OOF: Finite Element Analysis of Microstructures
To avoid complications later, we'll define a few terms here.
The ppm format micrograph that was loaded into ppm2oof, or modified versions of it. Sometimes we also use "image" to mean whatever's displayed on the right hand side of the graphics window.
One of the fundamental picture elements of the image. Because the image may be magnified or shrunk on the screen, a pixel is not necessarily drawn using only one screen pixel.
- Screen Pixel
The smallest dot that can be displayed on your screen. We won't usually need to refer to screen pixels--most of the pixels we refer to are the pixels of the ppm image.
- Material Image
The image with the colors replaced by the colors of the materials which have been assigned to each pixel.
- Current Selection
Much of using ppm2oof consists of selecting some pixels and doing something with them. The set of selected pixels is the current selection. The set can be set with the Select dashboard or the /select menu.
One of the triangles of the mesh.
One of the elements of the mesh.
- Coordinate System
ppm2oof expresses almost all lengths in units of the edge length of a pixel in the image, and all areas in units of a pixel area. As usual, the x axis is horizontal and the y axis is vertical. The origin is at the lower left corner of the image. Pixel coordinates are integers, but the coordinates of mesh points are floating point numbers. Pixel (i,j) covers the region i < x < i+1 and j < y < j+1. Because ppm2oof is written in C++, not Fortran, the bottom row of pixels is row 0, not row 1. In mesh coordinates, an image n pixels wide goes from x=0.0 to x=n.
The only lengths that are not expressed in pixel units are the positions of the nodes of the mesh, when written out to the goof file. The positions are converted to physical units using the /width variable.
- goof file
Grid for OOF: ppm2oof's output file and oof's input file, containing the finite element mesh. By convention, this file has a .goof suffix.