Edit existing area
This function allows you to directly enter the parameters that define your grid mesh.
To run this function: Choose Surfaces > Contouring > Contouring area > Edit existing area, or...
The grid is defined by the x (easting) and y (northing) values of:
(a) The grid origin (the origin being the bottom-left-hand-corner of the grid in a ZOOM ALL, ie looking directly from above, view);
(b) The grid extents;
(c) The grid step sizes.
You can also define an angle of grid orientation in the xy plane (the grid can be rotated arbitrarily in the xy plane about the grid origin). The z coordinate of the grid origin must also be entered on the form but it is purely for display purposes to enable the grid coverage to be displayed at a representative z value.
In more detail, the angle of grid orientation is defined as follows: The grid will be rotated about the grid origin in the xy plane. The angle should be between 0 and 360. When in a ZOOM ALL (that is, looking directly form above) view, the angle is measured relative to the y (northing) axis with clockwise being positive.
To set up the parameters for a new grid you can either use the Layer Defaults button on the CREATE GRID menu to set default values for the grid mesh parameters based on the spread of the data in a defined graphics layer, or you can directly enter the parameters using this function. The first approach is quick and easy, the second approach gives you more control. The recommended way to directly enter the parameters for a new grid is as follows:
(i) Use the Draw/Erase button on the CREATE GRID menu to display the Draw/Erase menu. Then use the 2D Grid button on the Draw/Erase menu to overlay a 'graphics grid' on the initial data. Use this to visually estimate candidate values for the Grid Model origin and extents etc;
(ii) Go back to the CREATE GRID menu, press the PARAMETERS Edit Mesh button, and fill in the ENTER GRID MESH PARAMETERS form with the candidate values;
(iii) Applying the ENTER GRID MESH PARAMETERS form will display the grid coverage on the screen. The grid coverage is represented by 4 points showing the 4 corners of the grid mesh you have defined. These 4 points are stored in a closed clockwise segment in the graphics layer grid_coverage, and this layer can be saved to a string file. You may wish to type ZOOM ALL to get a better view of your data and grid coverage;
(iv) You will find that with some fine tuning with the PARAMETERS Edit Mesh button you will be able to easily create a grid with exactly the coverage you require BEFORE you commence any potentially lengthy interpolation or contouring calculations. You can also use the COVERAGE Create View and COVERAGE Delete View buttons to toggle on and off the view of the grid coverage;
(v) Only when you have visually confirmed that you have a grid you are happy with, do you then press the Process Grid button to begin interpolating into the grid and extracting contours.
Maximum Grid Resolution
For those users familiar with the Surpac Block Model, the Grid Model is stored internally as a 2 dimensional analogy of the Block Model and its maximum resolution is calculated in a similar way. The calculations involve the x and y step sizes and extents. Internally the grid is stored at a resolution of 2 to the Nth power where N ranges from 1 to 14. That is the internal resolution will be at one of 2, 4, 8, 16, 32, 64, 128, 512, 1024, ..., 16384. Which of these is used for your particular grid is chosen using the maximum of the ratios of (x extent/ x step size) and (y extent/ y step size). The following two examples show how this works:
(1) You have defined an x extent of 1000 and a x step size of 1 and a y extent of -2000 and a y step size of 1. Here the (y extent/ystep size) ratio is the largest at 2000. The grid is therefore stored internally at the smallest available resolution that is also sufficiently large, ie 2048.
(2) You have defined an x extent of 10000 and a x step size of 1 and a y extent of 20000 and a y step size of 1. Here the (y extent/ystep size) ratio is the largest at 20000. However this resolution exceeds the maximum available (ie 16384), in this case you will receive a warning message that you have exceeded the maximum allowable grid resolution (NB this warning will appear at the stage that you actually create the grid by hitting the Process Grid button on the CREATE GRID menu).
Note:The Grid Model implementation is based on the graphical display of input data and output results. It is therefore highly recommended that you recall the string file that contains the data you wish to use in the interpolations into the current graphics layer as a preliminary step for the calculations. If you have not already done so, you should do this by using the RECALL FILE function present in the CREATE GRID menu.
Y coordinate of grid origin
Enter the y (northing) coordinate of the grid origin. The origin is the bottom left hand corner of the grid in a ZOOM ALL (that is, looking directly form above) view.
X coordinate of grid origin
Enter the x (easting) coordinate of the grid origin. The origin is the bottom left hand corner of the grid in a ZOOM ALL (that is, looking directly form above) view.
Z coordinate of grid origin
Enter the z coordinate of the grid origin. This is purely for display purposes to enable the grid coverage to be displayed at a representative z value.
Y extent of grid
Enter the y (northing) extent of the grid.
X extent of grid
Enter the x (easting) extent of the grid.
Y grid step size
Enter the y (northing) step size for the grid.
X grid step size
Enter the x (easting) step size for the grid.
Angle of grid orientation
Enter angle of grid orientation in the xy plane. See above for details.
Result
Once the form is applied the 4 points representing the 4 corners of the grid coverage are displayed in a closed clockwise segment on the screen in the graphics layer grid_coverage. You may wish to type ZOOM ALL to get a better view of the original data and the grid coverage.