Once an interpolation scheme has been selected and the appropriate parameters for the selected scheme have been input, the data set of the active scatter point set can be interpolated to another object. During the interpolation process, a new data set is constructed for the target object containing the interpolated values.
A separate interpolation command is provided for interpolating to each of the target objects. The interpolation commands are found in the Interpolation menu. The commands are as follows:
The to Active TIN command interpolates the active 2D scatter point set to the vertices of the active TIN using the current interpolation options.
When the to Active TIN command is selected, the Interpolate dialog appears.
The to 2D Mesh command interpolates to the nodes of the active 2D scatter point set to the nodes of the 2D finite element mesh using the current interpolation options.
When the to 2D Mesh command is selected, the Interpolate dialog appears.
The to 2D Grid command interpolates the active 2D scatter point set to the 2D finite difference grid using the current interpolation options. The interpolation is done either to the grid nodes or to the grid cell centers depending on whether the grid is a mesh-centered or cell-centered grid.
When the to 2D Grid command is selected, the Interpolate dialog appears.
The to 3D Mesh command in the 2D Scatter Point module interpolates the active 2D scatter point set to the nodes of the 3D finite element mesh using the current interpolation options. Since the interpolation is two-dimensional, the Z coordinate of the mesh nodes is ignored during the interpolation process.
When the to 3D Mesh command is selected, the Interpolate dialog appears.
The to 3D Grid command in the 2D Scatter Point module interpolates the active scatter point set to the 3D finite difference grid using the current interpolation options. The interpolation is done either to the grid nodes or to the grid cell centers depending on whether the grid is a mesh-centered or cell-centered grid. Since the interpolation is two-dimensional, the Z coordinate of the nodes or cells is ignored during the interpolation process.
When the to 3D Grid command is selected, the Interpolate dialog appears.
The to MODFLOW Layers command is used to interpolate layer elevations and starting heads to the layer arrays in the BCF package of a MODFLOW simulation. Using this command, all of the layer data can be interpolated in a single step. This command can only be used when the "true layer" elevation method is selected for the MODFLOW simulation.
The first step in using the to MODFLOW Layers command is to create a scatter point set with a data set for each of the desired layer arrays. The simplest way to accomplish this is by creating a tabular scatter point file. A tabular scatter point file can be created using a text editor or spreadsheet program. A sample tabular scatter point file describing layer elevations and starting heads for a three layer MODFLOW model is shown below. Note that the top elevation is defined only for the top layer. For all layers, a bottom elevation is defined. It is assumed that the top elevation of a layer is equal to the bottom elevation of the layer above. The tabular scatter point file is imported using the Import command in the File menu.
|
x |
y |
top1 |
bot1 |
bot2 |
bot3 |
starthd |
|
360 |
1670 |
450 |
345 |
200 |
100 |
1010.5 |
|
290 |
870 |
445 |
340 |
195 |
95 |
1007.2 |
|
480 |
420 |
450 |
350 |
200 |
100 |
1004.0 |
|
620 |
2120 |
455 |
245 |
200 |
100 |
1009.9 |
|
990 |
1820 |
470 |
355 |
210 |
115 |
1012.6 |
|
890 |
1190 |
465 |
350 |
205 |
110 |
999.2 |
|
1030 |
710 |
475 |
360 |
215 |
130 |
1002.6 |
|
910 |
590 |
470 |
350 |
210 |
125 |
1005.5 |
|
1520 |
2100 |
530 |
405 |
275 |
185 |
1003.8 |
Sample Tabular Scatter Point File for MODFLOW Layer Data.
Once the scatter point file has been imported the MODFLOW simulation must be initialized, and an interpolation technique has been chosen, the to MODFLOW Layer command can be selected. When the command is selected, the Interpolate to MODFLOW Layers dialog appears. The options in the dialog are as follows:
The list in the upper left section of the dialog displays all of the data sets associated with the active 2D scatter point set. The list on the upper right side of the dialog contains the names of the MODFLOW layer data arrays. Each data set on the left is associated with one of the layer data arrays on the right. This association is accomplished by selecting one item from each list and selecting the Map button. The "mapped" relationships are displayed in the bottom portion of the dialog. An association can be broken by selecting the relationship in the list on the bottom and selecting the Unmap button.
When the Interpolate to MODFLOW Layers dialog is first brought up, GMS scans through the list of data set names and attempts to automatically match the data sets to the appropriate MODFLOW layers. As long as each elevation data set name contains "top" or "bot" and a number in the data set name, GMS will automatically map the data set to a MODFLOW layer array. For the starting head array, the name should contain "start" or "hd" or "head."
The 'Apply starting heads...' options at the bottom of the Interpolate to MODFLOW Layers dialog are used to control how the starting head values are loaded into the Starting Heads array. If the Apply starting heads to variable head cells only option is selected, the interpolated head values are not assigned to specified head cells (cells with a negative IBOUND value). This option is typically used when the interpolated head values are simply being used to provide a good initial condition for the model and a different means has been used to specify the starting head values at specified head boundaries. The Apply starting heads to all cells option is useful when performing a regional to local model conversion. In this case, the heads being interpolated are computed heads from a regional model. These head values are used directly by the specified head cells at the boundaries.
Once the relationships are defined, the OK button can be selected to begin the interpolation process. Each of the scatter point data sets is interpolated directly to the selected MODFLOW array and the entire set of interpolation operations are carried out in one step.
In some cases, it is useful to perform the MODFLOW layer interpolation in multiple steps. For example, the layer data may be imported to GMS using three scatter point sets: one for the starting head data (from observation wells), one for the top elevations of layer 1 (from a terrain map), and one for the bottom elevations of the remaining layers (from borehole data). In this case, the to MODFLOW Layers command can be executed three times, each time with the appropriate active scatter point set.
Once the layer elevations are interpolated, they should be checked for errors prior to saving and running the MODFLOW simulation. It is common for unexpected overlaps (the top elevation is below the bottom elevation for a particular layer). Layer errors can easily be detected using the MODFLOW Model Checker. The Model Checker dialog includes a customized set of tools for automatically fixing layer elevation errors. The Defining Layer Data tutorial in the GMS Tutorials document gives several examples of how the layer interpolation command in the layer error editing tools can be used to model complicated stratigraphic relationships such as pinchouts, embedded seams, and bedrock truncation.
When one of the interpolation commands is selected, the Interpolate dialog appears.
Related Links:
Interpolating with 2D Scatter Points