Repair: Polygon Corrections

Viewer Interaction

Some of the functions described below can also be directly applied to one of the bodies by clicking on the body in the viewer and then using the right mouse button to bring up the sub menu. Here the options are to: Split Body, Delete Body, [Delete All Others], Fix Normals, Flip Normals, Close Holes, Check Body (for All) or Change Color.
What is special with this (unlike the tool buttons discussed below) is that each option only acts on the selection and that there are two additional options, to Delete the selected Body, the Delete All Other Bodies and to Flip Normals of the body. This last option allows all normal vectors to be reversed from their current orientation (without consideration of whether either is correct). Note that inside/outside of a face is identified by the color with the inside being a dark grey.

Repair Tools: Overview

The following is a brief overview of the tools available on the Repair Tab. Several of these have additional details on their operation discussed on a dedicated page, linked with each item.

Issues

Clicking this button will perform an evaluation of the data loaded. The Issues button is a toggle-on/off option. Five main items can be evaluated from this option:

Open Edges

Upon clicking the Issues button, any edges that are used by only one face (boundaries of the body) are identified and the total number displayed. Checking/Un-Checking the box next to the item allows these items to be hidden from the immediate view. Since open edge detection is a quick process, it is always shown when Issues are to be displayed.

Invalid Edges

Invalid Edges are those that are used by more than two faces. This indicates that there is a discontinuity across the faces as the neighboring face to a given face is not uniquely identifiable. These errors require correction.

Duplicates

Duplicate faces can indicate an issue whereby neighbor information for a given face cannot be obtained. These items need removing and attention needs to be paid to where these occur and whether their removal is warranted and acceptable.

Invalid Features

Invalid Features (Faces) are those that do not correctly define an area and are likely ones where multiple points of the face have been collapsed either onto other points or onto one of their edges. The result is that the face does not have an area and therefore does not have a front or back surface. These items need to be removed; in some cases they can automatically be healed.

Intersections

Intersections of faces with other faces are automatically checked when the Issue button is pressed - though this behavior can be modified. In general, the process is quite efficient and finds any cases where two or more faces intersect. Evaluation of very large files can take some time, so if this test is not desirable in all cases, the Settings>Application Settings>Repair: AlwaysComputeIntersections value can be changed to False in which case intersections are only evaluated when first toggled on.

Invalids

The Invalid Removal tool finds and removes (where possible) items that are defined as Invalid Features in the Issues display. There are two additional options provided: Spit and Move as well as Project Split which attempt to separate facets where too many facets share an edge and facet splitting where vertices overlap edges, respectively.

Duplicates

The Duplicate Removal tool searches for Faces that are present more than one time (defining the same three vertices) and removes all but one of their instances. The orientation of the remaining facet is not considered as the tool does not distinguish between facets' orientation, only their corners.

Normals

The Normal Vector of a facet/triangle is defined by the order in which the corner locations are used. It is possible that some or all of them point inward rather than (correctly) outwards from the body. This tool attempts to redefine the orientation of any that are pointing in the wrong direction though this is based on the overall layout. This means that it is, in some cases, possible that all normals become incorrectly (though consistently) oriented and require all of them to be manually reversed (see above for how to flip them).

Stitch

The Stitch option attempts to correct close proximity surfaces with edges that are otherwise only used by one face. This tool should be used in cases where the data does not accurately define a continuous surface across edge boundaries (perhaps due to tolerance issues, rounding or data being generated on a per-face basis). Usually, this scenario occurs when an application is used to generate the original surfaces that does not enforce continuity across adjoining surfaces.

Merge

The Vertex Merge tool allows locations within close (but not identical) proximity to each other to be re-assigned a location based on a tolerance value. This allows data that does not contain accurate tolerance information to weld together.

Overlaps

Overlaps are regions identified in the Issues page for the Intersections. These are facets where two of more items intersect each other. This repair tool attempts to correct the issue by splitting any involved facets using the neighboring facets as a boundary. In general, the result is simply that the surfaces become continuous though the involved edges will likely become sources for the Invalid Edge issue and need to be handled separately. Usually, this helps as way to prepare the issue for further (manual) correction and perhaps splitting and deleting of the resulting bodies. This tool should not be considered as a way to resolve the issue in a single step, but rather as part of a longer process of identifying and resolving issues.

Fix Holes

Hole fixing works by finding open edges (those that are attached to only one face) and to then generate new faces to close the edge loops together, using one of several options. If bodies consist of shells (such as generated by 3D scanners where only part of the body was scanned), this option should not be used, rather the Thicken tool should be considered.
The usual case where hole-fixing is appropriate is for cases where circular features (screw-holes and similar) were removed.

Auto Fix

There are different levels of Automatic repairs that can be applied. These are in no way intended to capture and resolve all issues but merely to capture and process more common items that have a repair solution that can be automatically applied. Some of the available tools also approach the issue from the perspective that the original data should only be considered as a approximate source and to generate a completely new set of surfaces.

Wrap

The Wrap tool can in some cases be used to generate an approximate representation of the original data for cases where the original set is not usable. Two different approaches are implemented, one where the original data is resampled at an axis-aligned bounding box location and then a new set of surfaces generated from these locations, the other by only considering known points and orientations of the surface and to then re-create the surface by means of a point-cloud approach.