INTRODUCTION

Cross-sections are integral to the creation of many types of models in RDS. The manual mentions that files can be imported for use as cross-sections and gives some basic steps, but provides few details as to how to create and import them.

Cross-sections can be acquired or created in a variety of ways:

1. Create them directly on the drawing plane in the RDS Free Form Modeler.
   
2. Create them in a vector drawing program.
   
3. Create them in a raster (bitmap) drawing or photo-editing program and convert them to vector format using a raster-to-vector conversion program.
   
4. Scan them from drawn or printed material into a bitmap photo-editor and do the conversion to vector format.
   

   This discussion will cover the creation of cross-sections in either a bitmap or vector editing program, the conversion of bitmap (raster) files to vector format, and the import of the cross-section into RDS.
   
   I. BITMAP vs. VECTOR PROGRAMS

   The first thing you need to understand is that there is a difference between bitmap (also known as raster) files and vector files. Bitmap files create an image by storing a mosaic of many individual bits of color. Vector files create an image by mathematically projecting paths from one point to the next on the screen. It’s the difference between drawing a line by lining up colored chips, versus writing a mathematical formula to describe the line.

   Bitmap images are resolution-dependent--if you scale them up or down in size, you are going to see losses in resolution.

   Vector images are resolution-independent--you can increase or decrease the size of an image without an appreciable degradation in quality.

   Some graphics programs draw in bitmap format, while others use vector. Some commonly used bitmap programs are Paint Shop Pro, Corel PhotoPaint and Adobe Photoshop. A bitmap program is what you would use for post-production work--touch-up and editing of a rendered image. Drawing in a bitmap program is much easier and more like using the natural media everyone is used to: pens, brushes, crayons, spray cans, etc.

   Vector programs include CorelDraw, Adobe Illustrator, Macromedia Freehand and the late MetaCreations’ Expression (recently acquired by a Hong Kong company and to be re-released under the name Creature House Expression. Adobe Photoshop, though a bitmap editor, has the ability to export files in vector (.ai) format. I don’t use Photoshop so I can’t say how effective this feature is; but posts to the list have stated it works well, so it’s definitely worth looking into. It is more of a challenge to master image creation in a vector program but they are powerful tools.

   RDS needs vector files for its cross-sections.

   The RD Manual lists a number of file formats which can be imported, including .cdr (CorelDraw), .ai (Adobe Illustrator) and .wmf (Windows metafile). It is generally held that RD is most successful with importing .ai files, so as a CorelDraw user I export my cross-section files in Illustrator (.ai) format.

   You may notice that your bitmap editor can optionally Save As… files in .wmf format--examples include Paint Shop Pro and Ulead PhotoImpact. But, be aware that this does not necessarily mean that you can create usable cross-sections in these programs. The format alone does not guarantee that the data contains vector information. So, even though the file is saved in a format that is listed as being compatible, the drawing may not be usable as a cross-section unless you have created it in a vector drawing program.

   Some of the following graphics programs are ones I have available and with which I am most comfortable; they are listed not because I think they are in all cases the best of their type, but just for information purposes. Others are programs which have been suggested by site visitors, or which I have run across but have not had time to test.

   You should download demo versions whenever they are available and make certain they meet your needs before registering or purchasing. Don't get fooled into thinking that just because a package is the most expensive in its category (think: Adobe) it is necessarily the best for your needs or will enhance your output. Familiarity, ease of use and skill count for a lot. As Chuck Yeager was always telling me as I went down in flames in that classic game: "Remember, it's not the machine...it's the man."

   A note of apology to Mac users: In most cases, I have not verified if the programs discussed are available in cross-platform versions.

   VECTOR PROGRAMS

   For a vector program I use CorelDraw (CD), and it is an excellent full-featured package. The full CorelDraw suite includes the vector drawing program, a bitmap editor, a raster to vector conversion program and several other useful utilities including a texture creator and font manager. The more I use and learn about this package, the more I am impressed with its capabilities and the more I like it. Its vast range of features and effects can be combined in an almost inexhaustible variety of combinations.

   Both the CorelDraw (vector) and Corel Photo-Paint (bitmap) programs are available as stand-alone packages. Be aware that Corel sells both the CorelDraw suite, and the CorelDraw program under the name CorelDraw. Be certain of what you're getting.

