How to manage custom coordinate systems in iTwin Capture Modeler Flex

 

Modeler Flex, iTwin Capture Engine and iTwin Capture cloud modeling Service CRS overview

About Gdal and PROJ

Modeler Flex, iTwin Capture Engine and iTwin Capture Cloud Modeling Service are all relying on GDAL 3.10 and PROJ 9.6.3 to handle coordinate system and transformations. Essentially, GDAL manages the coordinate system information for your data, while PROJ is the engine it uses to perform the mathematical transformations between different coordinate systems.

 

Architecture

Since Modeler Flex and iTwin Capture Engine are installed independently, each uses its own local set of CRS resources located in the installation directory under data/gdal. The cloud service also maintains its own installation. This leads to two key implications:

· To avoid inconsistencies, run Modeler Flex and iTwin Capture Engine on the same version

· Resources that are manually added to the installation of one product are not shared automatically.

 

Sharing resources through the CRSData folder

Most standard CRS resources are provided in the installation directories. However, users can add additional CRS definitions or transformation files—such as grids or override files—inside a CRSData folder created at the project level.

This folder is automatically shared across all tools working on the project, including:

· Modeler Flex

· iTwin Capture Engine

· iTwin Capture Cloud Modeling Service

 

To use this feature, create a folder named CRSData inside your project’s Project files directory. It may include items like:

· Custom CRS definitions

· Transformation grids (GTX, TIFF, ASCII, etc.)

· Additional resource files required by PROJ

 

Automating the creation of the CRSData folder

If you regularly rely on custom CRS resources, you can configure Modeler Flex to automatically include them in every new project.

By defining a global shared CRS resource folder in the Modeler Flex Settings, you can store all your custom files—such as TIF grids, GTX grids, CSV overrides, or custom PROJ database files—once and have them automatically copied into new projects.

To do so, open iTwin Capture Modeler Flex Settings and set up the directory that will be used as a template for all your new projects:

Whenever a new project is created, Modeler Flex copies the contents of this shared folder into the project’s CRSData directory, making the resources immediately available.

 

How to add custom CRS with WKT or PRJ files

You can create custom coordinate reference systems in three steps:

· Select the item Define new user system to start the creation of a new coordinate reference system.

· Click on Edit to define the new coordinate reference system.

· Enter a display name and the definition of the new user defined system.

· Alternatively, you can import the definition from a WKT, PRJ or DGN file using the load file button.

 

 

How to add a geoid model

If your custom CRS definition includes a vertical datum referencing a geoid model, you can simply add the geoid model file to the CRSData folder, and it will be used.

Note: in Modeler Flex, we are no longer limited to GTX file format only for the geoid model and the vertcs.override.csv method is not mandatory. It is still available if you wish to set up a specific vertical datum that is not available in the default package.

If you wish to set up a specific vertical datum that is missing from the existing Vertical Datum List, follow this step-by-step guide.

 

· In the data/gdal folder of the installation, locate the vertcs.override.csv file and copy it in your CRSData folder (see “Sharing resources through the CRSData folder” section above for more information).

· Open the CSV file and go to the first blank line (line 33 in the example below) and enter the description of the new vertical system, preceded by a #

· Access the EPSG registry using your web browser using the following url: EPSG Geodetic Parameter Dataset

· In the search box enter the country code for vertical datum you wish to search. In the case NZVD for "New Zealand vertical datum"

 

 

· The resulting search will find the nearest match to your request. In this case we select the most recent vertical option.

 

 

· The next page will display your vertical CRS in the top section

 

· Expand the Datum link to display the code for the vertical datum

 

· The resulting vertical datum code must be implemented in column C (DATUM_CODE). In this example "1169"

· The resulting name must be implemented in column D (DATUM_NAME). In this example "New Zealand vertical datum 2016"

· Columns E to I are filled with the same numbers as the other datum

· Column J (PARM_1_1) needs to be filled with the grid file name to be used.

· After running steps 6. to 11. of the procedure, the vertcs.override.csv file should be similar to the image below:

· Once this is all set, save the CSV file and add the related grid file reference in the CSV in the CRSData folder, alongside the vertcs.override.csv file.

· The new vertical CRS is now ready-to-use in iTwin Capture Modeler Flex and should be listed in the Vertical Datum List.