This article describes a process that produces computer-generated isometric guides directly from a scan of an engineering drawing. The following is a step-by-step description that will produce a product illustration directly on the computer from paper engineering drawings. Compared to traditional methods, it reduces the cost of an illustration by approximately twenty-five percent and can provide a further cost advantage due to the extraordinary increase in throughput. Our volume has more than doubled since we implemented this process.
Step 1: Scanning
Scan the engineering drawing using a resolution suitable to its size and complexity. Scan into three pieces, "Front," "Side," and "Top." After scanning the engineering drawing, erase extraneous items such as call outs, title blocks, dimensions, etc.
Step 2: Auto-Trace
Auto-trace programs, which convert scanned raster images to vector graphic files, need their settings modified to produce acceptable results. To do this, open Corel Trace, select the batch tool, select your scans, select Trace - Edit Options -choose the Lines Tab and use the following settings:
* Curve precision - Very Good
* Line Precision - Very Good
* Target Curve Length - Medium
* Sample Rate - Fine
* Minimum Object Size - 5 pixels
* Outline Filter - None
* Max Line Width - 16 pixels
* Create lines of uniform width - 1 pixel
* Check - Horizontal and Vertical line recognition
* Check your File - Save Options - Save Options Directory - Change the Default Directory to the directory where you want the vector graphic (*.eps) files saved.
* Now launch the Auto-trace function by clicking on - Trace All
* Close the program when Corel Trace is finished.
Step 3: Create a Master Isometric Ellipse
To create a master ellipse, open CorelDRAW to a new drawing, select the ellipse tool (circle in the Toolbox) and while holding down the Control Key create a perfect circle. Then use the transform tool to apply a vertical scale of 57.4 percent. Using the Transform Roll-up, rotate the ellipse 120 degrees and Apply to Duplicate twice. You will now have a "top," "front," and "side" ellipse. Save the result as Ellipse.cdr and keep that as a master. Select all three ellipses and copy them to the clipboard.
Step 4: Create Layers
Start a new drawing and paste the ellipses you just created onto the drawing. Reduce them to 25% of their original size and place them outside the paper border. In order to differentiate between the auto traces when they are imported into CorelDraw, they need to be color-coded. Open the Layers Roll-up and create the following three new layers with the stated names and settings:
* Front - Select Visible, Deselect Printable, Deselect Locked, Select Color Override and choose Red.
* Side - Select Visible, Deselect Printable, Deselect Locked, Select Color Override and choose Blue.
* Top - Select Visible, Deselect Printable, Deselect Locked, Select Color Override and choose Green.
Printable was deselected so that when Print Preview is invoked the Auto Traces will be invisible. Locked was deselected so that the auto traces can be moved.
Step 5: Import
Import the Auto-Traces onto their respective layers correcting any orientation and rotation as necessary. Save the drawing.
Step 6: Create the Front
From the Layers Roll-up, deselect MultiLayer and select the "Front" layer. Select the trace and from the Transform Roll-up, choose a 86.6 horizontal scale and apply, then a -30.0 degree vertical skew and apply. The result will be the guide for the left face of the illustration.
Step 7: Create the Side
From the Layers Roll-up, select the "Side" layer. Select the trace and from the Transform Roll-up, choose a 86.6 horizontal scale and apply, then a 30.0 degree vertical skew and apply. The right side guide is now complete.
Step 8: Create the Top
From the Layers Roll-up, select the "Top" layer. Select the trace and from the Transform Roll-up, perform a vertical scale of 86.6% to your trace and apply. Choose a -30.0 degree horizontal skew and apply, then choose rotate -30.0 degrees and apply. You now have a "plan view" guide in isometric. Next, choose each layer and position them so that everything lines up at the front, right, top corner.
Step 9: Setting Preferences
In order to control how the software produces vector objects, some of CorelDRAW’s default settings need to be changed. Choose Preferences (Ctrl + J) and set the following:
* Place Duplicates and Clones - Horizontal = 0.000, Vertical = 0.000. These settings will ensure that duplicated objects are not offset.
* Nudge = 0.010. The default nudge is too large for technical work. Using this setting gives you more control of your work. A thin sheet metal thickness can be shown with two or three nudges.
* Constrain angle = 15.0 degrees. This is the Corel default and is perfect for an isometric projection.
* Miter limit = 45.0 degrees. This is the Corel default.
* Undo levels = 4. Limiting undo levels will conserve system resources.
Step 10: Constraining lines on an isometric axis
Make Layer 1 active. Choose your pencil tool (straight line) and while holding down the control key on the keyboard draw a line. While still holding down the key, watch the status line while moving the end point in a good sized circle you will note that the line jumps in 15 degree increments. Since the normal axis in isometric is 30 degrees, this will provide all "On Axis" and most of the "Off Axis" conditions you will encounter. Releasing the control key permits drawing on any angle.
Now the magic can happen. If you combine the ellipses, constrain the angles, and use the Auto-Traces you have everything you need to complete an illustration. I usually require approximately ten minutes to complete the above and begin drawing. In this time conventional methods would be less than twenty percent complete.
In a time of restricted budgets and impossible deadlines a process like this can be an invaluable tool. Our per-person output is a multiple of the organizations we compete with who use "high tech" methods to produce their isometrics. In the technical illustrating field this may be as close to "good, fast, and cheap" as we are likely to get.
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