# iMOD User Manual version 5.2 (html)

#### 11.3Tutorial 2: Map Operations

This tutorial gives an introduction to several map operations using IDF-files. See for more detailed references section 6.7.

Outline

This is what you will do:

• • Calculate differences between two IDF-files;

• • Assign values to an IDF-file, conditionally;

• • Perform an up- and or downscaling of the cell size for an IDF-file.

Required Data

For this tutorial you need the following iMOD Data Files (IDF):

• • TOP_LAYER3.IDF;

• • BOTTOM_LAYER3.IDF;

• • T-VALUE_LAYER3.IDF.

All these files are located in the folder: {installfolder} \tutorials \TUT_DATA_MAP_OPER.

Note: {installfolder} refers to the full path of the directory you installed iMOD in (e.g. D:\iMOD).
Note: If you are a left-handed person and you converted your mouse button settings, ’left mouse button’ should be ’right mouse button’ and vice versa in these tutorials.

Getting Started

• 1. Launch iMOD by double clicking the iMOD executable in the Windows Explorer, and start with Create a new iMOD Project.

• 2. Go to View in the menu bar and select the iMOD Manager (or use the shortcut Ctrl+M).

Calculate Layer Thickness

Quite often it is necessary to compute the difference between two maps. In this example we compute the thickness of a particular model layer. We start by opening the files: TOP_LAYER3.IDF, BOTTOM_LAYER3.IDF from disk.

• 3. Click the Open IDF button (   ) from the Maps tabs on the iMOD Manager.

• 4. Select the above mentioned files in the Open File window. Go to the folder where the tutorial material has been installed.

• 5. Click the Open button.

After the files have been opened, those files will be added to the list of opened iMOD files in the iMOD Manager. iMOD does not modify the zoom extent, so we need to instruct iMOD to zoom on the loaded IDF files.

• 6. Click the zoom button   to zoom to the full extent of the IDF file.

Let us compute the thickness of model layer 3.

• 7. Click on the maps TOP_LAYER3.IDF and BOTTOM_LAYER3.IDF as they appear in the iMOD Manager, while pressing the Ctrl button.

Alternatively, you can select those files by left click your mouse and drag your mouse position over the files. If necessary, deselect those files that are undesired by clicking your left mouse button in combination with the Ctrl button.

• 8. Click on the iMOD Calculator button (   ) on the Maps tab of the iMOD Manager to enter the Map Operations window.

The selected IDF-files (inputfiles) will be filled in (Map A and Map B), as well as the outputfile (Map C). On default the output file will be saved in the folder: {IMOD_USER} \TMP \DIFF.IDF. The default equation (Formulae is [C=A-B]) subtracts the first IDF minus the second IDF, in the order in which those IDF-files will appear in the iMOD Manager. Whenever your BOTTOM_LAYER3.IDF is mentioned before the TOP_LAYER3.IDF in the iMOD Manager, you have to change the Formula into [C=B-A].

• 9. Enter [C=B-A] at the Formula.

• 10. Change the output file DIFF.IDF into THICKNESS3.IDF, so enter this name in the field specified behind Map C.

In the lower part of the window 3 options are given to define the size of the IDF to be created.

• 11. Select the option Map A.

This allows the size of the THICKNESS3.IDF to be exactly the size of the first mentioned IDF in the formula (A in this case). Whenever you need results for the current zoom extent only, click the option Window instead, this will speed up the calculation since only a part of the selected maps (Map A and Map B) will be subtracted.

• 12. Click the Compute … button.

The computed difference between the files TOP_LAYER3.IDF and BOTTOM_LAYER3.IDF will be saved in the TMP folder of your IMOD_USER environment by the name THICKNESS3.IDF. iMOD has added that file to the iMOD Manager, automatically.

Let us check the result.

• 13. Select the maps TOP_LAYER3.IDF, BOTTOM_LAYER3.IDF and THICKNESS3.IDF from the iMOD Manager.

