Version Compare: A simple polygon example

The Autodesk Design Review 2008: DWF Version Compare article provides an overview of how the new Version Compare feature works. The Version Compare: A simple polyline example article provides a simple example of how comparisons for polylines work. This article takes the same approach for polylines but does so for polygons.

For the polyline article I:

1. Created a DWG file with 9 polylines.
2. Published a DWF file containing the 9 polylines.
3. Converted the DWF file to ASCII and saved it as the original DWF file.
4. Made a copy of the ASCII DWF file, edited it with a Text Editor, and saved the copy as the modified DWF file.
5. Compared the original DWF file to the modified DWF file and reported the results.

The purpose of the polyline test was to determine if tiny changes, with all other things being exactly equal, would be detected by the Version Compare feature. Except for color, a known limitation, they were. For this article, the purpose is to demonstrate how changes in AutoCAD affect Version Compare results in the published DWF files. An AutoCAD polygon is the geometric primitive being tested.

For the polygon case covered by this article, the approach is the basically the same as the polyline case with a few twists to make cover other aspects of Version Compare. So I:

1. Created a DWG file with 11 polygons and saved it as dwf_compare_polygons1.dwg.
2. Published a DWF file containing the 11 polygons as dwf_compare_polygon1-Layout1.dwf.
   
3. Made a copy of dwf_compare_polygons1.dwg and saved it as dwf_compare_polygons2.dwg.
4. Edited dwf_compare_polygons2.dwg to make the desired changes to 10 of the polygons - leaving one untouched.
5. Published a DWF file containing the 11 polygons as dwf_compare_polygon2-Layout1.dwf.
   
6. Combined dwf_compare_polygon1-Layout1.dwf and dwf_compare_polygon2-Layout1.dwf, renamed the sheets to revision1 and revision2, and saved the new DWF file as dwf_compare_polygon1.dwf.
7. Used the compare dialog Options button
   
   
   
   to specify red for Additions and blue for Deletions. By default, just like what Autodesk Architecture does for DWG comparisons, Additions are green and deletions are red. I wanted to highlight the additions, so I selected red for my Additions color. In deference to those who are red/green color blind, I selected blue for my Deletions color.
8. Compared the revision1 sheet to revision2 sheet using just the one DWF file. Now the first sheet contained the markups.
9. Inserted the unmarked up original sheet from dwf_compare_polygon1-Layout1.dwf.
10. Reordered and renamed the sheets to have revision1, revision2, and revision1 with markups.

The net effect of these steps is that unlike the polyline article where I compared two different DWF files, I compared two sheets in the same DWF file. This worked. I feared I might get some kind of sharing violation, since the DWF file was already open, but it was allowed. After renaming the sheets, I was left with one DWF file that contained three sheets: the first revision, the second revision, and the first revision with the markups generated by the Version Compare of the first two sheets.

Download dwf_compare_polygons.dwf (117.3K)

Now let's talk about the changes between the sheets:

• No difference - This is the control group or baseline.
• Vertex added - The 5 point polygon changed to a 6 point polygon by using grip edit to insert an additional vertex.
• Vertex deleted - The 5 point polygon changed to a 4 point polygon by using grip edit to make one vertex coincident with another.
• Vertex changed - The point at the apex of the polygon was lowered by using grip edit.
• Edge color - The polygon was placed on a layer whose color was green.
• Edge pattern - The polygon was placed on a layer whose line pattern was dashed space. This also required setting of a line type scale which was applied to both the original and modified DWG files. In addition, I added a small line near the polygon, so it was easy to see that the pattern for the layer had indeed been applied.
• Edge weight - The polygon was moved to a layer whose line weight was noticeably thicker.
• Face color - A SOLID hatch of green was applied to a polygon. A SOLID hatch of magenta had been applied to all of the polygons in the original DWG.
• Hatch - The hatch was modified from ANSI31 to GRASS.
• Gradient - The gradient pattern was modified from a circular pattern to one oriented about a center line.
• Region - In the original, a region was formed using one of the polygons and a circle. A CORK hatch pattern was applied. For the modified DWG file, a HONEY pattern was applied.

Upon comparing the two sheets in the same DWF file:

The results were basically as expected:

• No difference - This shows an unexpected difference. Software developer, Neil Wan, analyzed my sheets to determine that the polygon in question actually consists of one triangle and three trapezoids. There are small differences in some of this geometry (highlighted in red):

  In revision1:    T 3 2147157453,286666        2147156735,286144        2147158171,286144    T 4 2147155874,285519        2147159032,285519        2147156735,286144        2147158171,286144    T 4 2147155155,284997        2147159751,284997        2147155874,285519        2147159032,285519    T 4 2147127624,264994        2147187282,264994        2147155155,284997        2147159751,284997

  In revision2:    T 3 2147157453,286666        2147156735,286144        2147158171,286144    T 4 2147154821,284754        2147160085,284754        2147156735,286144        2147158171,286144    T 4 2147139027,273279        2147175879,273279        2147154821,284754        2147160085,284754    T 4 2147127624,264994        2147187282,264994        2147139027,273279        2147175879,273279

  This is an artifact of the publishing process. Version Compare is very precise in this regard.
• Vertex added - The deformed area based on the additional vertex is highlighted as an addition (red).
• Vertex deleted - The area removed by deleting the vertex is highlighted as a deletion (blue).
• Vertex changed - By lowering the top vertex point, the original area is shown as deleted (blue) and the resulting area is shown as added (red).
• Edge color - The edge color change from black to green is not detected. This will be included in a future release.
• Edge pattern - The original solid edge appears as a deletion (blue). The dashed edge as well as the extra line appear as additions (red).
• Edge weight - The wider edge appears as an addition (red). Through obscured by the wider red edge, the original edge appears as a deletion (blue). The blue edge can be brought to the forefront by selection the Deletions markup item.
• Face color - The face color change from magenta to green is not detected. This will be part of a future release.
• Hatch - The geometry from the ANSI31 pattern appears as a deletion (blue). The geometry for the GRASS pattern appears as an addition (red). As these patterns are sparse, the red and blue appear to mix in the polygon.
• Gradient - The mixture of original and new gradient pattern occurs much like what happens for hatch.
• Region - The hatch and gradient comparison for polygons apply equally to regions.

My work with polygons today reminds me of a line from a Todd Rundgren song called " Born to Synthesize":

Pyramids, spheres, and obelisks are the patterns of all creation
But the red polygon's only desire is to get to the blue triangle

Red is the lowest color in the spectrum. Blue is higher. A triangle is the most stable 2D polygonal shape. In short, the polygon wants to better itself. Now on what other CAD blog will you get rock 'n' roll trivia like that?

The Version Compare feature errs on the side of caution. It is better to identify a piece of geometry as changed, although it may not really have, instead of ignore a piece of geometry that really has changed. This should be taken into consideration when using the feature. Version Compare can't determine if the polygon has made it from red to blue, but it sure can tell when geometry becomes a triangle.

Comments

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