Grid Equation Transform

While the Grid-To-Grid Operations tool can handle most simple equations, the Grid Data Equation Transform is built to handle larger custom equations.

To open this tool, select Contours>Grids>Grid Equation Transform.  

Equation tab

The Equation tab sets the actual equation using variables and mathematical operators

The Grid Data Equation Transform Equation tab

The variable on the left side of the equal sign is the result grid, while variables to the right are the input grids and constants. Variables can either be very specific (such as “AVG_POROSITY” or “ISOPACH”) or general (such as “A” or “B”).

Equations entered here obey standard order of operations: Parenthesis, Exponents/Roots, Multiplication, Division, Addition, and Subtraction.

Basic Mathematical Operators:

+        Addition
-        Subtraction
*        Multiplication
/        Division
**        Exponent

Mathematical and Trigonometric Functions:

ABS(x)                Absolute value of x
ACOS(x)                Arccosine of x (in radians)
ASIN(x)                Arcsine of x (in radians)
ATAN(x)                Arctangent of x ( in radians)
COS(x)                Cosine of x in radians
COSH(x)                Hyperbolic cosine of x (radians)
EXP(x)                e to power of x
INT(x)                        Truncated value of x
LOG(x),LN(x)                Natural Log of x
LOG10(x)                Log based 10 of x
MAX(x,y)                Maximum of x and y
MIN(x,y)                Minimum of x and y
ROUND(x)                Rounded value of x
SIN(x)                        Sine of x in radians
SQRT(x)                Square root of x
SQR(x)                x squared
SINH(x)                Hyperbolic sine of x (radians)
TAN(x)                Tangent of x in radians
TANH(x)                Hyperbolic tangent of x (radians)

Options tab

The Options tab has a couple of options that mostly pertain to calculations involving isopachs.

The Grid Data Equation Transform Options tab

Substitute Zero For Nulls - This option causes null-valued grid values to be set to zero prior to executing the equation. A null value anywhere inside the equation generates a null result, which can create holes in a summed isopach.

Set Negatives to Zero - This option causes negative grid values to be set to zero prior to executing the equation. Summing negative values actually reduces the total footage, so it may be useful to substitute zero values for negative numbers.

Assign Z Data Equation Variables

After setting the variables, the next step is to assign grids and constants to the variables.

Setting variables to grids and constant. Before (Left) and after (Right)

Output Grid

Grid - This entry sets the name of the newly calculated isopach grid.  By default, Petra will create a grid using the variable name outlined in the equation, but users can enter a new name or select an existing grid to overwrite.

Title - This option sets the title of the new grid.

Equation Variable Assignments

This section sets which variables in the equation are which grids and constants. Select the equation variable on the Equation Variable Assignments list  and select the correct grid or constant.   Select the "Assign" button to finalize each variable.