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iMOD User Manual version 5.2 (html)


4.1Create an IDF-file

IDF-files can be created from scratch or by conversion from different formats. The available options are:

To create a new IDF select the main option Edit, choose Create Feature, then IDFs from and then one of the options shown above.

When creating a new IDF from scratch then the IDF is created with NoData values. When creating an IDF from the other formats then the IDF cells are assigned values derived from these files.

Option Scratch, Create IDF window:

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Zoom Level

Click this button to adjust the IDF extent to the current zoom level in the graphical display.

XLLC / XURC (m) :

Enter the X coordinate for the lower-left-corner (XLLC) and upper-right-corner (XURC) of the IDF extent.

YLLC / YURC (m) :

Enter the Y coordinate for the lower-left-corner (YLLC) and upper-right-corner (YURC) of the IDF extent.

CellSize (m) :

Enter the cellsize of the IDF in meters.

NOTE: The values for XLLC, YLLC, XURC and YURC will be trimmed automatically to the CellSize value.

Nrows/Ncols:

Displays the number of rows and the number of columns for the current IDF extent. These values are computed automatically and can not be changed directly.

NoDataValue:

Enter the NoDataValue for the IDF

Apply

Click this button to start the creation of the IDF

Close

Close the Create IDF window. The new IDF is added to the iMOD Manager window.

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Figure 4.1: Create IDF window, IPFs tab


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Open Map
Click this button to open an IPF-file.

IPF-name:

Displays the name of the IPF-file.

X-coordinate:

Specify a column in the IPF-file that represents the X coordinate

Y-coordinate:

Specify a column in the IPF-file that represents the Y coordinate

Attribute to be gridded:

Specify a column in the IPF-file that represents the values to be gridded. Only numeric values can be gridded.

Zoom Level

Zoom Level
Click this button to adjust the IDF extent to the current zoom level in the graphical display.

IPF Extent

IPF Extent
Click this button to adjust the IDF extent to the entire extent of the selected IPF-file.

XLLC / XURC (m) :

Enter the X coordinate for the lower-left-corner (XLLC) and upper-right-corner (XURC) of the IDF extent.

YLLC / YURC (m) :

Enter the Y coordinate for the lower-left-corner (YLLC) and upper-right-corner (YURC) of the IDF extent.

CellSize (m) :

Enter the cellsize of the IDF in meters.

NOTE: The values for XLLC, YLLC, XURC and YURC will be trimmed automatically to the CellSize value.

Nrows/Ncols:

Displays the number of rows and the number of columns for the current IDF extent. These values are computed automatically and can not be changed directly.

NoDataValue:

Enter the NoDataValue for the IDF.

Duplicate Points

Select one of the options for points with identical coordinates:
Sum: use the sum of the values to be gridded
Mean: use the mean of the values to be gridded.

Method:

Select one of the interpolation methods (see for batch creation of IDF’s 8.2.10):

(SPP) Simple Point Sampling:
Click this option to determine grid values on those points that are inside the current grid cell only. As a result, it might be that many grid cells getNoDataValues.

(BI) Bivariate Interpolation:
Click this option to determine grid values from a smooth interpolation function Z(x,y), which agrees with the given data (Hiroshi Akima, A Method of Bivariate Interpolation and Smooth Surface Fitting for Values Given at Irregularly Distributed Points, ACM Transactions on Mathematical Software, Volume 4, Number 2, June 1978).

PCG (Preconditioned Conjugate Gradient):
Click this option to apply the Preconditioned Conjugate Gradient method (this is the same as the solver used in MODFLOW)

VG (Variogram):
Click this option to create a semivariogram; this yields no interpolation of the data, it generates a table filled in with a variogram. The results will be written in the VARIOGRAM.TXT file.

(SKI) Simple Kriging Interpolation:
Click this option to apply a Kriging interpolation assuming a constant mean over the entire domain.

(OKI) Ordinary Kriging Interpolation:
Click this option to apply a Kriging interpolation assuming a constant mean in the neighborhood of each estimation point.


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Open settings window
This function is active for the interpolation methods PCG, SKI and OKI.


Solver Settings window for PCG interpolation:

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Outer
Iterations

Specify the maximum number of outer iterations used by the PCG solver;

Inner
Iterations

Specify the maximum number of inner iterations used by the PCG solver. The more inner iterations used for a linear problem, the faster a PCG solution will be achieved;

Head Closure
Criterion

Specify the closure criterion (e.g. Heads) for the problem to be solved. This value related to the units of the problem to be solved, choose a value at least two order of magnitude less than the desired accuracy;

Waterbalance Closure
Criterion

Specify the closure criterion for the water balance for the problem to be solved, e.g. the lumped error of accuracy in the head. This value related to the units of the problem to be solved, choose a high value whenever the usage of the Head Closure Criterion is sufficient;

No. Inner
Solutions

Specify an acceptable value, e.g. 25, whenever the problem to be solved shows high non-linearities that avoid any convergence of the solver. Solving a Solid might introduce these non-linearities that can be tackled in this manner;

Relaxation Factor

This factor damps the subsequent solutions of the solver. Use a high value (1.0) for linear problems and a lower value for non-linear problems. Use the Use Adaptive Damping option for non-linear problems instead;

Adaptive Damping

Apply this for non-linear problems as it will adapt the Relaxation Factor during the iteration process to yield a more robust solution;

Boundary Conditions

Select the Tight option to fixate the known location during the solution, use Loose instead to use a different approach in which the known areas are simulated by a boundary condition that allows more change on the known areas;

OK

Select this button to agree with the entered values.


