SKETCH!™ GEOMETRY: A Primer on Curves and Surfaces
Sketch uses two basic types of geometry: Curves and Surfaces.
• Curve: the Pencil, Curve-o-matic™, Circle and Square all create curves, which are infinitely thin and do not render. Adobe Illustrator 3.0® curves and DXF™ lines and polylines are also curves.
• Closed Curve: a curve where the start point and the end point are the same. To make a curve closed: A) draw a Pencil curve between its start point and its end point; or B) if two curves already touch each other near their endpoints, click with the Pencil at EACH end point.
• Curve on Surface: a curve created directly on a live Surface that remains attached to that surface. Only Circle, Square and Pencil can create these. To create Curve-o-matic curves near a live surface, create a sketching Plane tangent to the surface at the desired location.
• Isoparm (cross-section): any one curve across the mesh of an extruded or revolved surface can be selected and handled independently. Use option-click to select it. It appears black when selected.
• Basis curves: the original curve and the original extrusion path appear as black curves along the surface of Revolves or Extrudes. These curves can be manipulated to adjust the entire surface. These curves disappear if the surface is "puttied" or if an individual isoparm is manipulated, because the surface becomes Freeform and no longer maintains a construction history.
• Sketching Plane: the Plane tool creates flat, rectangular surfaces that are used as guides only. They are not part of your design and are never rendered. They appear in the 3D view as cyan (default - may be changed) squares when not selected.
• Surface: a spatial mesh with no thickness that renders with the material assigned to it.. This is shown as a red (when selected) mesh that represents the entire surface. Changing its smoothness changes the density of the mesh.
• Revolve & Extrude: surfaces that maintain construction history, ie. they remember how they were built.
• Freeform surface: A surface without construction history, such as a Revolve or Extrude that has been "puttied."
• Cap surface: the surface automatically created at both ends of a revolve or the extrusion of a closed planar curve. A Cap surface cannot be directly manipulated, however, selecting the isoparms at the end of the surface will adjust the cap. Note that the Cap surface must always remain planar, so if the surface is twisted, the cap may not be able to match it.
• Polygonal Surface: a flat surface bounded by straight lines. These are imported as Upfront objects or DXF faces. They appear as black outlines when not selected.
• Seam: the heavy red line on a revolve or extruded closed curve. Puttying the surface by selecting a point directly on the seam allows the surface to be split open.
• To produce a Freeform Surface from a Curve: use Extrude, Extrude-o-matic or Revolve.
• To produce a Freeform Surface with Cap: as above but make sure the curve is planar, and closed.
• To produce a Polygonal Surface or Cap surface: Create a closed planar curve in the desired shape, Extrude it and delete the extrusion (option-click to select) and the EndCap. NB: Ensure that you have set the Smoothness of the extrusion before you delete it. When a Cap surface is no longer attached to an extrusion, its smoothness can be altered.
• To produce a Curve from a Freeform Surface: Select the desired isoparm (option-click) and choose Duplicate from the Edit menu: this creates an exact copy of the selected isoparm.
•If you have a 24 bit (millions of colors) display adapter, Sketch! will refresh the screen very slowly. Setting your monitor to 8-bit (256 colors) for modeling is recommended. Images are rendered in 24 bit color.
• You cannot extrude a surface that has already been extruded. You can modify the basis curves (cross section and path) to change the entire surface, or Duplicate any cross-section and extrude the new curve to continue an extruded surface.
• When one side (or face) of a cube is "live," you cannot immediately make another side of that same cube "live." This occurs only with Imported cubes or objects created with the Cube tool. To make a different side of a cube "live," first make another plane or surface "live," then make the next face of the cube "live."
• It is sometimes difficult to pick an object whose Smoothness is set to Roughest. Pick these objects in the Assembly View, or by clicking directly on the vertices that are displayed.
• To ensure precise erasing, either zoom in closer to your work, or erase more slowly.
