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	Caption	Length	Value range
FILI *	String	Input file name	1 - 192
FILO *	String	Output file name	1 - 192
DBIC *	Integer	Input elevation channel	1 - 1
DBIW	Integer	Input window	0 - 4	Xoffset, Yoffset, Xsize, Ysize
DBIV *	Integer	Input vector channel	1 - 1
SHAPE *	Integer	Input shape number	1 - 1
DBVN *	String	Output vector layer name	1 - 8
DBVD	String	Output vector layer description	0 - 64
BACKVAL	Float	Background gray-level value	0 - 1
RADIUS	Float	Contact extension radius	0 - 1
DIP	Float	Dip angle	0 - 1	0 - 90
STRIKE	Float	Strike direction	0 - 1	0 - 360
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILI

Specifies the name of the PCIDSK file containing the input vector layer to process.

FILO

Specifies the name of the PCIDSK file to receive the transformed data. FILO can be the same as FILI.

DBIC

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

DBIW

Specifies the raster window (Xoffset, Yoffset, Xsize, Ysize) that is read from the input layers. If DBIW is not specified, the entire layer is used by default. Xoffset, Yoffset define the upper-left starting pixel coordinates of the window. Xsize is the number of pixels that define the window width. Ysize is the number of lines that define the window height.

DBIV

Specifies the input vector layer to process.

SHAPE

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

DBVN

Specifies a name (up to 8 characters) for the output vector layer.

DBVD

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

BACKVAL

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.

RADIUS

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

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

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.

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

• ON: Turns the monitor ON (default)
• OFF: Turns the monitor OFF (recommended if running in batch or background mode)

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.

Example

Perform a contact extension on channel 1 and layer 1, shape 1 of image file irvine.pix, and save the vertices in the new vector layer with the name "TestExt" and description "Test of set contact extension" of the same file:

EASI>FILI    =   "irvine.pix"
EASI>FILO    =   "irvine.pix"
EASI>DBIC    =   1           ! input DEM layer
EASI>DBIW    =               ! process entire database
EASI>DBIV    =   25          ! input vector segment 25
EASI>SHAPE   =   1           ! input shape
EASI>DBVN    =   "TestExt"   ! output layer name
EASI>DBVD    =   "Test of set contact extension" ! ouptut layer description
EASI>BACKVAL =
EASI>RADIUS  =   1000        ! contact extension circle size
EASI>DIP     =   50          ! dip angle 50 degrees
EASI>STRIKE  =   100         ! strike direction 100 degrees
EASI>LASC    =               ! updated with output segment number
EASI>REPORT  =
EASI>MONITOR =

EASI>RUN CONTACTX