What is the cross section 2-D shape made at the cut?

Answer 1

We are missing information here. We need to know what shape you are working with so that we can tell you what shape is made at the cut.

Example, if you took a cylinder, and made a cut down the middle the shape left is a CIRCLE. If the cut is made at an angle, you get an OVAL, if the cut is made lengthwise, you get a RECTANGLE.

Answer 2

This is research in progress to develop graphic interface that might serve the community studying processes and models in three dimensions in a comparable way to the role that the GMT software (Wessel and Smith, 1991) played in representation of two dimensional maps and other geophysical parameters. At a recent NSF-sponsored Earthscope workshop in Snowbird, Utah, there were several statements made with respect to the need for a software appropriate for representation of models, their cross-sections and other projections. It is recognized that particularly for 3-D studies, proper visualization of models is essential. We are trying to respond to this need, in part using the experience accumulated during the 25 years of seismic tomography at Harvard (Dziewonski, 1975; Dziewonski et al., 1977), even though it did not make much of an impact at first, since the color graphics did not exist yet. The first tomographic papers using color maps and cross-sections (Dziewonski, 1985; Woodhouse and Dziewonski, 1984) made their impact felt. In further studies we have used 3-D cut-ins (Dziewonski and Woodhouse, 1997), and 3-D iso-surface representations (Su et al., 1994). This proposal request support for trying to bring together in an interactive package the existing and new tools for visualization of 3-D models. Since most of our work has been focused on global problems, the illustrations presented here will exemplify this aspect of our graphics. However, incorporating changes that would be needed to include also the regional mapping capabilities should not be difficult. We believe that its funding is within the objectives of support for the pre-Earth scope activities.

Active participants in this project are Adam M. Dziewonski, Göran Ekström, and Wei-jia Su.



Proposed Work
The concept of the Geomap software package is a user friendly plotting program specifically designed for use in the geoscience community. The design of this program is focused on the ease of use, interactive execution, `what-you-see-is-what-you-get' principle, and requirement of the least amount of learning. The user menu, tab choices, check boxes and pop-up dialog boxes are intended to be intuitive, and will keep reading of the user's manual to a minimum. The current program is written in C++ on the PC platform. The user interface part of the code is written in Microsoft Visual C++, which provides a very good development environment. The major portion of the code, however, is machine independent. With some effort, it surely can be ported to the Unix or Linux system. The memory and disk space usage are kept to minimum. An early version of this program has been used by geoscientists at Harvard University for more than a decade. It allows generation of many types of maps and graphs. We would like to develop this program further and make it available to geoscience community at large. The intended main functions of the program are:

1. Global mapping:

plot grids, coastlines, plate boundaries
plot symbols of different shape, size, color
plot texts
plot vectors
plot symbols of different shape, size, color
plot models (2D contours, cross-sections, cut-ins or 3-D iso-surfaces
plot image data (topography, geoid, etc.)
2. Regional mapping :

plot grids, coastlines, plate boundaries
plot symbols of different shape, size, color
plot texts
plot vectors
plot symbols of different shape, size, color
plot models (2D contours, cross-sections, cut-ins or 3-D iso-surfaces
plot image data (topography, geoid, etc.)
3. Projections:

Mercator
Aitoff
Hemispheric projection
Equidistant cylindrical
Additional projections can be implemented as needed
4. Earth models:

3-D spherical harmonic plus Chebyshev, Legendre polynomials or B-splines for radial functions
B-spline 3-D models
spherical harmonic maps
Block models
Grid models; Geomap can plot any pre-calculated grid model; this allows user plot model obtained using an arbitrary parameterization.
Global models can be plotted within the stated latitude and longitude limits
5. Symbols:

Fixed size symbols
Variable size symbols
Automatic scaling of symbols
Capability to plot symbols on a cross-section
Vectors
In addition, the program has these features:

3-D cut-ins allow the user to view an Earth model in a 3-D perspective on several (usually three) planes. The advantage of this kind of visualization is that no distortion of any sort is applied. Several parts of the Earth's mantle velocity (or other properties) can be seen at the same time.
Cross-sections can be made along the entire great circle or within the specified limits, using either spherical or Cartesian geometry.
3-D iso-surface plots go beyond the traditional visualization through maps or slices. A more direct view of the Earth's interior is made available through three-dimensional visualization. This method is becoming more and more popular with the development of different commercial or non-commercial software packages. An algorithm of ray-casting has been used to shade the iso-surfaces. Perspective projection has been used so that the Earth model appears more natural. The program is able to plot the earth model in in either spherical or Cartesian coordinates.
Interactive resizing of plots. Multiple maps can be plotted on one page. Each can be individually resized and moved even after all the elements and models are already plotted.
Interactive definition of color tables. The color table can be interactively defined and saved for later use. The user has option to use predefined color tables.
Interactive incorporation of text; define text font, size, color, click-drag to move text, click to delete etc.
m Interactively change line width, color, line type, fill color for any plot element and replot in seconds.
Print to postscript.
Examples
We shall present here several examples of the application of Geomap to plotting Earth models.
Figure 1 is a screen-dump of the interactive display; post-script files have significantly better resolution. Here, shear velocity maps from model S12 (Su et al., 1994) and Grant (1997) are compared at a depth of 100 km. Notice the menu choices on the right; many of the available choices are hidden, but can be displayed and implemented by pointing at the tab.