Geometry creation#
Description#
The GEOM command is used as a very minimal CAD system with a simple
automated mesher and mapped meshing capabilities. This is essentially
the basis of Zebulon pre-processing. You can import IGES files into the
geometry mode to start a model by starting the application with
file.iges as a startup parameter.
Set Grid#
Set Grid is used to set the click to grid property, and also used to alter the mouse click plane to allow 3D editing. Mouse clicks will always be projected onto the active mouse click plane to define a selected spot. If the snap to grid parameter is selected, the click point so projected will be adjusted to be on the closest grid point. The clicking plane corresponds to \(z=0\) initially. Some commands are based on points (e.g. line between 2 points), and if a point exists in close proximity to the click position, that point will be chosen. The click projection only applies when a point is not found close by, or if click dragging of a point is used (to modify position).
There are some parameters for this command on the Set Grid dialog:
Grid Spacing: The spacing in real coordinates of the visible grid.
Click Steps: The number of steps which can be clicked at per grid line.
Center x y z: The center position of the click plane. This is the reference for the grid lines, and also can be used to set a depth to the click plane (e.g. 0. 0. -5).
Additional options are as follows:
View Selection: Allows quick selecting of the X, Y, or Z plane as the click projection plane, or selection of an arbitrary plane by use of three points. It is very useful for this later option to create points beforehand with the point select command using exact values (typed in).
Show Grid Axes: Show the active click projection plane coordinate axes in red.
Show Grid Lines: Show the grid lines.
Click to Grid: Clicks are moved to the closest grid click point after being projected onto the click projection plane.
Points#
This command is used to digitize points in the geometry space. It allows click creation with the left mouse button in the main drawing window, or by entering exact values for the point coordinates in the dialog window. Note that all geometrical entities are in 3D at all times. After creation of lines, arcs or curves, unattached points can be cleared using the Tools\(\rightarrow\)Delete Free Points menu item.
Lines#
The lines command creates line segments between points, or as a pre-defined structure (rectangles). The lines are point based, so when creating a line some point selections are required (differs depending on what type of line option was selected). There is a selection radius about points which makes the preference selection of pre-existing points. If there is no pre-defined point within the “click radius” (actually a cylinder extended into the view direction), a point will be inserted according to the settings of the view grid.
dX dY dZ: The line lengths projected onto the X, Y, and Z coordinate axes. These values are used when the 1pt, dX dY dZ mode is selected.
1Be careful to check that there is only one line between any two
points. selecting a doubled up line will not be highlighted through
the entire line distance.2 Points: Create a line between 2 points 1Be careful to check that there is only one line between any two points. selecting a doubled up line will not be highlighted through the entire line distance.. Select 2 points to connect with a line.
1pt, dX dY dZ: Creates a line using the line vector components, starting at a selected point.
Rect 3 pts: Create a rectangle from 3 points. The first 2 points determine the corners of one side, and the 3rd point determines the length of the 2 sides connected to the first line, in the current selection plane.
Circle#
Arcs and circles are created with a transformation matrix to localize the circle to the current click projection plane 2note that’s not necessarily the view plane.
theta 1,2: The starting and the ending angle of the arc when using options Arc Center, a1, a2.
radius: The arc or circle radius.
Circle, Center, R: enter the radius and click on a point, or click to create the center if there’s no point nearby.
Circle, Center, point: Click on the desired center point, and a second point where the circle radius is the distance between the two points.
Arc, Center, a1, a2: An arc defined by a selected center point, and created immediately with radius R and angles theta 1 = start and theta 2 = end from the text entry boxes.
Arc, Center, pt1, pt2: An arc centered at a selected point, with radius calculated from the center and 2nd click spot, and end angle figured from the last selected point (3 selections total).
Arc, 3 points: An arc passing from select point 1, to select point 3, while select point 2 is used to find the radius. The selections should be counter-clockwise in the path of the arc.
Curves#
Curves can be created with a variety of means, and imported as NURBS curves from IGES files 3Currently the curves are rather poorly implemented, but will soon be improved. The Bezier and B-spline by points options are not yet available.
Parametric Cubic (4pts): Select the 4 points of a parametric cubic spline. Watch for extreme distortions of the curve, as the algorithm just fits the curve exactly representing the selected points, and not a smooth interpolation of them.
Bezier: Bezier curves.
B-Spline (by points): B-splines as interpolations of points on the curve.
B-Spline (by ctrl pts): Click select the B-spline control points exactly (which are not on the curve except for the 1st and last points).
Move/Copy points#
Points can be diplaced and copied using the displacement vector (dX, dY, dZ).
Move point: Give the wanted displacement vector (dX, dY, dZ) and click Go. Then, select the points to move.
Copy point: Give the wanted displacement vector (dX, dY, dZ) and click Go. Then, select the points to copy.
Divide Edge#
Edge divisions are useful in meshing, and building up geometries. In particular, in order to define a “sense” to an internal boundary of a mesh region (domain), 3 or more segments are advisable. If the internal boundary is a circle for example, the sense of the internal boundary can be made by splitting the circle into 3 arcs and selecting them in the correct order (clockwise for an internal boundary). Not all edge entities may have the division implemented.
Num: Number of segments to create.
Progression: Geometric progression of the cuts, starting from the closest end to the selection point on the edge.
Fillet#
The fillet command is used to clip and fillet intersecting edges 4This is a general algorithm for arbitrary 3D and therefore does not allow for specific solutions which may exist analytically (such as a circle intersecting with a line). These cases will be added shortly..
Cut both: Clip intersecting edges where the side kept is the side containing the closest selection point to the respective edges. The intersection point can usually be outside the bounds of the original edges, at which point one or both of the edges are extended.
Divide Both: Divide 2 intersecting edges at the point of intersection with a point inserted.
Fillet in Cut: Clip the 2 intersecting edges as above, and alter the lengths so an arc of given radius (in the R text field) can be placed in the intersection, with the arc being tangent to both edges at the new edge end points (valid only for lines).
Local axis#
This command allows users to define a local axis in order to easily create geometries.
