View a video
that will show you the different rendering options in Maxsurf.Rendering a surface can be used to display the shape and fairness of the surface. Maxsurf has different rendering types available. Each rendering type can be used for different purposes. See also: Perspective Window on page 36.
View a video
that will show you the different rendering options in Maxsurf.
Maxsurf has four different ways of calculating and rendering curvature on a surface. You control these settings using the Rendering command from the Display menu. Render may only be selected when the Perspective window is active.
To display the rendered view, turn on hidden surface elimination. It is then possible to display a shaded view of the design, or to use false colouring to highlight the curvature of the surfaces.
Selecting Hidden Surface Elimination performs surface shading over the surface, using a fixed light source. If Smooth Shading is selected, the base colours of the surfaces are those chosen in the Appearance option from the Surface menu.
Shading using polygons is utilised. Surface contours may also be displayed with this option.
An alternative shading algorithm is used to provide smoother rendering. The colours of the surfaces may be changed in the Appearance dialog.
To examine the fairness of your design, Maxsurf can use false colouring to display four types of surface curvature. These have different uses and are described below:
Is the product of the maximum and minimum curvatures at a point on the surface. Gaussian curvature will indicate whether the surface is locally elliptical (positive Gaussian curvature, i.e. both curvatures in the same direction), whether it is hyperbolic (negative Gaussian curvature, curvatures with opposite signs i.e. saddle shaped), or whether it is developable (zero Gaussian curvature).
Gaussian curvature is a useful indicator of areas of twist in a surface, but is not directly linked to surface fairness. It is possible for a surface to be quite unfair and still be developable, yet the Gaussian curvature display will not reveal any problems.
Gaussian curvature can be used as an indication of whether a surface is developable. A developable surface is one that can be formed out of a flat sheet material by bending or rolling, without stretching or distorting the material. In this case, the surface will have a Gaussian curvature of zero at all points; i.e. the surface is only curved in one direction and straight in the direction orthogonal to that. See Surface Types in Maxsurf on page 80 for more information on what developable surfaces are and Generate Markers for Developable Surfaces on page 206 for information on how to model developable surfaces in Maxsurf.
You can adjust the brightness value to make the display more or less sensitive to the Gaussian curvature values. See Brightness Level on page 94 for more information.
Note:
The Gaussian curvature gives an indication of developability, but should only be used to isolate
areas where the plate will be less developable.
If you want to be certain of a plates’ developability, load the surface into
Workshop and develop a surface plate. You can then examine the strain
distribution on the plate; the plate is developable if there is no strain. A
small amount of strain can be acceptable dependent on the builders’ plate
bending equipment and production techniques.
See the Workshop manual for more information, especially regarding precision
settings during plate development.
This is a display of the curvature of each longitudinal parametric curve, taken perpendicular to the surface at each point along the curve.
This display is extremely useful for determining the longitudinal fairness of a design. You should look for an even graduation of colour along the hull. Inflections can be detected by looking for changes from blue (positive curvature) to red (negative curvature). If you choose to show positive curvature values only, do so by using the following settings:
This will reveal areas of negative curvature by painting them black.
Is the curvature of each transverse parametric curve, also taken perpendicular to the surface at each point along the curve.
This display is extremely useful for determining the transverse fairness of a design. You can mask off areas of positive or negative curvature in the same way as with the longitudinal curvature display.
The convexity check highlights any areas of negative curvature.
The convexity check calculates and displays the minimum curvature for each point on the surface. If this minimum curvature is less than zero, the surface is locally concave.
Note:
Before you use Rendering, make sure that you have set the direction of the Outside Arrows (see page 87). When the Outside arrow points outwards, positive curvature is displayed as blue and negative curvature as red.
The brightness level referred to in the dialog affects the way in which the colours in the display are mapped onto the curvature values.
Because the range of colours is small and the range of curvatures infinite you may need to change the colouring to suit the curves you are looking at. Changing the brightness level re-maps the colours - if the image is very dark and it is difficult to distinguish different curvatures, try using a smaller number. On the other hand if the image tends to be all pale colours, try a darker tonal value.
For Gaussian curvature, a higher brightness level will make the display more sensitive to non-zero Gaussian curvature, highlighting more areas. See Curvature Display Using Rendering on page 92 for more information.
Smooth shading rendering uses OpenGL. To take advantage of the OpenGL rendering capabilities you should select this option in the Rendering dialog.
OpenGL requires suitable driver software to run correctly. The driver required depends on the operating system and video card you have on your computer. The driver is normally supplied by Microsoft, or the video card or video card chipset manufacturer. Occasionally there may be problems with the driver, which prevent Maxsurf from rendering the image correctly or may even cause the computer to crash. This is more likely for very new video cards and/ or new, or less popular, operating systems such as MS Windows 2000 or MS Windows NT. This is because the drivers will have had less testing. If a problem occurs, one way of helping to determine if the driver or Maxsurf is at fault is to try running other OpenGL software such as the OpenGL screen savers; if the OpenGL screen saver crashes, the problem is probably with the OpenGL driver and you should try to update it. Video card manufacturers regularly update their drivers and these are normally available from their web sites. Another web site, which can be very helpful, is: www.opengl.org.
When this option is selected, it is possible to select a rendered surface. This brings up the surface properties in the Properties Pane. You can also use the right-click menu to trim, lock or delete the surface etcetera.
When there are several surfaces directly behind each other, a Select option will appear at the bottom of the right click menu which allows you to select which surface you wish to select.
The colour of the selection highlighting can be set in the View | Colours dialog.
When this option is selected, the control point net is displayed in the rendered surface colour. It may be desirable to set the surfaces transparency to for example 30% to avoid a control point being hidden by the rendered surface.
Colour coded control points.
Maxsurf allows the user to edit the lighting settings used in the Perspective window when rendering is turned on.
Light Positions
Maxsurf has the option to use four different light sources. These can be turned on and off by clicking in the Render toolbar.
It is possible to vary the location of these lights by editing values in a lighting dialog. This dialog is displayed by clicking on the right most icon in the Render toolbar when the Perspective window is active and rendering is turned on.
Each light is specified by three values, distance, bearing and elevation. Distance is measured from the centre of the view in the perspective window. Bearing is taken relative to the direction from the eye to the object being viewed. For example, a light at 0 degrees is pointing in the same direction as the eye is looking at the object, 90 degrees is to the right of the object, -90 degrees is to the left of the object and 180 degrees is behind the object. Elevation is in degrees above the horizontal. A negative elevation value defines a light shining up from below the horizontal.
Light Intensities
Ambient, Diffuse and Specular values define what kind of reflection will be seen on the surface. If only ambient light values are specified, the object will be lit evenly from all directions and its reflected light will not appear to change in brightness as it is rotated. This is analogous to the sort of light seen on an overcast day. The result is no differentiation of colour or brightness across the surface.
Diffuse light is directional but is made up of parallel rays. The effect on an object illuminated with a diffuse light is that it changes in brightness as it is rotated due to the change in the incident angle of the surface.
A specular light is one that comes from a specific point such as a light bulb. When an object is lit with specular lights, definite highlights will be seen moving across the surface as it is rotated.
In practice, the ideal combination seems to be a small amount of ambient light, and roughly equal contributions from the diffuse and specular lights.