Resources for geoid models

I have not worked with geoid models and need to obtain the orthometric height from the ellipsoidal height provided by reach RS2. I am also working in Asia where it is difficult to locate the geoid models in some countries. Can soomeone point me to some resources on obtaining, interpreting and applying the geoid models to my ellipsoidal data?

Hi @itenviro,

It is possible to get orthometric heights with Reach RS2 using our ReachView 3 app. You can choose desired vertical datum while creating a new project. If you’d like to work with any particular geoid, you can tell it to me, and I’ll check if ReachView 3 already supports it.

UPD: Fixed terminology a bit just not to get confused

Thanks. I had looked at the data but found no model for Lao. I have a lao geoid model file in bin format, but not sure what to do with it. As well, I am not sure of the accuracy or provenance of the model. I know Reachview3 offers EGM96 which I think is a global model geoid and was considering that as a last resort. But really, I need a better understanding of how to practically use geoid models, their different formats, software etc

Hi @itenviro,

May I ask you to share the vertical datum name so that I can double-check if it is supported in the app? If you know its EPSG code, it would be of help as well.

Geoid model files can’t be uploaded directly to the ReachView 3 app. However, if you’d like to work with a vertical datum that the app doesn’t currently support, we can consider adding it after your request.

Sorry for the delay. I am working in Lao PDR (Laos). Technical sector here is not very developed and with covid, foreign tech firms have largely left. Otherwise I might be able to find out the geoid model commonly used here. So I am on my own at the moment. I am an engineer, not a surveyor and to be honest, I am not exactly sure what to look for and I havent found a comprehensive reference on the practical application of the geoid model to survey data.
From what I understand the model comprises a map grid say in tif format overlain on the region of interest with a vertical adjustment indicated for each cell. I would imagine that the vertical adjustment could be interpolated from values in adjoining cells. Depending on the elevation at the point of interest, there might also be a horizontal adjustment. If that is correct I am looking for a tif with grid references and a programme to perform the interpolations.
A search at Georepository brings up a couple of 3d references to Lao, latest 2007 but dont see a model to download.
Any help pointing me to some learning material and geoid model sources would be much appreciated.

Hi @itenviro,

Let me elaborate on geoids and grids a bit to make it clearer.

A geoid is a level surface that can be a part of a vertical datum. The vertical datum should also include an initial point (usually a coastal tide gauge) so that the geoid model will be referenced to the ground.

Vertical datums usually have EPSG codes. If your vertical datum has such a code, it is most likely already supported in ReachView 3, and you can find it by this code. If not, we can consider adding it in the future. However, we need additional data from you to accomplish it. For example, the vertical datum name, geoid file, etc.

For plane coordinates, you should choose a coordinate system that may have an EPSG code as well. In some countries, you need to apply shifts to get the correct coordinates of the points. The grid file is needed to determine the shift for each point.

A grid may be a part of a coordinate system. If the coordinate system has an EPSG code, the grid and the coordinate system will come together in the ReachView 3 app. If the coordinate system doesn’t have an EPSG code, the government usually provides all necessary data and software for the conversion.

In case you can provide us with the coordinate system name or the grid file, it will help to consider the possibility of adding the coordinate system to ReachView 3.

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