Product(s):	WaterGEMS, WaterCAD, HAMMER, SewerGEMS, SewerCAD, StormCAD, CivilStorm
Version(s):	24.00.02.XX and later
Area:	Layout and Data input

Background

A coordinate system defines how to view spatial data on a flat viewing surface (such as a map or screen). This article explains how to work with coordinate systems (regardless of the platform), to set the coordinate system of your hydraulic model and external data such as background maps and data imported through ModelBuilder and Loadbuilder.

Coordinate System features supported per version

Version 24.00.02.XX and 24.00.03.XX support setting the coordinate system of the model and of the background map (road or aerial). Meaning, in these versions, setting the coordinate system only influences the ability to align the model with a Background Map, and Shapefile Exports (PRJ file). This enables you to more easily align a model without having to manually align three points.
Version 26.00.00.XXX and higher also support setting the coordinate system of external data imported through ModelBuilder, LoadBuilder, Terrain Extractor (Trex), Thiessen Polygon, and other background layer types. Additionally, these versions support reprojection of the model by changing the model's coordinate system.

Setting the Model Coordinate System

To establish the coordinate system of your hydraulic model, open the Options (in the Standalone version this is located under File > Options > Hydraulic Model), then click "Set Coordinate System".

In the dialog that appears, you can browse or search for your coordinate system using the Search tab. For example if you know the EPSG code you can search for that as well.

Click the Add to Favorites button at the bottom to add the selected coordinate system to the "Favorites" section (see top of list), as a convenient shortcut to re-select in the future (for example for other models).

Note that when you select a coordinate system a map view is shown on the right side, to help you by clarifying the region covered by that coordinate system.

Important: the coordinate system assigned to the hydraulic model must be a projected coordinate system, since the model elements must use X and Y coordinates, rather than degrees of latitude/longitude (used in Geographic Coordinate Systems). Starting with version 2026, external data (via ModelBuilder, LoadBuilder, etc) can use a geographic coordinate system (see this article), but when assigning a Coordinate System to the hydraulic model, it must be a projected coordinate system. Therefore no items will appear in the folders within Geographic Coordinate Systems.

Changing the Model Coordinate System

If you need to change the Coordinate System after you initially set it, you can do so from Options > Hydraulic Model. Click the Change button and select the new Coordinate System.

In version 26.00.00.XXX and higher, a prompt will ask if you want to reproject the data. This option should be used if the model's original coordinate system was correctly selected, but you want to change it to a new coordinate system and transform the model coordinates. If you simply need to correct the model's coordinate system because the wrong one was initially selected, choose the other option from the prompt, to simply change the designated coordinate system, without transforming/converting the model coordinates.

Using Coordinate Systems in Background Maps (Standalone)

Note: version 2024 and earlier used Bing Maps for the background map service, and version 2026 and later use Google Maps (and is referred to as simply "Background Map")

When adding a background map (road or aerial) from the Background Layers manager, if the model coordinate system is not yet set, you can click "Set coordinate system" to set it (see above).

If the model coordinate system is already established, the background map will automatically align with the model.

If you select the Manual option for the Map Alignment, you can still enter the 1 or 3 Control Point options to add a Background Map.

If you have set the Coordinate System for your Background Map and wish to revert back to the 3-point manual alignment method, you must clear the hydraulic model’s set Coordinate System. From File > Options > Hydraulic Model. Click the Clear button. Click OK, go back to the Background Map properties and select “Manual” under Map Alignment.

Using Coordinate Systems with other Background Layers (Standalone)

Shapefiles and DXF background layers support Coordinate Systems in version 2026 and higher and will automatically reproject to align with the hydraulic model's coordinate system, if different (and if the model coordinate system is specified).

For a shapefile background - its .PRJ file must be present in order for the OpenFlows application to detect its coordinate system. If the .prj is not present, you can optionally specify the coordinate system of the shapefile using the "..." button (see below) and it will reproject automatically to align with the model's coordinate system (if different). Otherwise if a coordinate system is not specified for the shapefile background, it is assumed to be the same as the hydraulic model.

For a DXF background, you can optionally specify the coordinate system using the "..." button and it will reproject automatically to align with the model's coordinate system (if different). Otherwise if a coordinate system is not specified for the DXF background, it is assumed to be the same as the hydraulic model.

Using Coordinate Systems with ModelBuilder, Trex and Terrain Models

ModelBuilder, LoadBuilder, Trex and Terrain Models support Coordinate Systems in version 2026 and higher and will automatically reproject to align with the hydraulic model's coordinate system, if different.

When importing shapefiles with ModelBuilder, Terrain Extractor or the Terrain Models manager (Storm and Sewer products only), if the external file's coordinate system data is present (for example the .PRJ file for a shapefile), it will recognize the coordinate system and automatically reproject the data to the model's coordinate system if they are different. This ensures the imported data aligns with the model data and is imported to the right location.

If the shapefile .PRJ file is not present, or if you are importing another file type that does not have coordinate system data, you can optionally specify (assign) the coordinate system using the "..." button and the imported data's X and Y coordinate information will reproject automatically to align with the model's coordinate system (if different). Otherwise if a coordinate system is not specified, it is assumed to be the same as the hydraulic model.

ModelBuilder:

Terrain Extractor (Trex):

(manually selected)

Terrain Models (storm and sewer products only):

(manually selected)

Coordinate Systems and LoadBuilder

When using shapefiles with LoadBuilder to import loading information in version 2026 and higher:

If the shapefile's coordinate system is defined in a .PRJ file - LoadBuilder will automatically reproject the shapefile data into the model's current coordinate system (if different).

If the shapefile's .PRJ file is missing or if the model coordinate system is not defined - it behaves as it did in earlier versions and proceeds under the assumption that the shapefile is in the same coordinate system as the model and does not attempt to do any reprojection.

Note: if the shapefile is in a different coordinate system but does not have a .prj file, and you need to specify the shapefile's coordinate system, ensure the model's coordinate system is set, then use the flextable shapefile export mentioned below to generate a .PRJ file that can be used with the shapefile you want to import with LoadBuilder (copy the .prj file and rename the base file name to match the shapefile you are trying to use).

Coordinate Systems and Shapefile Export

Starting with version 24.00.02.2X, shapefiles exported from element flextables generate a .PRJ file containing the coordinate system, if a coordinate system has been specified in the model. This enables you to align your exported model elements in other outside applications. This also applies to exported decoration lines (dashed lines).

Coordinate Systems and Thiessen Polygon

Starting with version 2026, the Thiessen Polygon tool will generate a .PRJ file with the model's coordinate system.

Coordinate Systems and 2D Modeling (SewerGEMS and CivilStorm)

Starting with version 2026 of SewerGEMS and CivilStorm, the 2D adjustment layers used in the Surface Definitions manager for 2D modeling now supports coordinate systems to automatically align (and reproject, if needed) the shapefile with the hydraulic model.

Working with coordinate systems in the OpenFlows Products