Goole Earth and the free software equivalent - Earth 3D

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Goole Earth and the free software equivalent - Earth 3D

Petter Reinholdtsen

I guess some of you have seen Google Earth,
<URL:http://earth.google.com/>.  But did you see the free software
"equivalen", Earth 3D, <URL:http://earth3d.org/>?  It need more data,
but the software to handle it is already in place.


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Re: Goole Earth and the free software equivalent - Earth 3D

Lars Aronsson
Petter Reinholdtsen wrote:
> I guess some of you have seen Google Earth,
> <URL:http://earth.google.com/>.  But did you see the free software
> "equivalen", Earth 3D, <URL:http://earth3d.org/>?  It need more data,
> but the software to handle it is already in place.

I guess our friends in London have enough to worry about already,
and my thoughts are with them.

One thing that irritates me with Google Maps and their satellite
images is the stupid map projection, where the vertical grid lines
(longitudes) run in parallel, making the north pole not a point
but a horizontal line as long as the equator.  This kind of
projection is not uncommon in U.S. printed maps, where it makes
many state borders conveniently appear as straight lines, but
totally unheard of in northern Europe.  Northern Greenland in this
kind of projection becomes very wide, as wide as South America.

There are three versions of such map projections: (1) one where
the land area is kept constant by shortening the vertical scale as
much as the horizontal scale is expanded (Greenland becomes wide
and short), (2) another where the vertical scale is kept constant,
and (3) a third one where angles are kept constant by increasing
the vertical scale as much as the horizontal scale is expanded
(where Greenland becomes very wide and very long).  Google seems
to be using (2) for its satellite images and (3) for its maps.  
This is easily spotted if you flip between maps and satellite
images of Greenland,
http://maps.google.com/maps?ll=75,-50&spn=30,30

On that *map*, Sweden looks "normal" (angles preserved), but much
enlarged compared to Africa, while Svalbard is the size of
Germany.

The same problems will happen to OSM and other projects, once we
start to map Greenland and Svalbard.

The right solution to these problems is to view the world not as a
flat map, but as a 3D projection of the globe from some point in
space.  So why doesn't Google Maps do this already?

The answer is that Google Maps are built up from small tiles that
are cached, both on the server and in the browser.  You can break
a flat and square map into tiles, but you cannot do this with a 3d
view of a globe.  In Google Maps and satellite images, you can
click north-east-south-west and be back at the same square you
started from.  You cannot do that on a globe.  On the contrary, if
you start from the North pole and walk 1 mile south, 1 mile east,
1 mile north, you will be back at the North pole.

The challenge is to build a map web application that can use the
economic benefits of caching, while not perverting the map
projection.  Caching means the map fragments computed for one user
should be reused for the next user, or for the same user the next
time the same part of the map is shown.

For an application that runs on a single user's computer (such as
Google Earth, it's an .exe for MS Windows), the computing power
might be enough to ignore caching.  But that would not be a web
application, where one user can post a link (look at this place!)
to another user.


--
  Lars Aronsson ([hidden email])
  Aronsson Datateknik - http://aronsson.se

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Re: Goole Earth and the free software equivalent - Earth 3D

Petter Reinholdtsen
In reply to this post by Petter Reinholdtsen

[Petter Reinholdtsen]
> But did you see the free software "equivalen", Earth 3D,
> <URL:http://earth3d.org/>?  It need more data, but the software to
> handle it is already in place.

I made a debian package for it.  Fetch it from
<URL:http://developer.skolelinux.no/~pere/debian/earth3d_1.0.2-1_i386.deb>.

I do not get it to show the textures properly, but I suspect it is
because my HW OpenGL support isn't great.


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Re: Goole Earth and the free software equivalent - Earth 3D

Chris Holmes-2
In reply to this post by Petter Reinholdtsen
Quoting [hidden email]:

> I guess some of you have seen Google Earth,
> <URL:http://earth.google.com/>.  But did you see the free software
> "equivalen", Earth 3D, <URL:http://earth3d.org/>?  It need more data,
> but the software to handle it is already in place.

There's also worldwind: http://worldwind.arc.nasa.gov/
It's open source, though unfortunately written in .NET, not the most
open source friendly language.  There seems to be a pretty decent
community around it though, for awhile they had much better global
coverage than google earth, but am not sure if that's still the case.
The thing I really like about it is that it supports WMS, an open
standard for overlaying mapping data, instead of reinventing the wheel
with KML.


Chris

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Re: Goole Earth and the free software equivalent - Earth 3D

Petter Reinholdtsen

[Chris Holmes]
> There's also worldwind: http://worldwind.arc.nasa.gov/
> It's open source, though unfortunately written in .NET, not the most
> open source friendly language.

Does it work on Linux?  I only have linux machines available.

> There seems to be a pretty decent community around it though, for
> awhile they had much better global coverage than google earth, but
> am not sure if that's still the case.  The thing I really like about
> it is that it supports WMS, an open standard for overlaying mapping
> data, instead of reinventing the wheel with KML.

Isn't earth3d supporting WMS?  I thought it did, but did not really
check.


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