With the release of EEMS 12.0, it is possible to revise the coordinate system (CS) of working projects. This feature is useful when the projection of an imported project is not specified correctly, resulting in inaccurate visualization and spatial analysis of gridded data. To view and modify the currently applied coordinate system, go to Model in the main toolbar and select Project Settings option (Figure 1). The Project Settings window, which accommodates three sections General, Default Precisions and Coordinate Projection, appears as shown in Figure 2.
Figure 1: Project Settings option
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Prior to the EEMS 12, EEMS only supported two coordinate systems: the Cartesian coordinate system and the UTM system. 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.
EEMS 12 introduces the Geographic Coordinate System (GSC) to handle geographic data more accurately and efficiently. The GCS in EEMS 12 aims to:
(1) resolve existing limitations of the currently available reference systems of the Cartesian coordinate system and Universal Transverse Mercator (UTM) system and;
(2) facilitate data processing where GCS acts as a fundamental projection system.
The ability of the Geographic Coordinate System to define two-dimensional coordinates longitude and latitude based on the Earth’s surface not only preserves the accuracy of visualizations of data points under a single projection but also avoids spatial distortion of the model and data.
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).
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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).
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) shows a case of grid and model projection having the same projection (e.g., geographic). While Setting the Coordinate System (EEMS12) 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.
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). 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). We select the target projection from this form, as shown in Setting the Coordinate System (EEMS12) 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.
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