Channel Math

Use the Database Tools > Channel Math menu option (geogxnet.dll(Geosoft.GX.Math Expression Builder.Math Expression Builder;RunChannel)*), to create, save, load and execute math expressions for your Channel data. This easy-to-use standardized dialog provides all the math expression options on a single tabbed dialog.

The option is also available with the UAV Merge Sorties extension under the UAV Merge Sorties > Pre-processing menu.

Channel 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 channel 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 toggle button to expand and display the available Operators and Functions with which to build the channel 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. String Tab - String functions. This tab is only visible if your database contains channels of type String. Trig Tab - Trigonometric functions. Statistics Tab - Statistical properties of one or more lines. Offset Tab - Operators to access channel values on rows other than the current one. Date Tab - Convert Julian Date (day, month, year) to Geodate (fractional years) or vice versa. Time Tab - Convert Time (second, minute, hour) to Geotime (fractional hours) or vice versa.
	Click on this button to add a new channel variable at the location of the cursor in the Expression box. The variable channel naming convention is C#, 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 read from or saved to the database.
Step 2: Assign channels from the current database to the variable names used in the expression.
Assign channels	This box is automatically populated with all the channel variables present in the Expression. Select from the drop-down list the appropriate channel name to assign to each of the variables in the expression. The drop-down list is populated with the channel names from the current database. The tool distinguishes between input and output channels. Input channels are preceded by and must be selected from a drop-down list, while output channels can be both selected from a list of existing channels and entered manually as a new channel name. For further details, see Assign channels 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 Channels: C0 = C1 + C2; Divide 2 channels: C0 = C1 / C2; Multiply 2 channels: C0 = C1 * C2; Multiply channel by factor 2: C0 = C1 * 2; Remove 5000 from channel: C0 = C1 - 5000; Subtract 2 channels: C0 = C1 - C2; True/False statement: C0 = (C1>5000) ? C2 :C3; You can select an expression from the list and then if needed, continue to further edit it.
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, channel 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 channels in the same database.

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 is set to DUMMY.

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. After 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 Channels

When building the expression, instead of using variables and assign a channel to each variable, you can also use channel names as they appear in the current database. You will not be prompted for these in the Assign channels box

Similarly, you will not be prompted for the potential temporary variable present in the expression.

To further increase the vertical height of this box, while the focus is on the Assign channels 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 channels box will grow accordingly.

If the output channel does not exist, it will be created to be of a logical data type.

If the variable(s) in the conditional expressions are of different types, the equation parser will define the output type according to the left most variable. This may not be your intention. If the output data type cannot be reasonably determined by the equation parser, the output channel will be populated with dummies.

Array Data

Array data is now supported in the Channel Math Expression Builder. The desired elements of an array can now be placed within square brackets, for example, you could have the following expression,
CO=C1[1]+C2[5].

The elements of an Array are now supported by the Offset dot (.) functions and Statistics dot (.) functions.

Special Functions

Table lookup functions, although supported are not directly offered as a choice under the function tabs and cannot be executed from within the Math tools but can be executed within the Spreadsheet Window.