TOMOPLOT User's Guide

Version 1.0

by
Kent S. Roessler

Department of Interior
U.S. Bureau of Mines
Twin Cities Research Center

May, 1991

Introduction

This file summarizes tomographic plotting/analysis package called TOMOPLOT, which was developed by the author in the Rock Mass Behavior/Geotechnology Division of the U.S. Bureau of Mines, Twin Cities Research Center. The primary function of this software is to contour, shade, and locate zonal changes (i.e., permeability, voids, etc.) in tomographic images.

Tomoplot was written exclusively in the C programming language and only runs on IBM-compatible machines. Other requirements include: math co-processor, EGA or VGA graphics adapter, and a mouse (optional).

To select a printer, enter SETUP. To run the contouring program, enter TOMOPLOT. You should get the introductory menu on the screen. Press the carriage return and you will see an option menu to execute Continue, General Information, or Quit. Select Continue to get to the TOMOPLOT main menu.

1. Data file format

Data files for TOMOPLOT are generated by BOMCRATR as a part of the *.SUM file.

TOMOPLOT can read the *.SUM file directly. Examples are included in this distribution diskette. Data files can also be generated by any suitable editor, spreadsheet, word-processor, or in-house software that sets up the file in the correct format and is saves it as an ascii text file.

A data file consists of comments (beginning with a // and located at the top), an @ symbol separating the comment section from the rest of the data file, x- range and y-range values, header, x-axis label, y-axis label, number of rows to skip from the top and the bottom, number of rows (including skipped rows) and columns of velocity data, and finally the velocity data itself. The two x-range values and the two y-range values must be in increasing order. If y is specified in terms of depth, negative values must be entered so the second value (top of grid) has a greater value than the first y. The option of skipping rows at the top and bottom is provided because extra rows are sometimes used at the top and bottom of the grid when performing curved ray tomography. The velocity data is in the form of a matrix with the top of the grid at the top of the matrix.

2. Contouring and shading an image

To contour and shade your data file, select option 1 from the TOMOPLOT main menu. A sub-menu will pop-up and allow you to assign a color for each velocity contour value. The contours range from the lowest velocity to the highest velocity and each of them must have a unique color. There are 13 colors to choose from, and each color can only be used at most once. You also have the option of choosing the default colors by selecting ESC. The default values use light colors for low velocity zones and the colors get darker for the higher velocity zones. There is a help screen that can be accessed at anytime by selecting F1. All user inputs are error-checked and if something is invalid, a message will pop-up indicating the problem. If you selected manual input, then press F2 when finished, to save the contour color values.

Following the assignment of contour colors, a pop-up window appears querying the user for the data file to use. If you select a file that doesn't exist or is incorrectly formatted, you will get an error message and be able to try again.

After loading in a data file, another sub-menu pops up allowing the user flexibility in the contour values to plot. A window at the top indicates the minimum and maximum contour values or range that the user can select from. A small window in the middle of the screen asks you how many contour values to plot. The value must be > 1 and < 10. If the value is invalid an error message will pop-up and you will be allowed to try again. Next, the contour values must be specified up to the number you indicated, All values are error checked and must be in the valid range and in increasing order. When finished, select F2 to save and continue. You can also select ESC and use the default values which range from the minimum to the maximum and are equally spaced. A help screen can be accessed at anytime by selecting F1.

Upon completion of the previous sub-menu, the contour (shaded and unshaded) plots are drawn along with a legend showing the velocity ranges and their representative colors, and another menu. This menu allows you to expand the unshaded contour, expand the shaded contour, print, change contour values, plot a new file, or quit.

3. Creating a difference file

To create a difference file between a sequence of images, select option 2 from the TOMOPLOT main menu. A small window will appear asking for the first data file (the file to subtract). Then another window appears asking for the second data file (the file to subtract from). These queries are also error checked. Once the files are loaded, another window pops up and queries the user for the difference file to create. Once the difference file is created, control goes back to the main menu.

4. Locating zone changes in the difference image

To locate regions of maximum change in the difference image, select option 3 from the TOMOPLOT main menu. A small window pops up and queries the user for the data file to open. After the data file is loaded two windows appear on the screen. The one at the top of the screen shows the minimum and maximum velocities of the data file. The one in the middle asks for the pixel velocity increment or histogram bar width. This is needed to display a cumulative histogram of the frequency of occurrence of the velocity pixels to calculate the threshold that separates the zones (i.e., fractures, permeable layers) from the background. Choose an increment such that you get a bimodal histogram that separates the zones of interest from the background. After this value is entered, a histogram is plotted showing the calculated threshold. If the threshold or the histogram bar width does not give meaningful results, you can keep changing them until you obtain a suitable bimodal histogram and threshold.

After obtaining a desirable threshold, the velocity pixels that are greater than the threshold are plotted and the orientation of the zones are shown.