• You can continue a Curve-o-matic curve by clicking on the end of a selected curve, but the Curve-o-matic tool joins curves differently from the Pencil tool. The Curve-o-matic tool can only join existing selected curves, one at a time. It cannot be used to close an existing open curve. Use the Pencil tool to close open curves.
• The Curve-o-matic tool can only be used on live sketch Planes. When Gravity is on, creation of Curve-o-matic lines is restricted to the bounds of the live plane, regardless of the selection in the Gravity Settings dialog.
• You cannot use Extrude-o-matic for multiple simultaneous extrudes.
• You cannot use Extrude for multiple simultaneous extrudes unless the extrude path is perpendicular to the live Plane.
• Curve-o-matics and Extrude-o-matic always use the "live" surface while Gravity is on, even if "Use Live Surface Only" is not selected in the "Show Gravity Settings" dialog.
• When you select the "constrain" checkbox in the Get Info dialog for an object, you are only constraining the object while the Get Info dialog is open. When you close the dialog, manipulating the object is not limited in any way.
• You cannot change the shape of a cap, cube, or polygonal surface using the Putty tool. These objects must remain planar. Caps can be altered by changing the surface they are attached to, however if you alter the surface so that the cap is non-planar, it will no longer be attached to the surface.
• Sketching across the seam of a cylinder, sphere, or other closed surface produces unexpected results. To prevent this, rotate the object, or sketch the new object so that it does not cross the seam of the surface (visible as a thicker line).
• You cannot Undo an object scaled via the Get Info dialog.
• After a cusp is added to a curve using the putty tool and the Command key, performing an Undo command will undo the manipulation and restore the curve to its former shape, but it will not remove the (now-invisible) cusp in the curve.
• To mirror an object, use the Handle tool to scale it by -100 per cent along the desired axis, or choose Get Info, and type a minus sign in front of the desired dimension(s).
• To partially Revolve an object, first Revolve it fully (360 degrees), then select the revolved object, choose Get Info from the Edit menu and type the desired number of degrees into the dialog box. This must be done before Puttying, while the object still maintains its construction history.
• If you Copy an object from one design, Close it and Open another, then Paste your object, the object may lose its Material assignment and be reset to the default.
• Sketch! assumes that whenever units are changed, the workspace will be converted into its equivalent in the new units. We recommend that you do not change units in the middle of a session.
• When two monitors are in use, in certain cases you may experience an incorrectly refreshed window. Clicking in the zoom box at the upper right corner of the Sketch! window will force a refresh.
• On page 4-7 and 4-9 of the Sketch! manual, the "Save As..." EPSF information is incorrect. EPSF image and geometry files are stored without a preview image, and you will not see a dialog asking you to choose the type of preview.
• Color information is not included in a DXF file.
• You cannot use Import to get data from a Catalog file, as these types of files are not complete StyleGuide files. They should be Placed using the Catalog dialog.
• If you use Import to read in a StyleGuide file, you may get duplicates of the rendering qualities, materials and backdrops in your design. Use Open to read in the desired StyleGuide file.
• When Sketch! loads, it reads a file in your Preferences folder called "Sketch!™ Prefs". If you want certain sizes, qualities, materials, etc. to always load, you can create a design with those settings and save it in your Preferences folder, or open the Prefs file directly, make the desired changes, and Save.. It must be called "Sketch!™ Prefs". (The ™ character is obtained by pressing Option 2). To reset the Prefs file to the defaults, throw it away and Sketch! will create a default file upon startup. You may also edit this file directly using a text editor. Refer to the StyleGuide Reference document for more information.
• When exporting DXF files destined for AutoCAD, you must ensure that the name ends in ".DXF", as AutoCAD will not recognize the file without it. Sketch! replaces any extended ASCII characters with that character's ASCII code, because AutoCAD cannot read some valid Macintosh characters.
