Setting the Coordinate System

Owned by Duy Pham
Last updated: 28 Oct, 2024
6 min read

Prior to EEMS 12, EEMS only supported two coordinate systems: the Cartesian and the UTM systems. 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 Figure 1.

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 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. Figure 3 shows a case of grid and model projection having the same projection (e.g., geographic). While 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.


Figure 2. Import girds.


Figure 3. Grid and Model Projection have the same projection.


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 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 Figure 6. We select the target projection from this form, as shown in 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.

Figure 5. Access Project Settings.


Figure 6. Access Project Settings.


Figure 7. 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 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 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 8). The parameters are characterized based on the UTM and WGS 84 systems.
    • Import button: Defines projection by importing coordinate system information from a *.prj file (Figure 9).
    • Download button: Defines projection by downloading coordinate system information with an EPSG Code (Figure 10).
  • No Projection: Selecting this means Cartesian projection will be applied to the entire project.

The Export button allows users to retrieve projection details and save them in a *.prj file.

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.

Figure 8. Define coordinate system with projection parameters based on UTM and WGS 84.


Figure 9. Define projection by importing a *.prj file.


Figure 10 shows a dialog that allows users to download projection information from the Internet using an EPSG code. EPSG codes for different 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 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.

Figure 11. Project Settings: General tab.



Figure 12. Project Settings: Default Precision tab.