Intersect Surfaces

Previous pageReturn to chapter overviewReturn to Top Next page












The actions in the Surface Intersection menu can be used to manipulate or generate surface geometry based on intersections with other surfaces (i.e., meshes or grids). The output will be in the form of new surfaces - the originals are not modified. Any number of surfaces (at least two) can be intersected at once. These tools are helpful for creating new geometry for use in modeling, but they are also important to ensure that model volumes are well-formed (i.e., clearly bounded and with no negative volumes).


These intersection tools do not constrain the "quality" of the output triangles. Although finite element analysis requires well-shaped triangles, all surface geometry used in SVOffice will be automatically re-meshed regardless, and therefore triangle aspect ratios should not be of concern in SVDesigner.




It is not always possible to guarantee a solution for a given intersection problem, depending on the current mesh settings and the complexity of the input surfaces. We recommend saving your conceptual model before continuing.
Be patient when intersecting large meshes, as the calculations may be very complex.


Various different intersection actions are available:


Fix Intersecting Geometry


This action does not modify surface shape, but rather it splits triangles where needed such that no triangles in any of the selected surfaces intersect each other (they will instead have shared segments where they used to intersect). This lack of triangle intersection is a requirement for volume meshing in SVOffice. Note that every other intersection tool used below implicitly performs this action as part of its operation, so it is not normally needed to use this explicitly. The exception is that this tool should be used when the output of one of the other intersection tools results in a warning that further intersections are needed.


Create Regions from Intersection Profiles


This action does not modify the surfaces in any way - instead, it outputs regions that define the lines of intersection between the surfaces (if any). If an intersection profile does not define a closed shape, it will be output as a polyline instead.


This action can be performed as part of any of the other actions described below, as an option available in the surface intersection dialog.


Build Up or Down


This action modifies any number of selected subject surfaces based on a single clip surface. Each surface may have its geometry moved up or down, depending on the chosen dialog option. For example, this action may be used to build a dam or pit into a terrain.


Carve Overlaps


This action modifies any number of selected subject surfaces based on a single clip surface. Each surface may have part of its geometry deleted, based on the chosen dialog option and whether the geometry is above or below the clip surface. For example, for a dam surface that extends both above and below a terrain, this action can be used to exactly remove the dam geometry that extends below the terrain.


Merge into New Surface


This action will output a single new surface that is the result of combining any number of selected surfaces together. Where multiple input surfaces are defined in a region, only the highest or lowest geometry will be kept (as chosen in the dialog).


Resolve Overlaps


This action modifies each surface based on the surfaces that are above it in the subject surfaces list. It modifies each surface's geometry such that it is not higher or lower (as chosen in the dialog) than the surfaces that are above it in the subject surfaces list.


For example, this action can be used to easily prevent negative volumes. Simply select every surface that is part of the desired model volume, ensure that the order in the subjects list is correct (i.e., equal to the order in the model volume definition), and choose to prevent overlaps above. The resulting surfaces will be strictly ordered, such that no surface crosses through and above any of the surfaces that are intended to be above it.


Intersection Dialog


The dialog is used to specify the inputs and options for the intersection actions. It is shown when needed for the actions listed above. Intersection will be performed after pressing OK in the dialog.


Subject Surfaces        Subject surfaces are listed on the left side of the dialog. It is pre-populated with any surfaces that were selected in the entity tree view when choosing the intersection action. Surfaces may be added, removed, or re-ordered (when applicable) in this list by using the buttons below the list.


Clipping Surface                When applicable, a clipping surface must be specified by choosing a surface in this drop-down box.


Direction                The two radio buttons are used to choose the direction of the action. The meaning and wording of these radio buttons varies depending on the chosen intersection action.


Output intersecting segments as new regions                When enabled, intersection profiles will be output along-side the intersection, just as if the Create Regions from Intersection Profiles action was performed afterward. Doing it here at the same time saves total computation time.


Output Intersected version of unmodified surfaces        Some surfaces (such as the clipping surface) will never have their geometry shape modified. However, it may be useful to output a copy of it that includes the proper intersection segments where the surface intersected the other surfaces. This avoids needing to perform the Fix Intersecting Geometry step afterward, in cases where it is required.


Remove non-overlapping triangles in subject surfaces        If checked, subject surface triangles that don't overlap the clipping surface will be removed instead of preserved (doesn't apply to all intersection actions).