• The Sketch! Assembly view shows a design imported via DXF differently than the same design created in Sketch. This reflects certain assumptions that the DXF format makes about the organization of groups within the design.
• Non-planar polygons in Upfront file format are ignored when importing into Sketch!. When exporting objects containing non-planar polygons from Upfront, export the objects as DXF, and import them into Sketch as DXF. The non-planar polygons will be broken into several planar polygons, and will render correctly.
• When Navigating with the viewpoint very close, the bounding box seems to disappear. In fact the bounding box is always present, but possibly beyond the physical limits of the screen. Either continue navigating around until an edge appears or choose "Fit to View" to reorient your location in 3D space.
• Wireframe objects are clipped when farther away than 10,000 units. They will not be displayed. Do not set the view farther away than 10,000 units.
• Your views are part of the World assembly and cannot be grouped in an Assembly with objects or lights.
• To pick at the lowest level of the hierarchy (eg. the individual curve rather than the entire object, or the individual object rather than the group), press the Option key as you select an object in the 3D space (without the Option key, the entire assembly is selected). Open the Assembly View to show this more clearly.
• If a curve is extruded and crosses over itself, the renderer may become confused about which way the surface is facing, and shade the facets incorrectly. This will be visible as black streaks on the rendered surface. You can avoid this by creating the curve segments of the Extrude-o-matic surface tangent (start angle 0.0) when extruding.
• Sketch! checks coincident line segments to prevent rendering them as "crossover geometry". If two or more line segments are coincident, but of unequal lengths, you may experience incorrect shading.
• If a system error occurs while you are attempting to save an image file, Sketch! saves the image in a locked file named "~~Sketch!_SaveAs_Temp". If this occurs, unlock this file and rename it. This makes the temporary file again available for use.
• To determine if rendering has completed, click on the File menu. If the menu item reads "Render", then the rendering is done. If it reads "Stop Render", the rendering is still continuing. To visually track the progress of the rendering, you may want to use any non-white backdrop. This way, you can see at a glance how far the rendering has progressed.
• You cannot interrupt the Material or Catalog dialog windows "Update" once it has begun.
• To apply Refractions to transparent objects, you must select Ray Tracing in your Render Settings dialog. The refractive materials water, glass and diamond are provided in the default Material Catalog. Other refractive values must be typed directly into StyleGuide files; if you are using a word processor, save the file in its "text only" format. Values for common materials are given below:
• When rendering with texture maps, if a large texture map is applied, and there isn't enough memory to render using that texture, the texture will not be applied. Texture maps should not contain more detail than will be visible at the selected resolution. Use a smaller texture map, allocate more memory to Sketch!, or set the smoothness of the object to a lower setting. In some cases, resizing the modeling window to its smallest area before starting to render may free up more memory for the renderer. The maximum width that can be rendered by Sketch! is 4094 pixels.
• The rendering frustum (viewing pyramid) has a maximum width of 165 degrees.
• When polygonal shadowcatcher surfaces are rendered via scanline (non-raytraced), the edges of some surfaces are visible as a faint shadow. Also, if a light casts a shadow over the whole of a shadowcatcher surface, it may be visible as a faint shadow.
• When simulating an orthographic view, and placing the camera about 7000 units away, a slight vertical/horizontal shift in the rendering will be visible, ie. it will be off a little from the modeling view.
• The Delete key is disabled when Preview is active. If you want to delete an object that is being previewed, use Clear instead.
• When using Sketch! for long periods of time, or after deleting large numbers of objects, the memory that Sketch! uses may become fragmented. You may not get the "Running low on memory" message, because there is still memory available, but all of the large blocks may be fragmented. If Sketch! slows down dramatically all of a sudden, Save your document, Quit, and start up again.
• Sketch may be unable to locate the image required when browsing over the network to another Macintosh: you can locate the file on that Macintosh for Sketch and continue; or, preferably, you should make a copy of the material and the image on your on Macintosh and refer Sketch to that location.
