Very rarely can anyone work at ellipsoidal heights. In local coordinate systems, it only makes sense for upper geodetic calculations. Only for GPS measurements we get an ellipsoidal altitude, even there the devices can immediately calculate the altitude of the EGM96 model with an altitude above sea level (with a few meters error which is not significant compared to the 15m altitude error of handheld GPS).
Proj4 calculates the horizontal coordinates well, but there is a serious error in the height coordinates (for special national projections (http://www.agt.bme.hu/gis/workshop4/eloadasok/proj_poszter_3d.pdf)), so it would be better if not we would count on it but leave the altitude unchanged.

Could it be an option not to change the height with Therion?

On Fri, Feb 19, 2021 at 9:18 AM Benedikt Hallinger <beni@hallinger.org> wrote:

Hi there,
if you measure the altitude with a barometric device, you do not get the
altitude above the ellipsoid. You have to account for that at the input
of your data.

With the "cs" command you define your input data to be in a specific
coordinate system, and also your altitude has to be given in that
system. If you just put the barometric altitude there (which you usually
did calibrate to a map, didn't you?) you have to transform the altitude
manually if the reference altitude differs.

Am 2021-02-19 8:44, schrieb Balambér Hakapesz:
> Hi!
>
> When generating 3D models, Proj4 transforms between different
> coordinate systems.
> This also transforms the ellipsoidal altitude, but the data always
> refer to altitude above sea level and should not be changed.
> The finished models do not fit the topography, you have to cheat with
> the height to be good.
>
> Balázs Holl.
>
> [1]
> Mentes a vírusoktól. www.avg.com [1]
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