Introduction

MeshView is a graphical analysis tool for displaying, analyzing and editing 3D unstructured tetrahedral meshes. It is designed to allow users to visually verify the integrity of a mesh. There are two separate approaches we take to the problem. The first provides for manipulations of the mesh, allowing the user to verify the overall structure of the mesh. There are three techniques that we provide: a growth algorithm, clipping isosurfaces, and multiple views. For the growth algorithm, the user picks a starting tetrahedron, and then can grow the mesh out, level by level, where a level is defined by all those elements that share a face with an element on the previous level. With the clipping isosurfaces, unlike traditional clipping planes, if the plane goes through an element, than the entire element is discarded, instead of drawing partial elements. Lastly, the user can have several different views of the mesh, with an orientation window to show how the views are with respect to each other.

The second approach is to look at quantitative measures of the mesh, like volume, aspect ratio, and error. To study these, we provide an interactive histogram that displays number of elements per value. The user can then move two bars to specify a range of values, and all the elements within that range are displayed.

To accommodate the user's need for fixing problem areas once they are found, we also provide several editing options. The user can add a node in the center of an existing element, thereby subdividing that element, or she can delete either the four vertices of an element or a single vertex.

Creating a map

Like all modules in the SCIRun environment, the MeshView needs to hooked up with various other modules to create a working map. The following is a general use map for using the MeshView program.

The MeshView module has four ports, two input and two output. The two input ports are for (a) a mesh and (b) a colormap, and the two output ports are for (c) a geometry viewer and (d) a mesh writer. Ports a and c are required. The mesh input can be from a variety of modules, however. The simplest is just a MeshReader which reads in a pre-existing mesh. Other modules could be a Delaunay module which creates a mesh given a point set. The geometry viewer, Salmon, is also necessary for viewing the mesh while interacting with it. The colormap module, GenColormap, is for defining the colormap used when viewing the quantitative measures. Finally, port d is for writing the mesh to disk after it has been edited. There are two different modules that can be used, MeshWriter which writes a mesh in the SCIRun format, or TetraWriter which writes a conventional point file and tetra file. NOTE: the output mesh module should not be used until all editing is complete, to save time by not having the mesh written every time there is a change.

Interface

MeshView is controlled through its user-interface, as shown below.

The MeshView interface is divided into 7 different sections.

Section A

The first section lets the user specify which technique she wants to do, either manipulative, quantifying, or editing. Only one technique can be used at a time.

Section B

The second section allows the user to specify whether the geometry should be rendered in ``production'' or ``normal'' mode. In production mode, the mesh is rendered with cylinders that are suitable for using as final images. Normal mode renders the mesh as either a wireframe or Gouraud shaded. For the production mode, there is a slider that lets the user set the width of the cylinders.

A mesh rendered in: a) normal mode and b) production mode.

Section C

The third section contains the buttons and sliders for the manipulative techniques. The first slider is for setting how many levels the user wants to look at. Following that is the switch to indicate whether the user wants to look at all of the levels up to the specified level or only the outermost level. Due to the way the program only sends surface faces to the renderer, there needs to be a way for the user to see the entire mesh when she changes to wireframe mode. Therefore, the third button provides the user with the capability to flip between rendering the entire volume, and rendering the surface only. This switch is only useful when rendering in wireframe mode. The next three sliders are for manipulating the clipping isosurfaces. These sliders permit the user to make a ``cube'' of clipping isosurfaces and thus able to clip from any orthogonal surface.

Section D

The next section is for the quantitative measures. There are two different ways of displaying the elements that fall into the desired range: either only the elements in the range will be displayed, or those elements will be displayed with the rest of the mesh drawn in wireframe. The first switch allows the user to toggle between these two options. The second switch is for indicating whether the user wants to see the elements that are inside of the range or outside of the range. Choosing the elements outside of the range displays both the largest and smallest valued elements at the same time. The last four buttons are for selecting a measure, either volume, aspect ratio, size versus neighbor, or error.

Section E

The editing capabilities comprise the fifth section. There are three editing options: adding a node, deleting an element and its four node, or deleting the node nearest to the cross-hair picker. The element to be edited is selected by moving the cross-hair picker into the desired element.

Section F

The sixth section is a switch for indicating whether the user is using the cross-hair picker to select a new seed element or an element to be editted.

Section G

The last section shows information about the mesh, including the number of nodes, number of elements, and quantitative information about both the seed element and the element selected for editing.

Picking an element

There are two techniques in the MeshView program that require picking an element in space. To accomplish this, a 3D Crosshair Widget is used. Briefly, to select an element, you hold down the SHIFT key and then use the left mouse button to select and move the widget. The selected element is the one which contains the center sphere of the widget.

Example of the crosshair widget inside of an element.

Histogram

The interactive histogram allows the user to specify a range of values to indicate which elements should be displayed.

The two red bars on the histogram are movable and define the range. The lower lefthand corner displays what the range is numerically, making it easy to get an accurate range.