Prior to the EEMS 12, EEMS only supported two coordinate systems: the Cartesian coordinate system and the UTM systemsystems. The Cartesian coordinate system primarily allows for simulations that require X and Y coordinates of calculation grids with a designated unit in meters, while the UTM system enables processing data overlain on a specified UTM Zone. However, both systems exhibit limitations when working with model grids spanning multiple UTM zones.
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When we create a new model, we can set the projection to the EFDC model. Click the New Model button, and the Cartesian Grid Generator form will pop up. Next, click the Set button for the Model Projection, and the Coordinate System form will display. We will define the projection for the model on this form by selecting an option from the drop-down arrow, as shown in Setting the Coordinate System (EEMS12) Figure 1.
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Figure 1: . Set Model Projection.
For example, we select the Geographic (Longitude/Latitude) option, then click the OK button, and the Coordinate System form will close. If we want to create a new model from multiple grids with the same coordinate system, we can check the checkbox "Use the same projection for all grids". After selecting Model Projection, we can import a grid from a file by clicking the Import Grids button. The Import Grid form will then pop up; from this form, we select grid type and then select the grid file by clicking the browse button. If we want to import multiple grids at once, we can check the checkbox "Multiple Grid Files.", as shown in Setting the Coordinate System (EEMS12) Figure 2.
Click the OK button, the Import Grid form closes, the Coordinate System form will display again to remind the user. Notice that the projection information shown in this form can be different from the projection in the Model Projection we set previously, as it is based on projection information from the grid file. Setting the Coordinate System (EEMS12) Figure 3 shows a case of grid and model projection having the same projection (e.g., geographic). While Setting the Coordinate System (EEMS12) Figure 4 shows a case of grid and model projection having different projections, and in this case, when clicking the OK button, the projection in the Model Projection will be updated as the projection in the grid file.
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Figure 2: . Import girds.
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Figure 3: . Grid and Model Projection have the same projection.
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Figure 4: . Grid and Model Projection have different projections.
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Once a model run is created, EE still allows you to switch between the Geographic and UTM Zone coordinate systems. To do that, we go to the Model menu and select Project Settings or click the Project Settings button from the toolbar, as shown in Setting the Coordinate System (EEMS12) Figure 5. The Projection Settings form will pop up. Select the Coordinate Projection tab, then click the Change button. The Coordinate System form will be displayed as shown in Setting the Coordinate System (EEMS12) Figure 6. We select the target projection from this form, as shown in Setting the Coordinate System (EEMS12) Figure 7 and click the OK to close it. Notice that from now on, once we change the projection to the model, this change will affect the model output when we run it.
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Figure 5: . Access Project Settings.
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Figure 6: . Access Project Settings.
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Figure 7: Access Project Settings.
Besides the Coordinate Projection tab, the Project Settings form has General, and Default Precisions. General tab allows setting unit system for the model. While The default Precisions tab allows the precision of parameters in the model to be set as shown in
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Figure 8: Project Settings: General tab.
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Figure 9: Project Settings: Default Precision tab.
Click on the Coordinate Projection section, and the currently applied or selected coordinate system is immediately presented in the window. As noted in the Warning: EFDC+ supports only Universal Transverse Mercator (UTM) and Geographic Projections. Any changes made will alter the projection of the model grid permanently, thus affecting multiple modelling functionalities.
To change the CS, click the Change button in the Projection Settings form.
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. Access Project Settings.
There are five reference coordinate systems as below:
- Geographic (Longitude/Latitude): Selecting this applies the World Geodetic System (WGS) 1984 to the project.
- UTM, Northern Hemisphere: Selecting this applies the Universal Transverse Mercator (UTM) - Northern Hemisphere projection. A drop-down menu will be enabled for specifying the specification of UTM Zone (from 1 to 60).
- UTM, Southern Hemisphere: Selecting this applies the UTM – - Southern Hemisphere projection. Similar to the UTM, Northern Hemisphere, users need to select an a UTM Zone for this CS in the second drop-down menu.
- User Defined: Besides the predefined WGS 1984 geographic coordinate system and UTM projection, users can define their own UTM projection or import/download any projection for the current layer. Choosing this option enables the Define, Import, and Download
- Define button: Defines projection by configuring the map projection parameters (Figure 48). The parameters are characterized based on the UTM and WGS 84 systems.
- Import button: Defines projection by importing a CS coordinate system information from a *.prj file (Figure 59).
- Download button: Defines projection by downloading CS coordinate system information with an EPSG Code (Figure 610).
- No Projection: Selecting this means no Cartesian projection will be applied to the entire project.
With all CS options, the The Export button is always enabled, allowing allows users to retrieve projection details and save them in a *.prj file.
Once the desired projection is selected, click OK to apply changes to the project.
Figure 3: Coordinate System settings
Figure 4 Figure 8 shows a dialog that allows defining a UTM projection with some specific parameters. The scale factor of 0.9996 is applied for the zone width of 6° of longitude, and the scale factor of 0.9999 is applied for the zone width of 3°. The central meridian indicates the central meridian longitude of the zone. The latitude of the original is usually taken as zero, and the false easting is usually taken as 500 000 meters. The false northing is taken the zero value for the Northern Hemisphere and is taken the value of 10 000 000 meters for the Southern Hemisphere.
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Figure 8. Define coordinate system with projection parameters based on UTM and WGS 84.
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Figure 5: 9. Define projection by importing a *.prj file.
Figure 6 10 shows a dialog that allows users to download projection information from the Internet using an EPSG code. EPSG codes for different CSs coordinate systems can be found at https://epsg.io or https://spatialreference.org. The EPSG codes for the projection information for UTM zones have the form EPSG:326xx. For example, the EPSG code for UTM Zone 10 is EPSG:32610, so users can enter the value of 32610 into the search box to download its projection information.
Figure 6: 10. Define projection using EPSG Code.
Besides the Coordinate Projection tab, the Project Settings form has General, and Default Precisions. General tab allows setting unit system for the model. While The default Precisions tab allows the precision of parameters in the model to be set, as shown in Figure 8 and Figure 12.
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Figure 11. Project Settings: General tab.
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Figure 12. Project Settings: Default Precision tab.