Pandora's box

[dr-ni]

we have now opened Pandora's box. Should we support other projections, too?

https://en.wikipedia.org/wiki/List_of_map_projections

[zvezdochiot]

Relax, @dr-ni .

We don't have a single projection algorithm.

B-L-H <-> X-Y-Z translation is a translation from one kind of 3D coordinates to another kind of 3D coordinates. 3D!!!

It's just that X-Y-Z depends only on the center point and three vectors, and B-L-H depends on the whole 3D figure - an ellipsoid. But both of these systems are 3D, without projections.

Dont worry, be happy.

[dr-ni]

yes, but this is only working for ellipsoid projection methods, isn't it?

[zvezdochiot]

Not, @dr-ni .

This works for ellipsoids. Without any projections.

[dr-ni]

yes but there are many many other methods (=projection methods whithout ellipsoid projections) so this is only! for ellipsoids

[zvezdochiot]

Not, @dr-ni .

We do not use any (ANI!) projections.

[dr-ni]

I know but what is with all those other stuff that is not based on ellipsoidal coordinate systems

[zvezdochiot]

@dr-ni say:

but what is with all those other stuff

• https://proj.org
• https://github.com/Geo-Linux-Calculations/geofindkey
• https://github.com/Geo-Linux-Calculations/gnumeric-ols/tree/master/spreadsheets/conformaltrans
• https://github.com/Geo-Linux-Calculations/gauss-kruger
• https://github.com/Geo-Linux-Calculations/geoconformimage
• https://github.com/ImageProcessing-ElectronicPublications/photoquick-examples/tree/main/plugins/transform/geometry

[dr-ni]

off course - this was what I was thinking about if we support ellipsoids we also should support any other common local/global coordinate transformation

[zvezdochiot]

@dr-ni say:

we also should support any other common local/global coordinate transformation

Not. I introduced the B-L-H <-> X-Y-Z transformation, only because the B-L-H representation is more common and this transformation is not projective.

See also Geomatics Guidance Note 7, part 2 Coordinate Conversions & Transformations including Formulas (version 57, September 2019) 373-07-02.pdf

[dr-ni]

nice paper :-) to avoid further missunderstanding - should we use instead of blh lat lon h

[zvezdochiot]

@dr-ni say:

instead of blh lat lon h

And what is the short entry? This one doesn't go anywhere.

• https://www.latlong.net/
• https://en.wikipedia.org/wiki/Geographic_coordinate_system

"The "latitude" (abbreviation: Lat., φ, or phi)"
"The "longitude" (abbreviation: Long., λ, or lambda)"

In Russia geodesic "latitude" - B, geodesic "longitude" - L.

[dr-ni]

in germany also b=Breite l=Länge h=Höhe maybe the russian was taking over the german but nowadys rather everywhere lat and lon are common I can later add this to the manual and we leave blh...

[dr-ni]

are spheres also working with helmeltrans

[dr-ni]

shall we add for all a separate file?

[zvezdochiot]

@dr-ni say:

are spheres also

Yes. They are sometimes used to machine spherical triangles. This is an approximation, but very good.

@dr-ni say:

shall we add for all a separate file?

Crazy?! Dirty repository! Who needs to create it himself. Just put this file in a "prominent place".

[dr-ni]

ok, so we add the file to the ellipsoids folder?

[zvezdochiot]

@dr-ni say:

ok, so we add the file to the ellipsoids folder?

Not. To the documentation. Next to README.md

PS: Crazy thought: Shouldn't we make a separate helmert3d-data, hang up a banner there about collecting transformation matrices? Such a warehouse "with the world by thread".

[dr-ni]

could be also possible. Do you mean the helmparms3d output format?

[zvezdochiot]

@dr-ni say:

Do you mean the helmparms3d output format?

Yes.

[dr-ni]

but has to be checked always if correct and no spam

[zvezdochiot]

@dr-ni say:

but has to be checked always if correct and no spam

Issues are always open. Kind people will tell you.

PS: I said that the idea is delusional.

[dr-ni]

ok can you open it? I'll add the file to the repo, anyway

[zvezdochiot]

@dr-ni say:

ok can you open it?

I am a disgusting "marketer". This business will not go with me in charge. Let's leave crazy ideas to posterity.

[dr-ni]

ok

[zvezdochiot]

Hi @dr-ni

See also https://github.com/SammyB428/GFC/blob/24aaf24c3145f46e62a4d48ce2c36c75e49c155a/GFC/CEarth.cpp#L827-L1003

[dr-ni]

updated

[dr-ni]

I'm asking myself if this upgrade is a reliable one?

many precisions are so unrealistic, for example WGS84: WGS_84 6378137.0 6356752.3142451793 0.0000000003 m precisions????!!! for example 1 Å = 100 pm = 0.1 nm = 10^{−10} m The Ångström is used in particular in crystallography and chemistry to be able to work with "simple" numerical values. 1 Å is the typical order of magnitude for atomic radii and distances between atoms in crystal structures and bond lengths in molecules. Even the moon forces the earth surface around ±50 cm

[zvezdochiot]

@dr-ni . The initial values are a and 1/f. I already wrote about this. The polar axis b is calculated b=a*(1-f). Number of characters for storage only f.