Grid Data - Direct Gridding

Gridding refers to the process of interpolating data onto an equally spaced “grid” of cells in a specified coordinate system. For an introduction to gridding and a summary of the different gridding methods click here.

Direct Gridding

The direct gridding method creates a grid from data without using any interpolation. It is intended for use with highly sampled data and it provides a quick gridded view of it. When the input database is very large and the gridding process may become lengthy, it can be used to quickly produce the first draft grid for inspection. For over-sampled data such as LiDAR, GPR, or seismic data, it can be the preferred option.

The method simply places in each grid cell the average (or the minimum or maximum value) of the data that populates it. In the first case, the data within a cell is weight-averaged relative to their proximity to the grid node. No other processing is performed on the data (e.g., iterative calculations or splinning); cells that are void of data points remain blank.

Use the Grid Data option from the Grid and Image > Gridding menu to grid data using the direct gridding method.

Direct Gridding Options

Data to grid

Select the database channel to grid. To specify an array element, append to the channel array name the element index in square brackets. For example, Chan[1] would indicate the second element of the array channel "Chan".

Script Parameter: DIRECT_GRIDDING.CHANNEL

Output grid

Provide the name of the output grid file. This field is auto populated based on the active database and the selected channel to grid; however, you can override the default.

The default output grid format is selected automatically as the output file type. The type can be controlled using the browse dialog, which is accessible from the [...] button.

 Script Parameter: DIRECT_GRIDDING.GRID

Gridding method

The current gridding method is displayed.

Script Parameter: GRIDDING_TOOL.METHOD [4: Direct]

Cell size

Specify a cell size for the output grid. This field is auto-populated with the calculated default grid cell size and rounded to the nearest ten or hundred:

The grid cell size (the distance between grid points in the X and Y directions) should normally be ¼ to ½ of the line separation or the nominal data sample interval. If not specified, the data points are assumed to be evenly distributed, and the area rectangular. The default cell size is then defined by the following formula:

Where:

Script Parameter: DIRECT_GRIDDING.CELL_SIZE

Extents and Data
Spatial Extents

Grid extents
(X min, Y min,
X max, Y max)

Define the spatial limits of the area to be gridded. By default, these fields are set to the full extents of the current X & Y channels of the active database in order to include all the data in the database:

X min, Y min: the ground coordinates of the first grid point at the bottom left corner of the rectangular grid area (by default, the minimum limits of the input data file are used).

X max, Y max: the ground coordinates of the last grid point at the top right corner of the rectangular grid area (by default, the maximum limits of the input data file are used).

To grid a subset of the data, enter the limits of the bounding rectangle, or press the Draw Extents button to interactively define the boundary extents – the output grid coverage will extend to these limits.

Script Parameter: DIRECT_GRIDDING.XY

[Draw Extents]

Press this button to interactively define the grid boundary extents: in the Grid Preview pane, use the mouse to click & drag to draw a box, then release the mouse cursor to accept the final size of the box. The X & Y values will be updated in the Grid extents fields, and the preview window will be refreshed to show the newly defined extents.

  • You can draw the box in any of the four possible ways (e.g., from bottom left to top right).
    		•

    [Reset Extents]

    Press this button to reset the grid extents to the initial state of defaults for the active database.

    The Grid Preview pane (when Auto-refresh is enabled) will be updated to reflect the change; however, the zoomed state (in/out) of the grid preview will not be affected.
    Data Filtering

     

    Mask channel

    Select a channel from the drop-down list to act as a mask.

    Only database channels that have the class property set as "MASK" are listed. Additionally, string channels and channels with array size greater than 1 are omitted from the list.

    The data values in the selected Data to grid channel with corresponding dummy (*) values in the Mask channel will not be used in the gridding process.

    The X & Y values will be updated in the Grid extents fields to reflect the masked data, and the generated masked grid (with the correct extents) will be automatically rendered in the Grid Preview window (the Auto-refresh option must be selected). 

    Script Parameter: DIRECT_GRIDDING.MASK_CHANNEL

    Interpolation
    Direct

     

    Cell value

    Individual grid cell values are assigned using the select statistic on all data values falling within that cell. The following options are available: 

    • minimum value
    • maximum value
    • mean value
    • number of (valid, non-dummy) items in a cell
    You can create a grid of the density of sample locations, rather than the value recorded at each location. This gridding option is useful for determining the spatial distribution of highly sampled data and enables you to easily identify areas which are undersampled.

    Script Parameter: DIRECT_GRIDDING.GRID_VALUE [0: minimum, 1: maximum, 2: mean, 3: number of items, Default: 0]

    Set zero values to dummies

    This option becomes enabled when the Cell value option is the “number of items in a cell”.
    If checked, the cells for which no data values were found are given dummy values, so they won’t show up in the Grid Preview pane or when the grid is displayed from the Project Explorer.

    Script Parameter: DIRECT_GRIDDING.DUMMY_ZEROS [0: No, 1: Yes, Default: 1]
                                                       

    [Restore Defaults]

    This button remains disabled until any of the fields default values are changed. Press the button to reset the gridding parameters to the initial state of defaults for the active database.

    When Restore Defaults is clicked:

    The following parameters are reset to their default values:

    • The cell size value
    • All the parameters on both the Extents and Data and Interpolation tabs
    • Only the parameters for the current gridding method are affected.

    The following parameters are not reset:

    • The data to grid selection
    • The output grid file name
    • The gridding method

    The Grid Preview (with Auto-refresh enabled) and Variogram panes will be updated to reflect any parameters changes; however, the zoomed state (in/out) of the grid preview will not be affected.

    Application Notes

    Once a gridding task is executed, the gridding options are retained when switching between different databases. The Grid Data tool will recall the previous gridding parameters associated with the current database, regardless of whether gridding tasks have been performed on different databases since.