KernelCAD Documentation

Start your model design by identifying structure of you model: How many objects it will have and what type of objects. Objects normally represent different parts in the mechanism or other entity which is being modeled.

When modeling with a Generic 3D Object, start by determining orientation of the local axis (local z-axis) of the object. Normally axis of the object points in direction in which the object has the longest dimensions, or with respect to which the object is the most axially symmetric.

It is also useful to position origin of the local frame at approximate center of the model. I should be easy and natural to rotate the object around the origin of its local frame. Relative position of an object and its local frame can be changed at any time using "Current object">Modify submenu. Note that these two operations are not designed for moving objects (use the Current Object Page instead) it is rather for changing handle on the object for more convenient rotations.

Modeling should start from lower dimension up. In a 2D view points should be modified first, than arcs because modification of a point generally changes curvature of adjoined arcs. Similarly Base knots, edges and patches is the preferred sequence of modifications.

Handling validation restrictions

The most common difficulty in modeling surface of an objects is dealing with rejection of invalid modifications. When software detects that as the result of the last action (edit box change or mouse movement) some of the patches in the object will become invalid it stops the change possibly with display of message on the form.

To avoid above problem we suggest the next sequence of modeling:

Start modeling complicated curved surfaces by using initially only flat type of patches and straight edges.
Set correct position of ends of 3D line segments ( edges of Patch Strips) at each knot.
Change 3D line segments to curves where necessary and set correct curvature of each 3D line segment.
Change patches which should be curved to Arc Patch type and adjust its curvature.
If you can not achieve desired shape of the surface on the last step due to rejection of invalid geometry, add more patches to the object using Break and/or New knot commands.

The main reason for invalid geometry is that some of 2D arcs in the model can become invalid. It happens when :

An end of the arc after the modification located too far for the current radius of the arc
Radius of the arc has become too small to be able to connect ends of the arc.

Both these cases can be expressed by condition of validity of a 2D arc: Radius of an arc must be at least half of the distance between its ends.

Sometimes it is not easy to detect which arc is being rejected. To find it, have a look at the both 2D editors first. Arcs which are full half circle normally reject their further modifications. We call such am arc Full Arc.

If there no such an arc, move the cross-section position through the whole range while watching Cross-section View. If in some position one of the arcs becomes full - this is the problem. Reduce curvature of the arc or add additional Patch Strip by using Break command. If this is the Profile View use the New knot command instead.

If you can not find a full arc by above methods switch to wire frame view and inspect all 3d lines.

If this does not work try to reduce curvature ( or even change it to flat ) of the most curved patch around the area which you are attempting to modify.

In a hard case, detect the most difficult patch, make it flat and modify all other patches. Change the problem patch back to arc again, select it in Cross-section View. Profile View will display its curvature (or radius). Select the arc which is correspondent to the patch in Profile View and open its Properties dialog using context menu (right mouse button). This particular dialog does not do immediate validation of entered values. Type correct values for curvature of this axial arc, enter also required values of curvature (radius) at adjoined knots and press OK or Apply.

If nothing works, submit a Support Request to DInsight with the model included, and take a break.

Folded surface problem

Some modifications of surface patches can lead to situation when a single patch intersects itself (A flat patch screwed by 180 degrees). This is considered invalid geometry. Software does do anything to prevent the situation. In some cases the software will still work but sometimes it will cause holes to appear in the surface. Correction of the geometry should remove the defect.

Another aspect of the same situation happens when edges which are supposed to converge at the last or the first knot actually are slightly shifted against one another creating a nearly invisible folded area. Good indicators of this situation are either black or white spots on the surface near the convergence point. Switch to wire frame and use zoom to examine the geometry. It is recommended to use edit boxes from the form or dialogs to enter exact positions of ends of edges.

Although making edges of patch strips to converge or coincide is valid and useful technique it is recommended to avoid situation when different edges of the same patch intersect each other in a middle point.

Smooth Patch Joins

"Smooth surf Join" check box, which appears when a common edge of two patches is selected can create incorrect lighting (black or white spots) of the surface around the joint if its status is significantly different from the actual geometry of the surface. Try to change status of the check box and see if it improves appearance of he surface in 3D.

Singular Patches

In some abnormal situations like folded surface described above the surface can have some anomalies like white or black patches. In this case Incrementing or decrementing geometric resolution (Current Object menu > Options) often resolves the problem.