Grid Math

Use the Grid and Image > Grid Math menu option (geogxnet.dll(Geosoft.GX.MathExpressionBuilder.MathExpressionBuilder;RunGrid)*) to create, save, load and execute math expressions for your grid data. This easy-to-use standardized dialog provides all the math expression options on a single tabbed dialog.

Grid Math dialog options

Step 1: Enter a mathematical expression, alternatively build the expression through the use of the buttons and tabs located below the expression box.

Expression

Enter the math expression in this box. The syntax is straightforward and based on the C programming language. The expression can contain any combination of functions and operators, absolute and/or variable grid names, dummies and numbers, spanning over multiple equations. The expression can either be directly typed in, or built using the supplied Variables, Operators and Functions tabs.

For further details see Expression Box under Application Notes.

Click this button to expand and display the available Operators and Functions with which to build the Grid Math Expression.

Use the keyboard to enter numerical values.

For more detailed information about the operators and functions of this expanded section, click on the links below:

Common Keys - Buttons consisting of the most commonly used operations and values are groups along the left, right below Operators and Functions.

Frequent Tab - Frequently used conditional and logarithmic operators and functions.

Special Tab - Special limit and mathematical functions.

Trig Tab - Trigonometry functions.

Statistics Tab - Statistical properties of one or more lines.

Click this button to add a new grid variable at the location of the cursor in the Expression box. The variable grid naming convention is G#, where # is the next available number.

This is not to be confused with temporary variables (see Common Keys), which only exist at run time and are not saved.

Step 2: Assign grids to the variable names used in the expression.

Assign grids

This box is populated with all the grid variables present in the Expression. Each variable can be set either by choosing a grid from the drop-down list of the grids used in the current project or through the browse button you can navigate and select the appropriate grid.

The tool distinguishes between input and output grids. Input grids must exist and are preceded by , while you can enter the output grid name.

For further details see Assign grids box under Application Notes.

Common tasks

To speed up building the expression, this drop-down list offers a number of simple common math expressions:

Add 2 grids: G0 = G1 + G2;

Divide 2 grids: G0 = G1 / G2;

Multiply 2 grids: G0 = G1 * G2;

Multiply grid by factor 2: G0 = G1 * 2;

Remove 5000 from grid: G0 = G1 - 5000;

Subtract 2 grids: G0 = G1 - G2;

True/False statement: G0 = (G1>5000) ? G2 :G3;

You can select an expression from the list and then if needed continue to further edit it.

  • An expression is parsed from right to left, so in the conditional expression G0 = (condition)?G2:G3, it is the data type of the rightmost channel, G3, that defines the data type of the output.

    • Expression file

    Once you have built the expression you can save it to file for future use. Similarly if you have previously saved expressions, you can load them from file.

    The expression files are simple ASCII text files and can be viewed outside of Oasis montaj using a text editor.

    		Click on Clear to clear all the entries, expression, grid assignment, and expression file.

    		Click on Apply to apply the expression without exiting the dialog. This button is useful when you intend to apply the same expression to multiple grids.

    Application Notes

    *The GX tool will search in the "...\Geosoft\Desktop Applications \gx" folder. The GX.Net tools, however, are embedded in the geogxnet.dll located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" folder, then supply the GX.Net tool in the specified format.

    If an equation yields a value outside the data range, the output at that point is set to DUMMY.

    Expressions are parsed from right to left, for example in the conditional expression G0 = (condition)?G2:G3 it is the data type of the rightmost channel, G3 that defines the data type of the output.

    Expression

    Longer, more complex expressions spanning over multiple lines will remain in view. As you add new rows to the Expression box, the height of the box automatically increases to show up to 12 lines upon which a scroll bar appears along the right margin of the expression box.

    To further increase the vertical height of the box, while the focus is on the expression box, hover the cursor over the top or bottom edge of the dialog until you see the double arrows. Then, click and drag the edge of the dialog, and the expression box will grow accordingly.

    When working with long expressions you can widen the dialog by hovering the cursor over the left or right edge of the dialog until you see the double arrow. Then, click and drag the edge of the dialog to the appropriate size.

    Assign Grids

    To further increase the vertical height of this box, while the focus is on the Assign grids box, hover the cursor over the top or bottom edge of the dialog until you see the double arrows, then click and drag the side of the dialog, and the Assign grids box will grow accordingly.

    You will not see the temporary variable listed in this window.

    See Also: