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solidify/README: some documentation
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Werner Almesberger
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solidify/README
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solidify/README
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solidify - Merge two opposing faces of a part into a solid
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==========================================================
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Solidify is a tool for adjusting the orientation of two opposing faces
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(surfaces) of a three-dimensional part such that they correctly align
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with each other, and to generate output that represents the volume
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(solid) enclosed between the two faces.
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Theory of operation
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-------------------
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The shape of a three-dimensional part can be reconstructed by scanning
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two opposing faces of the part. The part is then the space between the
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two faces.
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When doing this in practice, a few problems arise. One of them is that
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the faces will not be perfectly opposed. E.g., the part being scanned
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may be inclined, rotated, or shifted. Solidify implements the following
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operations:
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- change the inclination of the part along the x and y axis (i.e., the
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part's z plane is tilted). The general assumption is that the part is
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scanned with its main surfaces parallel to the z plane and that only
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small adjustments are necessary.
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- change the part's height above the z plane. There is a conceptual z0
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plane, parallel to the z plane, that is coplanar with a reference
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surface in the face. The height of the z0 plane above the z plane
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can be adjusted.
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- set the distance between the z0 plane of the top face and the z0 plane
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of the bottom face. This defines the thickness at some point of the
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part.
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- align the two faces by rotating them around the z axis and by shifting
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them in the x and y direction.
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Except for setting the distance between z0 planes, all these operations
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are interactive. Solidify furthermore provides visual clues that help to
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minimize anomalies.
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Solidify reads faces as comma-separated point clouds generated by
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Dr.Picza3. It outputs a set of files that define the part in POV-Ray.
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Starting a project
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------------------
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For a project, the following information is necessary:
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- the name of the project file. This file must not yet exist. Solidify
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store information pertaining to the project, such as the names of the
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file containing the faces and the orientation set for the faces.
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Solidify project files typically have the extension .sfy.
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- two text files containing the two faces a comma-separated point
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clouds. If a file name ends with the extension .bz2, solidify will
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uncompress the file on the fly with bunzip2.
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If instead of a file name a HTTP or HTTPS URL is given, solidify will
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try to download the file with "wget" into a directory called .cache.
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This directory must be manually created for this purpose. On further
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invocations, solidify will load the file directly from the cache.
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- the distance between the z0 planes of the two faces. Typically, this
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is the thickness of the part in some area that is flat on both sides.
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The distance is measured in millimeters.
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To generate a project name.sfy with the faces top.svn and bottom.sfy
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and a z0 distance of 1.5 mm, run
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$ solidify name.sfy top.csv bottom.csv 1.5
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Solidify will load the faces (this can take a while) and then show the
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top face for z0 plane editing.
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Leaving solidify
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----------------
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To exit solidify and save the current settings in the project file,
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simply press "q". To quit without saving, terminate solidify by pressing
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^C in the shell.
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Changing an existing project
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----------------------------
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Start solidify with the name of the project file, e.g.,
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$ solidify name.sfy
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Solidify will load the face files and then show the top face for z0
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plane editing.
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Adjusting the z0 plane
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----------------------
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There are four buttons at the right side of the screen. The ones labeled
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"A" and "B" are for editing the top and bottom faces.
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Note that each face has its own z0 plane, which is controlled
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independently from the of the other z0 plane.
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Display
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- - - -
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The center area of the screen shows the respective face from the top.
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Areas below the z0 plane are shown in red, areas above the z0 plane are
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in green. Intersections of the z0 plane with the face are shown in blue.
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The intensity of the color increases with the distance between the face
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and the z0 plane. To make it easier to see which way the planes are
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facing, areas with only a small difference and thus often directly
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adjacent to an intersection (blue) are colored with more intense red and
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green.
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Below and on the right side of the central view, lateral projections of
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cuts at the cursor position are shown.
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Control
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- - - -
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The z0 plane is manipulated with the mouse wheel. Rotating the mouse
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wheel with the pointer near the center of the main view raises or lowers
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the z0 plane. Outside the center, rotating the mouse wheel tilts the z0
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plane by pushing or pulling at the pointer position.
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The center area is marked with a yellow circle that becomes visible when
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approaching it with the mouse pointer.
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Workflow
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- - - -
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There are two objectives when adjusting the z0 plane:
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- it should intersect the face at the point(s) that define the distance
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between z0 planes, and
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- the z0 plane should be parallel to the principal orientation of the
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part
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As a first step, it's usually best to pick one or two flat reference
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areas containing the zones where the distance was measures, and to tilt
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the z0 plane until it is roughly parallel to these areas. This can be
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easily seen on the lateral projections.
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Then the z0 plane is be raised or lowered until it intersects. The
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result should be a large blue field that covers the reference areas.
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If the part is not only tilted but also warped, it may not be possible
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to evenly level it. For achieving as good an adjustment as possible, one
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should attempt to maximize and evenly distribute the blue areas on the
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main view.
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Aligning the faces
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------------------
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When clicking the "A+B" or "B+A" button, both faces are shown
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superimposed, with the bottom face rotated around the y axis.
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With "A+B", the top face is manipulated, with "B+A" the bottom face.
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The display is the same in both cases.
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Display
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- - - -
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The following colors are used:
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- white: both faces overlap
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- green: only the top face. There are no points in the bottom face at
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this location
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- green: only the bottom face
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- blue: the top face is below the bottom face
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Control
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- - - -
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Again, the faces are controlled with the mouse wheel and the function of
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the wheel depends on whether the pointer is in the central area or not.
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The central area is marked with a yellow circle that is displayed when
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the mouse pointer approaches it.
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To rotate the face around its center, move the mouse pointer outside the
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center area and spin the mouse wheel. The larger the distance from the
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center, the faster the face spins.
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Spinning the mouse wheel when the pointer is inside the central area
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shifts the face along the x and y axis. (*) The central circle is
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divided into four areas: in the left and right area, the face is shifted
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horizontally, in the upper and lower area, the face is shifted
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vertically.
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(*) When shifting the bottom face, the direction depend on the face's
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rotation. This is a bug but it has no other ill consequences.
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Workflow
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- - - -
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The faces usually don't overlap perfectly. The goal is thus to
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distribute the red or green overlaps evenly.
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If significant portions of the part are drawn in blue, this means that
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the orientation or the height of the z0 planes is not correct.
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If the part is very thin, it may be necessary to raise the faces a but
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above the z0 plane to keep the faces from intersecting due to warping.
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Rendering with POV-Ray
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----------------------
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When invoked with the option -p, solidify generates the following three
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files:
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- name.inc: a POV-Ray file that renders the part. The part is called
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"Part_name"
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- name-top.pgm: a PGM (Portable GrayMap) image containing a height field
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for the top face
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- name-bot.pgm: height field of the bottom face
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Invocation is as follows:
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$ solidify -p name.sfy
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A part can be used in a POV-Ray scene by #including its name.inc file
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and then placing the object.
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