What does the survex/aven file give you, is the error there also
apparent?
What is your full thconfig file for generating the kml and aven .3d?
Dies the problem also exists when specifying this:
cs EPSG:4326
fix 0 19.009617 47.526453 262
Am 2021-02-19 11:25, schrieb Balambér Hakapesz:
If I were to enter the ellisoid height, the error of Proj4 would still
remain on the EOV projection.
I could work in a UTM coordinate system, but it would be much simpler
if Therion didn’t recalculate anything. (There is no height issue
between UTM and WGS84 because there is no conversion)
This error is only present in the national projections where Proj4
performs approximate calculations for the advantage of horizontal
coordinates and the disadvantage of height.
On Fri, Feb 19, 2021 at 11:25 AM Balambér Hakapesz
<holl.balaz...@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
<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?
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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.
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