[Therion] 3D model height

Fri Feb 19 20:18:16 CET 2021

Hi,

which version of Therion and Proj are you using? I get
19.00961002698361,47.52649340144701,262.00000000000000
in the kml export with the latest Therion and Proj 7.2.1

Best wishes
Martin

On Fri, Feb 19, 2021 at 11:25 AM Balambér Hakapesz <holl.balazs63 at gmail.com>
wrote:

> thconfig:
> #cs long-lat
>     #fix 0 19.009617 47.526453 262
>     cs EPSG:23700               # Hungarian EOV
>     fix 0 647151 242509 262
>
> kml:
> <LineString><coordinates>
> 19.00961011626948,47.52649337576407,291.08568208889801
>
> 291-262 = 29 m = 44m geoid height - 15m Proj4 error
>
>
>
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> On Fri, Feb 19, 2021 at 11:06 AM Benedikt Hallinger <beni at hallinger.org>
> wrote:
>
>> Isn't EGM84 the reference ellipsoid currently used by WGS84?
>> What you get with GPS is *not* sea level, but the altitude above that
>> reference geoid (which takes into account gravital anonalys).
>>
>> If you calibrate your barometric altimeter to the hieght given by a
>> height coordinate of WGS84 (like read from your car's navi at the
>> parking lot, or from a map calibrated to WGS84) then you should get
>> about the same altitude.
>> If you take the cave location from GPS and enter that coordinates into
>> the therion dataset wirh correct "cs" marking, the conversion should
>> yield the correct result.
>> If you take the altitude from a map (or an altimeter calibrated to that
>> map) in another coordinate system, you have to either apply an offset
>> manually, add an instrument correction factor in therion, or supply the
>> correct coordinate system (which then probalby demands conversion of the
>> lat/lon coordinates).
>>
>> If generating 3D surfce meshes, you also need to supply matching
>> coordinate systems data and/or specify the correct "cs" parameter.
>>
>> I think your problem comes from mixing coordinate systems in respect to
>> the height model, either at data input or when using the height mesh.
>>
>>
>> Am 2021-02-19 9:49, schrieb Balambér Hakapesz:
>> > 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?
>> >
>> >                [2]
>> >               Mentes a vírusoktól. www.avg.com [2]
>> >
>> > On Fri, Feb 19, 2021 at 9:18 AM Benedikt Hallinger
>> > <beni at 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] [1]
>> >>>
>> >>>
>> >>>
>> >>> Links:
>> >>> ------
>> >>> [1]
>> >>>
>> >>
>> >
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>> >
>> > Links:
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>> > [1] http://www.avg.com
>> > [2]
>> >
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