   In the past, Corel left older versions of its programs on the market at a reduced price long after upgrades were available. It appears that this may no longer be the case. When CorelDraw 8 was released, what was formerly known as CorelDraw 7 was marketed as CorelDraw Select. This package was not the complete suite; you should carefully check the specifications.

   If you can find any complete copies of previous versions, these would be an excellent value, better than any of the shareware vector packages available. The one disadvantage of some of the oldest versions is that they were written for Windows 3.1 and therefore use truncated file names—a real nuisance. It may be that CD5 onwards was Windows95; I recommend purchasing the most current version you can afford.

   If you can't locate an older version of CorelDraw, there are some very economical alternatives. MegaDraw Pro may be the closest thing to a Paint Shop Pro of vector packages--it combines ease of use, a full feature set and value. It is PC-only and includes many of the more commonly used features of the high-priced vector programs, including a full set of drawing tools and layers. It will export in .ai format (I have tested this function and it works perfectly). In addition, it has automatic star and gear patterns, and can create vector cel animations using a plugin which reduces file size by a factor of ten without loss of quality. $49 to register; Windows and NT only.

   At least equivalent, if not better, is Zoner Callisto. I haven't used it enough to comment extensively as to its function, but can say that it has a very professional looking interface with a full set of features. The program will export .wmf format files which I have found import without difficulty into RDS. A demo is available and you should give this program a try before making a final decision. The current release is v3, but I have been informed by the product manager that v4 is in development and that it will "probably" support .ai export. The downloadable version is $49 (the same as MegaDraw). There is a boxed version available, if that is your preference, at $69.

   There are other shareware vector drawing programs available, with a range of features and prices. There are even one or two freeware titles, but these latter offer no advantages over the drawing tools already available in RDS. I recommend searching some of the shareware repositories (ZDNet or CNet, etc.) and trying out a couple of these other packages before a final purchase. Whichever you choose, look for the ability to export in .ai or .wmf formats, layers (you can't imagine how useful these are), and a complete Help file (as they are shareware, you typically won't get any other documentation).

   BITMAP PROGRAMS

   My bitmap editor-of-choice is Paint Shop Pro (PSP) – one of the truly great values in graphics programs and one of the nicest and most helpful companies in the business. Somebody on the list described it as having 90% of the functionality of Photoshop, at 10% of the price. It’s shareware and also available in most better software stores. It supports layers, objects (vector-based graphic elements) and bezier transforms. However, as a bitmap editor, it cannot export its vector objects. It comes bundled with Animation Shop--an excellent animation utility. It typically lists at around $99, and even at that price you won’t find a better value in bitmap editors. I've seen it advertised with rebates at prices as low as $39.95, which would be an incredible bargain.

   Ulead PhotoImpact (UPI) is another fine bitmap editor. Up until the release of PSP5 (above), it had more features than Paint Shop Pro and it probably still does, particularly in the area of automated photo "styles" and color conversions. However, these are only useful if you plan to do a lot of retouching of photographs. It is more expensive than PSP and more difficult to learn to use. Like PSP, it has the ability to convert sections of an image into vector format for editing purposes but, again, these selections cannot be saved or exported in a vector format. Ulead makes a number of very fine utilities and this program enjoys wide support among skilled graphic artists, so you should definitely check it out.

   Corel Photo-Paint, part of the CorelDraw suite, is a powerful bitmap editor. It has features far beyond either PSP or UPI and is equivalent in most respects to Adobe Photoshop. The latter is held to be the professional standard but is, to say the very least, very expensive for what you get. For less than the price of Adobe Photoshop you can buy the entire CorelDraw suite.

   The bottom line: If you can afford the current CorelDraw suite, it is your best all-around value and will give you all the professional (whatever that means) tools you require. However, it has a significant learning curve and can be overwhelming. If you are new to computer graphics, want to be economical or appreciate a friendlier user interface and more comfortable learning curve, start with Paint Shop Pro for your bitmap editor and either MegaDraw or Zoner for your vector package. You can always move on to Corel or Adobe later. CLICK THE BOOK FOR SOME RECOMMENDED READING ON THESE PROGRAMS.

