Author Topic: Scaling (?) problem  (Read 821 times)


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Re: Scaling (?) problem
« Reply #15 on: April 21, 2018, 03:14:44 PM »

This secret I just discovered yesterday is dipped in dark chocolate:

For me, working in Paper Space mode with view windows is a painful experience because of the constant redraws and other little nonsense.

Likewise, working with bitmaps in model space is a pain because the bitmap is always regenerating and hiding stuff.

Eg, for 2D and 3D elevations and sections I usually save images of the model, then load the images into model space and add notes, arrows and dimensions.

However, if I load bitmaps directly into paper space (with no view windows) it is surprisingly pleasant to work since the bitmaps don't seem to have to ever redraw. They remain stable. As I add more of the other entity types I will begin to feel the redraw delay but it will probably never get as bad as with view windows. Plus, pressing esc to halt the delay always seem to work.


« Last Edit: April 21, 2018, 03:16:54 PM by Lar »


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Re: Scaling (?) problem
« Reply #16 on: April 21, 2018, 09:17:14 PM »
Here is a 3D mode "secret" that I learned the hard way.

When generating images the program divides the image depth by some (unknown) number of sections perpendicular to the line of sight from the viewer to the "View Center" along the viewing Z axis (it does this because it can't work with an infinite number of distances).

Then it uses the "Z slices" to determine which objects are nearer the View Point (camera) and which are farther away, by figuring out which Z axis slice(s) the object is in. Then it generates the image so closer objects are displayed on top of more distant objects.

The depth of each slice is proportional to the view distance and not to the drawing depth. In most cases this is OK. But as the viewing distance increases the effective depth of each Z slice increases - or to put it another way, the ability of the program to distinguish distances between close objects and determine which objects are nearer and which are farther is reduced. At some view distance the program will consider close objects to be at the same view distance.

So why should you care? Suppose you have two different colored surfaces (planes or grids) that are very close together. With a short View Distance the program renders them correctly, with the closer surface displayed in front of the more distant surface. But with increasing View Distance a point will be reached where the program tries to display both surfaces at the same distance. When this happens surface planes will be displayed in the colors of both surfaces in a kaleidoscope pattern.

The facets.jpg image shows what happens when you have multiple congruent surfaces - three copies of the same surface, in three colors, at exactly the same place. The program has problems deciding which color to use, so it uses all three. Parts of each facet is displayed in red, green and cyan. Again, this is what happens at close view distances when multiple surfaces actually exist at the same place.

Now look at the "fwd smoke pipe" image. Initially I created the gray smoke pipe and then created the red and black parts of the "E" as surfaces a slight distance above the gray surface - in effect "painting" the "E" over the gray surface. At short View Distance this worked perfectly. But as I increased View Distance to see the entire ship the "E" partially or completely disappeared behind the gray surface. Usually the "E" would become alternating red and gray and black and gray streaks.

The "hull" image shows the helo deck landing pattern (white and red) that was "painted" over the dark gray deck. Also, the "5" was "painted" over the hull surface. Again, at close View Distances it displayed correctly, but when I backed out to view the entire ship part of all of the patterns disappeared behind the gray deck and hull.

I tried increasing the distance between the "paint" and the underlying surfaces, but as the View Distance increased at some point the "paint" would partially disappear. This is because the Z slice thicknesses eventually became greater than the distance between the "paint" and the underlying surface. The resulting display colors were mixed looked pretty much like the "facets" image. Worse still, if the distance between the "paint" surfaces and the underlying surface gets larger, shadows start appearing under the "paint" in close-up views, so no view is usable!

The solution?

1. Draw the outline of the "paint" surfaces and extrude it perpendicular to the underlying surface.

2. Find the Surface Intersection of the extruded line and the underlying surface.

3. Explode the grid surfaces into individual planes.

4. Where "paint" and background overlap, redraw each individual grid facet as polygons, with individual polygon pieces for each "paint" surface color and the background surface color. This splits each grid facet into background and "paint" colors. Be sure to delete the original background facet!

5. After all facets have been redrawn, select all facets in the surface and combine them with "Solid Define." This causes the surface to display as a smooth surface. If you just grouped all the pieces each facet would display as a flat surface and the overall surface would not display smoothly.

Now there is only one surface at each "paint" or background point. Without the overlapping surfaces of different colors the painted surface will display correctly at all View Distances. It can be a lot of work, but it is the only way to get the desired result. *

The "fwd smoke pipe" drawing was created in this manner, and the "E"displays correctly at all viewing distances.


NOTE: Well, maybe not the only way. You can always generate the desired paint and background color image in a program like Photoshop and save it as an image file (JPEG, PNG, etc.) Then you can try to apply the image to the surface as a Texture Map. Good luck! Texture maps are rotated, stretched and warped to fit over curved surfaces and they can be very difficult to control. But it is possible with a lot of work and even better luck!
« Last Edit: April 21, 2018, 09:28:02 PM by Dr PR »
DesignCAD user since 1987