# [Marble-devel] Reference system

marble_developer marble_developer marbledeveloper at gmail.com
Sun May 13 11:20:14 UTC 2012

```Hi,

I will try to explain it a bit better.

When the Earth turns the corresponding angle in each update of Marble
clock, the points added turn the same angle too, it's the normal behaviour
in Marble because the reference system rotates with the Earth globe.

In this case, a point that has the next values for lon, lat and alt doesn't
generate an orbit. lon, lat, alt = (0, 0, 20000 * 1000). The point is drawn
always in the same point of space.

I want that the points remain fixed in the space and they doesn't turn with
the Earth.

In this case a point that has the next values for lon, lat and alt
generates an orbit. lon, lat, alt = (0, 0, 20000 * 1000). The point is
drawn in differents points of space because the point drawn remain fixed in
space.

For example, we consider that the update interval of Marble clock is 10800
s, (10800 s is the time that the Earth use to turn 45º) and that a point
with values lon, lat, alt = 0,0, 20000 * 1000 is added in each update of
Marble clock. At first, when the time is 0 s, the point p is drawn in 0,0,
20000 * 1000, then, when the time is 10800 s, the point p is drawn in 0,0,
20000 * 1000 but the last point p' is in -45, 0, 20000 * 1000 respect the
new point p.

I have performed this behaviour by recalculating the new lon position in
every update but it's very slowly when the number of points is elevated.

How can I do this task in a better way? Is it possible to change the
reference system using in Marble?

Regards.

2012/5/7 marble_developer marble_developer <marbledeveloper at gmail.com>

> Hi all,
>
> Is it possible to change the reference system using in Marble?
> In affirmative case, how can I change it?
> I need to use an inertial reference system instead of fixed reference
> system.
>
> Best regards.
>
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