Custom geoid model or post conversion

Emlid Flow & Emlid Flow 360 Coordinate Systems
1

Hi, i’m Alessio from Italy and i’m new in Emlid Comunity.
I’ve already bought an RS3, and while configuring it i’ve discovered that custom geoid model are not supported.
Specially here in italy, only EGM96 and 2008 are available as geoid model, which is not enough for any surveying purpose.

I need to use local geoid model, so my questions are:

  • will be available in next updates of Flow app, the capability to upload custom tiff geoids? honestly, i thought a piece of equipment like the RS3 were up to upoload custom geoid by default… i bought it without asking this.
  • Is it possible to save points in ellipsoidal heights and then post process with studio app?
  • if not, which workflow or app should i use to convert my points with a tiff geoid model or a Z shift if the survey area are small?
  • for my region, there’s an official geoid model, given for free by the administration. Is it possible to ask to upload to the database?
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3

Hi @alessio.bonfante,

Welcome to the community! Before I answer questions 3 and 4, could you please tell me where your projects are located, and what geoid model you need support for?

For Italy, we support the global heights listed above and the following local heights:

  • Genoa 1942(South Tirol) height
  • Italy ITG2009 height

At the moment we don’t support the upload of custom geoid models. But I’ve noted this as a feature request. I’ll let you know once we have updates on this.

Is it possible to save points in ellipsoidal heights and then post process with studio app?

It is not possible to transform coordinates in Emlid Studio. Emlid Studio is a software for post-processing data from GNSS receivers and RTK drones, not a coordinate transformation tool.

4

Hi Ruth, thank you for the reply.

Unlickily here in Italy we haven’t any “survey grade” geoid model for all the country for free, all the available geoid models, included the 2 you mentioned, are not for survey purpose but only for analysis, the mismatch from the “official” (and paid) geoid model are about from -0.5 to 0.5m from the “free” ones.

Our official geoid model, valid for survey purposes in all the country is ITALGEO2005. Which is sold by the “Italian Military Geographic Institute” (IGM), in grid files, where 1 grid (which is 300km2, not so big…) are sold for 110€ each… And for coordinate conversion with these grids they have their own closed software, ConVerGo, which can be used only with their grid files.
That’s why for Italy users is so important to have the custom geoid option.

What we have to do for any survey, is to buy the grid file of you survey area, create a geoid model and put the file on the GNSS (or do it in post processing with their software).
In my region, luckily, the geoid model is provided for free by the administration, my area is Trentino-Alto Adige:
Image of Trentino Alto Adige on map

https://www.provincia.tn.it/Documenti-e-dati/Documenti-di-supporto/Il-geoide-nelle-province-di-Trento-e-Bolzano-2003

Yesterday i’ve managed to create my custom geoid model from the “Grid 2003” file in the link above in Global Mapper, exported in .Bgd file, and used in Geographic Calculator for ellipsoidic to orthometric height conversion in a csv file, so post conversion solved.

Now in Global Mapper i’m able to export the conversion file in any format, so if you’re up for uploading this geoid model for this area on the library, i’m up to provide it in any format you need.

Thank you.

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5

I understand that uploading a custom geoid model can be useful for you. I’ve noted this as a feature request, along with ITALGEO2005 support for your region.

I can also suggest another tool for coordinate transformation. The PROJ library is also a useful tool for coordinate transformations. If you are familiar or comfortable working with the CLI, I believe the Vertical Grid Shift module would also be good as an alternative to convert the heights to Orthometric using your grid file.

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6

Thank you Ruth, i’ll try that for sure!

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7

You can calculate values, that’s what I do. You just need GIS software and the rasters of the different geoid heights which I downloaded from here Agisoft Metashape: Geoids