Resolution and clipping

On the Resolution and Clipping form (prepare > Surfaces > Create Surface > Resolution and Clipping) you define the following settings for your output surface:

  • The resolution, which determines the 'coarseness' of the output surface.
  • The clipping boundary.

You can derive the resolution from an existing surface in your solution via the Autofill Parameters button on the form, or you can enter it from scratch. The resolution is indefinite; the edge of the output surface is defined by the clipping boundary. Various clipping options are provided but the options presented depend on the output representation and whether the surface is based on input data, or not (see overview table below).

To set the resolution and clipping boundary

  1. Open the Resolution and Clipping form.
  2. Select the surface definition of interest at the top of the form.

    3. Setting the resolution

  3. Enter the resolution with the Autofill Parameters button (continue with step 3a) or manually (continue with step 3b).
    4. When your output surface is a fault, the Easting and Northing entry fields are not shown on the form as they have no relevance.
    1. Click the Autofill Parameters button . The Autofill Parameters dialog opens.

      2. On the Autofill Parameters dialog, select the Source, Representation and Name of the object from which you want to derive the resolution settings. If the object is an event, only tri-mesh and 2D grid representations can be used. You can also derive the resolution from a seismic survey, fault model, structural model, 3D mesh structural model or 3D grid in your solution, an 'area' stored in the 'Area' folder (see Area Tool) or another existing 'surface definition' that you defined with the Create Surface workflow.

      When you have made your selections on the Autofill Parameters dialog, click OK and continue with step 4 to set the clipping boundary.

    2. Location and Orientation Enter the Easting, Northing and Azimuth (GN). The Easting and Northing are only used as reference point for the resolution you will enter in the next step, except when you select 'Specified rectangle' as clipping boundary in step 4, in which case the Easting and Northing form the south-west corner point (assuming you have an azimuth (GN) of 0) of the rectangle.

      3. Under Resolution, enter the X increment and Y increment, also called 'step length' in the X and Y direction. This will determine the distance between the nodes (for tri-meshes this is less exact) of the output surface.

    Setting the clipping boundary

  4. Under Method, select how you want to clip the edge of the output surface. The options available depend on the type of output surface and whether it is based on input data. The table below gives an overview:
    5. Output surface: Fault Output surface: Horizon, Unconformity or Intrusion
    Based on input data Based on input data Not based on input data
    Smallest rectangle around data Smallest rectangle around data x
    x Specified rectangle Specified rectangle
    Boundary polyline Boundary polyline Boundary polyline
    Convex hull Convex hull x
    Fit around data x x

    Special remarks on input data and clipping:

    • Clipping happens along the same projection normal as the interpolation, in other words, both clipping and interpolation use the same projection normal. For horizons, unconformities and intrusions the projection normal is vertical; for faults, the projection normal is the one as specified on the form (either auto-calculated or user-specified) and should ideally be the normal to the fault plane. It is therefore recommended for faults to choose a clipping boundary which lies (more or less) in the fault plane.
    • Every node and/or marker of the assigned representations that has not been set to 'inactive' on the Clean Up Data form is considered input data. One single node in a far corner of the field will influence the output surface when you choose a clipping boundary that derives its shape from the input data.
    • Clipping takes place after interpolation. This means that the interpolation algorithm incorporates all the input data (except input data set to 'inactive'), also any input data that fall outside of the selected clipping boundary. This can mean that much more data is interpolated than what is 'seen' on the final output surface when large areas with input data fall outside of the clipping boundary.

    Select one of the following clipping boundaries:

    Smallest rectangle around data  The boundary is the smallest enveloping rectangle around the input data. Not recommended for faults.

    Specified rectangle  This option clips the output surface at a user-specified rectangle. The origin (south-west corner point when Azimuth (GN) is 0) of this rectangle is formed by the Easting and Northing you entered in step 3. From the origin, the size of the rectangle is defined as follows:

    • X direction steps - Enter the number of X increments: the size of the rectangle in X direction is this number times the X increment.
    • Y direction steps - Enter the number of Y increment: the size of the rectangle in Y direction is this number times the Y increment.

    Boundary polyline The output surface is clipped according to a boundary polyline you select from the drop-down list. All boundaries in the Data > Boundary folder are listed. You need to have a boundary polyline available in your solution in order to use it as clipping boundary.

    You can create a boundary polyline with the editing tools. See Creating surface representations, markers and well designs for creating a new polyline set, and see Editing polylines for adding a polyline to the created polyline set. Once created, in the Property Inspector, set the Surface type to 'Boundary'. Note that only boundaries which consist of a single, closed polyline can be used, else you are prompted with an error upon creating the property.

    Convex hull  This option creates a convex hull around the data points. Recommended clipping option for faults.

    Fit around data  This option closely follows the input data. It allows concave shapes but no gaps. Only use this option when your input data is densely specified throughout the input data set.

  5. When you finished setting the resolution and clipping boundary, click Apply to save the settings and keep the form open or click OK to save the settings and move to the next workflow step Define Interpolation.