   II. CONVERTING BITMAP FILES TO VECTOR FORMAT

   If you create your cross-section in a bitmap program or acquire it from a scanner you will need to convert the bitmap file to a vector format. There are a few programs which can do this, saving you the trouble of manually tracing.

   CorelTrace is part of the CorelDraw graphics suite. When I used the version in CD4 I found it unsatisfactory—far too many extraneous nodes and multiple paths were created during the conversion process. The current version, now named OCR-Trace, is a considerable improvement the couple times I've tried it. Yet another argument for purchasing the CorelDraw suite.

   Adobe Streamline is a stand-alone application. This is a very good raster-to-vector conversion program and the one I use almost exclusively. Like all Adobe products it is expensive ($99-$125 is a little steep for a single-function program) and has a significant learning curve. I use only its basic features and perform other necessary steps in programs with which I'm more familiar. As with all trace programs, it is often necessary to edit out extraneous nodes. However, this program does an excellent job of matching the original paths and its thinning functions do a good job.

   There is a shareware program named ImpressionX. It may be the answer to finding a quality raster-to-vector conversion program at an economical price. It is capable of importing bitmap images and exporting either outlines or color-filled vector images in wmf format (Click for instructions). There is a save-disabled thirty day evaluation copy available (sounds like they're taking no chances), with separate Help files installed in the Programs folder. If anyone has used this program and can comment further, please do so and I will post your impressions here. The registration is a very reasonable $39.95.

   There is another shareware raster-to-vector conversion program named KVEC, available for only $25. It uses command-line syntax, i.e.: there is no Windows-standard interface. I have not taken the time to try it, so can make no comments regarding the program's performance. One user has emailed me and stated that the program is incapable of correctly tracing curved paths, producing a stepped path instead. I relayed this comment to the author, Karl-Heinz Kuhl, and he states that these results were due to incorrect settings. If you are comfortable with command-line syntax, for the price it's worth looking into. If you give it a try, please pass along your review and I will post it here. The author is interested in finding someone to design a W95 front-end. If you're into this sort of thing, he can be contacted through his web site at the KVEC link (above).

   Whichever program you use, you'll end up doing some manual thinning of extra nodes, welding together some adjacent nodes which have been traced as separate objects and adjusting Bezier handles before the cross-section is completely usable. I do all that in CorelDraw because the layers function allows the superimposition of the original and traced images.
   
   III. GETTING THE CROSS-SECTION INTO RDS

   Once you've created the cross-section, the remaining steps are straight-forward:

   Start RDS.

   1. Click on Create Empty Scene.
      
   2. When the Perspective Window appears, click-and-drag the Free-Form icon into the Perspective Window. The Modeling Window will appear.
      
   3. In the Modeling Window, use the Selection Tool to click on the Drawing Plane (if it’s not highlighted—i.e.: green) to make it active.
      
   4. Click on File/Import. When the Open dialog appears, double-click on the cross-section (.ai) file previously created.
      

      The image created will be imported to the Drawing Plane as the first cross-section.
      

   5. Click on View/No Preview. This helps to visualize the Sweep Path more clearly.
      
   6. Click on the Left wall of the Modeling Box—the one with the pink Sweep Path. Zoom in if you need to see the sweep path more clearly.
      
   7. Click on the pink Sweep Path at any point, and two small white squares will appear at both ends.
      
   8. Shift-click and hold on the small white square on the right and drag it to the left or right, until the Sweep Path is the same length as the desired thickness of your object. (Shift-click constrains the movement of the control point to 45 degree increments.)
      
   9. Click on any of the Preview Modes, and you should see your finished object.
      

      IV. SWEEP PATHS AND SCALING ENVELOPES

      The manual tells you that you can also import sweep paths and scaling envelopes. This is true, up to a point.

      Simple sweep paths are imported relatively easily. But, importing scaling envelopes--which at first sounds like the answer to a lot of modeling problems--turns out to be an almost useless function.

      The reason for this is that any envelope created in another program is always imported symmetrical in all planes. There is no way around this. So, about the only thing this feature appears to be good for is simple lathed objects. (If I'm wrong about this, I'd certainly like to know.)

      have fun
      

      
      
      
      

      All constructive comments, suggestions, and corrections are welcomed.

      All contents copyright 1998-2000 bilagaana. All rights reserved. The images may not be copied in any form without the permission of the author. Digitally watermarked.