The PCG solver is available in an iMOD Batch functionality as well, see for more information 8.2.10. NOTE: Consult scientific literature regarding PCG solver settings as described above.


Kriging Settings window for Simple and Ordinary Kriging interpolation:

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Use minimal
number of
Points

Specify the minimum number of points (per quadrant).

Increase
Range to
reach minimal
number of
Points

Select this option to allow the search increase the Range whenever the number of points is less than the entered minimal number of points.

Apply Quadrant

Select this option to devide the number of points in quadrant to met the minimal number of points individually.

SILL

Specify the SILL value. The value that the semivariogram model attains at the range (the value on the y-axis) is called the sill. The partial sill is the SILL minus the NUGGET.

RANGE

Specify the RANGE value. When you look at the model of a semivariogram, you’ll notice that at a certain distance, the model levels out. The distance where the model first flattens out is known as the range. Sample locations separated by distances closer than the range are spatially autocorrelated, whereas locations farther apart than the range are not.

NUGGET

Specify the NUGGET value. The nugget effect can be attributed to measurement errors or spatial sources of variation at distances smaller than the sampling interval or both. Measurement error occurs because of the error inherent in measuring devices. Natural phenomena can vary spatially over a range of scales. Variation at microscales smaller than the sampling distances will appear as part of the nugget effect. Before collecting data, it is important to gain some understanding of the scales of spatial variation. Increased smoothness is applied whenever the NUGGET value is increased.

Semivariogram

Specify the type of Semivariogram, select from:

  • Linear Model:
    \(g(h)=c_0+c_1*\frac {h}{a}\)

  • Spherical Model:
    \(g(h)=c_0+c_1*1.5\frac {h}{a}-0.5(\frac {h}{a})^3\)

  • Exponential Model:
    \(g(h)=c_0+c_1*(1-\exp (-3\frac {h}{a}))\)

  • Gaussian Model:
    \(g(h)=c_0+c_1*(1-\exp (-3\frac {h^2}{a^2}))\)

  • Power Model:
    \(g(h)=c_0+c_1*h^{0.5}\)

\(h\) represents the lag distance, \(c_0+c_1\) is the SILL value, \(c_0\) is the NUGGET value and \(a\) is the range.


Kriging is also available in an iMOD Batch functionality, see for more information 8.2.10. NOTE: Consult scientific literature regarding Kriging Settings as described above.

Force Line Interpolation

Not active for IPFs.

Apply

Click this button to start the creation of the IDF.

Example of a Simple Point Sampling interpolation:

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Example of a Bivariate interpolation:

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Create IDF window, GENs tab:

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Click these buttons to draw, open, save, delete or rename a shape. More detailed information can be found in figure 4.1.

IDF Extent

Specify the extent and dimensions of the IDF and the interpolation method. See the description for the IPFs tab for an explanation.

Force Line
Interpolation

Create interpolated raster cells only along the lines as specified in the GEN

Apply

Click this button to start the creation of the IDF

Note: The value for a raster cell will be determined by the polygon number. The value of raster cells that are part of overlapping polygons will be equal to the mean value of the polygon numbers. NoDataValues are assigned to raster cells outside any polygon.

Example of a polygon GEN translated into an IDF-file:

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Example of a line GEN translated into an IDF-file:

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The above example shows the rasterizing of lines into an IDF-file. The result is an IDF-file with the number of the different lines and another IDF showing the length of the line in each rastercell crossed by it.

Create IDF window, IFFs tab:

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Open Map
Click this button to open an IFF-file.

Attribute

Select one of the options to grid:
PARTICLE_NUMBER – number of the particle
ILAY – modellayer number
XCRD – x coordinate
YCRD – y coordinate
ZCRD – z coordinate
TIME(YEARS) – elapsed time in years
VELOCITY – velocity (m/day)

while

Click this checkbox to use an extra logical expression. Choose one of the options (see under Attribute) and specify a logical operator (“=”;”\(<\)\(>\)”;”\(<\)”;”\(<\)=”,”\(>\)”;”\(>\)=”) and numeric value.

IDF Extent

Specify the extent and dimensions of the IDF and the interpolation method. See the description for the IPFs tab for an explanation.

Force Line
Interpolation

Not active for IFFs

Apply

Click this button to start the creation of the IDF

Note: The value for a raster cell will be determined by the particle that passes through. Whenever more particles pass through the same rastercell, a mean value for the chosen attribute will be computed.

Example of a result of a particle simulation (left) gridded into a single IDF-file (right) for those parts that are within modellayer 3 only:

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