SolidMesh: Automated Point Spacing

Tutorials

Automated Point Spacing

SolidMesh has a tool to automatically set point spacings based on curvature and local proximity. This tool is useful for many applications, but most often it is used as an initial grid for some sort of downstream application. For example, an inital mesh that will be optimized later but needs a reasonable representation of geometry is needed as a starting point. Instead of spending time setting individual point spacings, which could be time consuming if the model is large, SolidMesh has a tool to automatically set point spacings. The point spacings are then propagated to the edge grids and then to the surface grids. Below is an example of how to use this tool and the various parameters. Note: This tool only generates the edge grids and not the surface grids. Also, a very detailed report on the this algorithm can be found here Refer to it if there are any questions as to how the inner workings of the edge refinement algorithm works.

1. Read the file flying_minnow_clean.igs.gz in with gluing and trimming enabled. Then generate the surface grid by pressing and then . Then turn off the surfaces by pressing "1" to arrive at the picture to the right. Some of the points will not have a point spacing value and appear red, but ignore that for now. Those points were given a defaults spacing that gives the curves attached at least 11 points.
2. Clear the pick list by pressing the escape key, or . And press the autospace button and then . This will use the default values in the , , , , and . These default values have been determined through trial and error and are a good staring place for most applications. Let's now explore each individual parameter's effect on the final grid. From the image on the right, it can be seen that more points have been added to the leading edge of the wing because more curvature was detected there.
3. . The curvature ratio determines how many points will be put on curves in order to capture the curvature in the discrete grid. In general, increasing the curvature ratio will decrease the number of points on a curve. Also, decreasing the curvature ratio will increase the number of points on a curve. To demonstrate this, put a value of 0.01 (1/5 of original) in , press , and then to regenerate the surface grid. Decreasing the curvature ratio had the desired effect of capturing more curvature at the expense of more points.
4. For this step, set the curvature ratio to 0.5 in and regenerate the surface grid. In the picture, the tail or prop of the flying minnow can be seen. The consequence of increasing the curvature ratio is readily apparent. The sharp feature of the prop hub has been lost. This is because the NURBS curve that defines the hub is mostly straight and therefore the edge refinement algorithm missed the sharp feature near the end. Note: The original value missed this feature.
5. For this step, keep the value of the curvature ratio to 0.5 in . The value bound the edge refinement algorithm. The min spacing value is used so sharp features are not refined infinitely. The max spacing value is used to prevent spacings from becoming too large during the removal of superfluous points. Lower the value in to 1 and regenerate the surface grid. The prop now resembles the image in this step. The two highlighted points on the prop are 0.947026 apart. Use these two parameters to bound the edge refinement algorithm to ensure that the grid elements are not too big and not too small.
6. After the initial edge refinement, point spacing sources are put on edges in locations where the local spacing values deviate more than a factor of the value in . In most cases, this value will not be changed since it does not influence the mesh as strongly as the other three parameters. Therefore, consider the following mesh. The automated point-spacing tool was used to generate the edge grid and a point spacing source can be seen at the apex of the curve (red point). The point spacing needed at that location was not achieved by adjusting the end-point point spacing values. Therefore, a point spacing source was added to refine the curve in that location-the area of highest curvature.
7. The last parameter is . Its purpose is to alter point spacings on edges that are relatively close together. The parameter is relative since it is a ratio of distance away to local edge spacing. When the value in the field is negative (default) then it is ignored. However, when the value is positive then the following results are typical. Consider the following mesh that demonstrates, simply, two bodies that are in relatively close proximity: a sphere and a flat plate.
8. The mesh generated in this step was made by altering value of the proximity factor to 10. This alters the local point spacings on the grid so that they are at least 10 point spacings apart. The general result is a refining of the grid where they are in close proximity.