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 <b...@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
> > <b...@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]
> >>>
> >>
> >
> http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
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> >> Therion mailing list
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> >> https://mailman.speleo.sk/listinfo/therion
> >
> >
> > Links:
> > ------
> > [1] http://www.avg.com
> > [2]
> >
> http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail
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