• 14. Select the Map Value button (   ) on the Map tabs on the iMOD Manager window to start the Map Value window.

• 15. Check the results by moving your mouse around the graphical display.

• 16. Stop this inspection by right clicking your mouse somewhere on the graphical display.

Since this kind of visual inspection is rather easy to use, it is recommended to use it frequently to check any computations.

• 17. Select the Map Info button (   ) to inspect some simple statistics for THICKNESS3.IDF. Observe that the history of the THICKNESS3.IDF is saved and that the content is shown in the Additional Information box.

• 18. Click the Statistical button (   ) to get some statistical characteristics of the data.

Calculating Permeability

Each resulting IDF can be used subsequently for other map operations.

• 19. Open the T-VALUE_LAYER3.IDF by clicking the Open IDF button (   ) and select this file from the {installfolder}\TUTORIALS \TUT_DATA_MAP_OPER.

• 20. Select the maps T-VALUE_LAYER3.IDF and the THICKNESS3.IDF from the iMOD Manager.

• 21. Select the IDF Calculator ) and change for Map C the IDF-file DIFF.IDF into K-VALUE_LAYER3.IDF.

• 22. Enter the formula: [C=A/B].

All values in Map A (T-VALUE_LAYER3.IDF) will be divided by the values of Map B (THICKNESS3.IDF). If map A and map B are reversed, the equation can be entered as [C=B/A] without interchanging the IDF name next to the field Map A and Map B.

• 23. Select the option Window and click the Compute button; in this manner we will compute the permeability only for the current zoom extent.

To decrease computational times, map operations can be computed for the current zoomlevel on the graphical display only. The resulting IDF will have dimensions equal to the zoom level, however, cellsizes will be copied from the first mentioned IDF in the equation.

• 24. Check the result again with Map Value ).

Bear in mind that the computed legend classes are initially based on the minimum and maximum values of the IDF-file(s). Whenever you do not see much detail on the map, those minimum and maximum values might be far apart from each other. Apply a Percentile legend or click the Histogram button (   ) on the Stretched tab) on the Adjust Legend window. Looking at this graph can provide you with more insight in the colour distribution of your legend. Handling legends has been described in more detail in Tutorial 1.

Conditioned Map Operation

IDF Edit is a tool in which map operations can be applied for a particular selection of cells. In this tutorial a simple example is demonstrated. Suppose a map is required that shows all areas of the third model layer that have a thickness of more than 25 meter.

First we make an empty copy of THICKNESS3.IDF and name it THICKNESS3_25.IDF.

• 25. Enter the Map Calculator with THICKNESS3.IDF, enter the equation [C=0.0*A] and enter a filename for Map C to be THICKNESS3_25.IDF.

• 26. Click the Compute … button.

By means of the Map Calculator it is easier to make copies of IDF-files, rather than using the Windows Explorer, since the content can be blanked out and/or the resulting IDF can be resized (use the option Window or the optionx1,y1,x2,y2 where you can specify specific coordinates yourself).

Next step is to enter IDF Edit.

• 27. Select the option IDF Edit from the IDF Options menu from the Map menu.

It is not relevant what IDF is (de)selected in the iMOD Manager, since all IDF-files that are inside the iMOD Manager can be manipulated in IDF Edit. Important is to specify an IDF that operates as a template. All mids of raster cells inside that particular IDF will be used to store any selection. Please be aware of the fact that a coarse IDF used as a template, will not make adjustments to a finer IDF.

• 28. If not already selected, select THICKNESS3_25.IDF from the dropdown menu Use selected IDF to store selected cells.

• 29. Click the Select button to open the IDF Edit Select window.

• 30. Select the IDF-file THICKNESS3.IDF from the dropdown menu by Evaluate IDF A:.

• 31. Specify the Logic operator to be [$>$].

• 32. Enter a Value of [25].

• 33. Click the Get Selection button and observe that 97088 cells are selected out of 272000.

