Generate fault from points
Fault modelling allows the creation of discontinuous surfaces where the discontinuity is provided by a dtm surface or a string segment representing an oblique fault or a vertical fault respectively. With the exception of the multiple surfaces function, all input and output of the fault creation and application functions are to and from graphics layers.
Faults may be created using points on the surface of the fault or by extending fault traces. The result of these routines is a dtm surface that represents the fault which may be subsequently used in the fault application functions. This function will create a fault from a set of points on its surface.
To run this function: Choose Surfaces > Fault modelling > Generate fault from points, or...
Select a point in the fault string
Select a point and all points belonging to the same string will be used to form a dtm surface. Note that all points are treated as spot heights, that is no breaklines are applied. The CREATE FAULT FROM POINTS form is then presented.
Output layer
Enter or select the graphics layer to which the fault dtm is to be drawn. If the nominated layer does not exist then it will be created.
Results
If a dtm could be formed, it is drawn to the nominated graphics layer.
Errors
A dtm already exists in the layer - appending as a solid
The layer into which the result is to be drawn already contains a dtm so the result is drawn as a 3DM. If you wish to generate a true dtm then re-run the function nominating a different layer.
Error creating fault surface
The geometry of the points prevented a valid dtm from being generated. This may occur if all points are co-linear or there are insufficient (less than 3) points to form the dtm.
Generate fault from trace
This function will create a fault from a trace or set of traces by extrapolation up and/or down the dip of the fault as specified globally or locally if the dip and dip direction of the fault are stored in description fields. If there are geometric ambiguities or paradoxes involved when local dips are projected it may not be possible to automatically form a valid dtm surface. With regard to such cases, a number of useful strings are also generated which may be used, in conjunction with Surpac's other design and surface modelling tools, to create the fault surface manually.
To run this function: Choose Surfaces > Fault modelling > Generate fault from trace, or...
Select the fault trace
Select a point and the CREATE FAULT FROM TRACE form is presented.
Traces in
Faults may be generated by the projection of a single segment which contains the selected point, or by the projection of all segments in the string that contains the selected point.
Upper elevation limit
Enter the elevation to which the up-dip projection of each point should be made. If this is left blank then there will be no up-dip projection.
Lower elevation limit
Enter the elevation to which the down-dip projection of each point should be made. If this is left blank then there will be no down-dip projection.
Dip
Either specify the dip which is to be applied at each point, or nominate a description field in which the dip may be found. A negative dip indicates downward projection. If a description field is nominated then points that do not have a valid dip (between -90.0 and 90.0) in that description field are ignored.
Dip Direction
Either specify the dip direction which is to be applied at each point, or nominate a description field in which the dip direction may be found. If a description field is nominated then points that do not have a valid dip direction (between 0.0 and 360.0) in that description field are ignored.
String Ids
Surface
Nominate a string number to which segments representing dip vectors at each point may be drawn. These are used as breaklines in the formation of the resultant surface.
Trace
Nominate a string number to which segments representing the up and down dip projections of each trace may be drawn.
Boundary
Nominate a string number to which the boundary of the resulting fault may be drawn. This may be useful in clipping the resultant fault dtm to delete extraneous triangles formed across the ends of non-planar faults.
Output layer
Enter or select the graphics layer to which the fault dtm is to be drawn. If the nominated layer does not exist then it will be created.
Results
If a dtm could be formed, it is drawn to the nominated graphics layer.
Errors
At least one limit (upper or lower) must be given
You must specify at least one of the elevation limits.
The upper limit given (999.99) is less than the minimum
Ensure that the number specified for the upper elevation limit is greater than that specified for the lower elevation limit.
The lower limit given (999.99) is more than the maximum
Ensure that the number specified for the lower elevation limit is less than that specified for the upper elevation limit.
The dip and direction must be specified by a description field (Dnn) or with a numeric value
Ensure that the dip and dip direction fields have been filled with either a number or a description field specification.
Value given in Dnn (999.99) is out of range 999.99 to 999.99
Warning that the dip or dip direction found in the description field Dnn of a point is beyond the allowable range.
No valid dip or dip direction was found in Dnn
Warning that the description field Dnn did not contain a valid numeric which could be used as a dip or dip direction.
Cannot expand point below lower limit
Warning given when a point that lies below the lower elevation limit is found. No down-dip projection is done for the point.
Cannot expand point above upper limit
Warning given when a point that lies above the upper elevation limit is found. No up-dip projection is done for the point.
Error creating fault surface
The geometry of the dip vectors prevented a valid dtm from being generated. This may occur if local dip and dip directions have been used and the vectors cross in their 2D projections.
A dtm already exists in the layer - appending as a solid
The layer into which the result is to be drawn already contains a dtm so the result is drawn as a 3DM. If you wish to generate a true dtm then re-run the function nominating a different layer.