segment that traces the contact from that point out to the edges of a defined area (given the assumption that the layer is planar).

If the dip, strike, contact point, and assumptions of linearity are correct over the area that the contact extension uses, and if the DEM is properly georeferenced and accurate, the line segments calculated should follow the trace of the contact at the surface.

If this is not the case, it indicates that one of the conditions has not been met. This may mean that folding and/or faulting is present. Thus, the dip and strike values change along the contact and the assumption of linearity has failed. CONTACTX can therefore be used to check for folding and faulting. Other common problems include poor DEMs or improper georeferencing.