The current selection will be displayed as filled rectangles. Especially whenever a large selection needs to be displayed it can take a while.

• 34. Click the option Show Selection ) to turn the selection on or off.

A selection is stored on disk in the {IMOD_USER} \TMP folder. For iMOD-user a specific filename will be used, {USERNAME}SELECTED{i}.DAT. These files will store the current (i) and previous selections (i-?). As long as these files exist, iMOD can undo a selection (i>1).

• 35. Close the IDF Edit Select window.

• 36. Click the Calculate button in the IDF Edit window to open theIDF Edit Calculation window.

This window offers several functions to adjust values in IDF-files of the current selection.

• 37. Select the option Take From and select THICKNESS3.IDF from the dropdown menu.

• 38. Select the THICKNESS3_25.IDF from the dropdown menu at the menu field Assign Value TO.

• 39. Click the Calculate button.

The iMOD Manager can be used whenever the IDF Edit Calculate window is active. Let us check whether the computation has been carried out correctly.

• 40. Select the maps THICKNESS3.IDF and THICKNESS3_25.IDF in the iMOD Manager, click the redraw button (   ) and click the Map Value button (   ). Inspect the values.

As long as the IDF Edit Calculation window is active, any computation to any IDF can be undone.

• 41. Click the Undo Calculation button (   ) in the IDF Edit Calculation window to undo the computation. Repeat step 39. to compute the values again.

• 42. Click the Close button and confirm the next window.

Let us see what other method can be used to make a selection and/or calculation.

• 43. Clear the current selection by clicking the Clear button in the IDF Edit window. Accept the following window stating whether you’re sure to delete the selection.

• 44. Click the Trace button.

• 45. Select the option [Greater than selected value] in the Values should be option.

• 46. Leave the option Search Criterium selected for [5 Point] which means that iMOD will search connecting cells that are connected on a five-point stencil.

This option allows you to make a selection that is determined by the location that you will select on the graphical window for all cells that have values greater than the value at the selected point. The selection should be connected to each other which makes it quite different from the previous selection method. Let us do that.

• 47. Click on the button Select Location on Map .. and select a cell from which a selection should be made that have greater values. Click your left mouse button. Please note that it may take a while to get the selection.

Finally we can adjust the current selection by means of a drawing functionality that allows you to interactively draw regions to add to the selection and/or remove from the current selection.

• 48. Click the Close button on the IDF Edit Pipet window to close it.

• 49. Select the Draw option in the IDF Edit window.

• 50. Choose the option Remove Cells from the IDF Edit Draw window.

• 51. Move over the cells you want to remove by holding down your left mouse button. Observe what is happening, try to add cells to the selection too.

• 52. Click the Close button.

• 53. Close the IDF Edit window by clicking its Close button too.

Map Scaling One of the great options of iMOD is its ability to rescale data files. A variety of up- and downscaling algorithms have been implemented. In this example we will rescale the top elevation of a model layer from a cell size of 100 x 100 meter into a cell size of 1000 x 1000 meter.

• 54. Select the map TOP_LAYER3.IDF from the iMOD Manager.

• 55. Enter the Map Calculator ).

• 56. Select the Scale/Size tab.

On this particular tab, a variety of up- and downscaling options are available by the menu fields Upscale Formulae and Downscale Formulae.

• 57. The resulting IDF will be saved in the same folder as the TOP_LAYER3.IDF and will be called TOP_LAYER3_SCALED.IDF. We accept this default output name.

• 58. Enter a gridsize of 1000 meter in the Scale field.

• 59. Select the option Arithmetic Mean from the Upscale Formulae menu.

• 60. Click the Compute … button.

This formula takes the arithmetic mean for all values that lie inside a coarsened raster of the resulting IDF-file.

• 61. Observe the values of the TOP_LAYER3.IDF in relation to the scaled version TOP_
LAYER3_SCALED.IDF. Use Map Value ) and inspect the Additional Information in Map Info ).

Experiment with different Formulae for up- and downscaling.