Projections & Coordinate Systems

Owned by Duy Pham
Last updated: 22 Oct, 2024 by Kester Scandrett
6 min read

There are three places to access the projection settings of Grid+, as described below.

  1. Access from the toolbar button, as shown in Projections & Coordinate Systems#Figure 1.
  2. Access from the File menu, as shown in Projections & Coordinate Systems#Figure 2.
  3. Access from the Tools menu, as shown in Projections & Coordinate Systems#Figure 3.

When the Projection Settings is selected, the Projection Settings form will appear as shown in Figure 4. As mentioned in the information box below, The user is not able to change the coordinate system from this form as Grid+ chooses the WGS84 geographic coordinate system as a default setting. It means that when we create any files from Grid+ and then export them to external files, their coordinates are in Latitude and Longitude. Figure 5 shows coordinates of a spline file when opening with the Notepad editor as an example. The first line of the file provides information on the coordinate system.

By default Grid+1.2 always works with the Geographic Coordinate System (GCS). This means that its coordinates are longitude and latitude.

While the projection settings cannot be changed, Grid+ allows the user to convert from the geographic coordinate system for each file layer in the Layer Control panel to the Universal Transverse Mercator (UTM). The user must define the correct UTM zone number for the latitude and longitude location. For example, we have made a grid by using Grid+ for the Caloosahatchee River in Florida, USA. As we have defined it, this river is located in the northern hemisphere UTM zone 17. We now want to convert the grid from the geographic coordinate system to the UTM zone.

To do this, select the grid layer from the Layer Control panel, then Right-mouse click (RMC), select Properties as shown in Projections & Coordinate Systems#Figure 6. After that Grid Settings form will appear. Select Coordinate System tab, as shown in Projections & Coordinate Systems#Figure 7, and then click the Convert button. The form for the Coordinate System will pop up, as shown in Projections & Coordinate Systems#Figure 8. Now, we need to define the correct target coordinate system to which we want to convert. In this case, we select UTM zone 17 in the northern hemisphere,Ā  then click OK button. Next, click OK button in the form of Projections & Coordinate Systems#Figure 7 to close it. Coordinate system conversion is now complete.


Figure 1. Access projection settings from a toolbar button.


Figure 2. Access projection settings from File menu.


Figure 3. Access projection settings from Tools menu.


Figure 4. Projection Settings form.


Figure 5. Open a generated file by Grid+ with the Notepad editor.



Figure 6. Select the Properties option of a layer in Layer Control (e.g., Grid layer).


Figure 7. Grid Settings: Coordinate System tab.


Figure 8. Convert Coordinate System.


In this step, we will export the grid to an external grid file. Select the grid layer from the Layer Control panel, then RMC, select Export/Export Grid as shown in Projections & Coordinate Systems#Figure 9. After that Export Grid form will appear, enter a file name and click Save button, as shown in Projections & Coordinate Systems#Figure 10.

Opening the grid file with the Notepad editor, we can see that the file contains UTM zone number information (e.g., 17 means that UTM zone 17, in the northern hemisphere) and coordinates values are Easting and Northing in units of meters, as shown in Projections & Coordinate Systems#Figure 11. The UTM zone number will be negative for the southern hemisphere, as shown in Projections & Coordinate Systems#Figure 12.

For a file that is converted from geographic coordinates to UTM zone by Grid+, do we need to define a coordinate system when opening it by Grid+? The answer is no because Grid+ will get projection information in header lines from the file and locate it in the correct place.

Figure 9. Export the Grid layer to an external file (1).


Figure 10. Export the Grid layer to an external file (2).


Figure 11. Exported grid in the northern hemisphere.

Figure 12. Exported grid in the southern hemisphere.

When we import a grid that is not the native grid of Grid+ into Grid+ (this grid file does not have projection information in the file), for example, RGF grid (*.grd), we need to define projection for it by selecting right-mouse click on the grid layer in the Layer Control and then selecting Properties, the Grid Settings form will pop up. We select Coordinate System tab, click the Define button. Then, we should select the proper spatial reference, either geographic or UTM coordinate system. Then click the OK button to finish the projection defining step. Next, right-mouse click on that grid layer in the Layer Control, then select Zoom to Layer option, the grid will be located in the right place.

Updating Overlay Files

In another case, when we open an overlay file generated by a CVLGrid such as *.P2D, or from third-party software, for example, a shoreline *.LDB (Delft3D LDB format), we will need to define the coordinate system..

In this case, we consider the shoreline as an overlay file so that we will click the Import button from the toolbar, then select Import Overlay as shown in Projections & Coordinate Systems#Figure 13. The Import Overlay Layer form will pop up. Select the file and click Open button, as shown in Projections & Coordinate Systems#Figure 14. As a result, a new shoreline layer is added to the Layer Control panel, as shown in Projections & Coordinate Systems#Figure 15. However, when we RMC on that layer and select Zoom to Layer option, it is not located in the place we expected. This is because the file does not contain the coordinate system information, so Grid+ does not know where it should be located. This means we must make the shoreline located in the right places in the online background map.Ā 

To correctly configure the shoreline location, we must define the correct projection (coordinate system) to the file. RMC on that layer and then select Properties option. TheĀ Overlay Properties form will pop up. Select the Coordinate System tab and click theĀ Define button as shown in Figure 16. The Coordinate System form will appear, as shown in Figure 17, and we will select the correct projection from this form. The projection should be known by the user. In this case, we select UTM zone 17, northern hemisphere. After that, click OK button. This form will close and go back to the form in Projections & Coordinate Systems#Figure 16. Next, click OK button to close the form. The process for defining the coordinate system is completed. RMC on the shoreline layer and select Zoom to Layer,Ā and it will be located in the correct location, as shown in Projections & Coordinate Systems#Figure 18.


Figure 13. Import third-party files with Grid+.


Figure 14. Select the file to import.


Figure 15. New shoreline layer added to Layer Control.



Figure 16. Coordinate System: Define.


Figure 17. Coordinate System: Define.



Figure 18. Shoreline located in the correct place after defining a coordinate system.