Adding Turkey TG20 geoid model to pix4d software


Our country’s Official Institute of Geodesy offers a 5’x5’ geoid model free of charge. Can we add this data to the database of pix4d products (mapper, matic, survey etc.)?



Hi Kasim,

Thank you for this request and the link to the relevant authority. Before we can include a geoid into our software, we first need to add the geoid model to the PROJ library. Inclusion is especially beneficial for the local authority, making this geoid available to a broader audience, as any tools or software using this library will have free access to the geoid. There are several requirements for acceptance listed below. This requires the assistance of the local authority to complete this step, but we will also be available to help however we can.

Requirements for inclusion:

  1. Geoid grid files. These files define the geoid model and are generally in the ASCII file format.

  2. The vertical coordinate reference system needs to be defined in EPSG. If the vertical coordinate reference system is not defined, the local authority will need to submit a request for its addition.

  3. New grids/geoids are accepted into the package if released under a license compatible with the Open Source Definition. The source of the grid is clearly stated and verifiable. Suitable licenses include:

  • Public domain
  • X/MIT
  • BSD 2/3/4 clause
  • CC0
  • CC-BY (v3.0 or later)
  • CC-BY-SA (v3.0 or later)

These licenses can be found through this link:

The open-source initiative has a very helpful FAQ that can help answer many common questions and misconceptions surrounding this process. While it can sound daunting, it is not difficult and is a better practice for the local authority.

  1. The license and geoid files need to be publicly displayed. The swisstopo website can serve as an example. At the bottom of the page, you will see a link to the Creative Commons CCO license and the geoid files. The public should be able to access this information, preferably without needing to register or sign in.

  1. In they say “If the grid is not yet registered in the EPSG database, you are strongly encouraged to engage with EPSG to register it. This will make its addition to PROJ and its later maintenance much easier. EPSG Dataset Change Request Help explains the procedure to follow to submit a change request to EPSG.” Please, this is something to transmit to the authority.

EPSG Dataset Change Request Help

Some examples from other countries are: “ETRS89 to Alicante height” (Spain) “ETRS89 to ODN height” (UK) “ETRS89 to NAP height” (The Netherlands) “NAD83(2011) to NAVD88 height” (USA, using GEOID18)

ETRS89 to Alicante height (1)

I hope this information proves helpful. Do you know anyone with the local authority to see about getting compliance for PROJ inclusion? If not, I can reach out to them. We have just found the process can be much smoother with a known contact.