Fwd: Rotation of projection plane

[Jasem Mutlaq]

---------- Forwarded message ----------
From: "Artem Fedoskin" <afedoskin3 at gmail.com>
Date: Feb 15, 2017 2:00 PM
Subject: Fwd: Rotation of projection plane
To: "Jasem Mutlaq" <mutlaqja at ikarustech.com>
Cc:

Dear contributors and users of KStars,

At the moment I am working on "Automatic mode" for KStars Lite (that is, a
mode in which Sky Map is controlled by accelerometer and magnetometer of
your smartphone). I built Java backend for getting data from sensors data
but I have the following problem:

Imagine you a pointing to the Moon (a center of your screen is pointing to
the Moon). If you will rotate the screen of you phone around the Moon
without rotating the whole Sky Map the image will stay same. The goal is to
rotate the Sky Map so that your smartphone still points to the Moon but all
other parts of Sky Map will change according to rotation (imagine of your
smartphone as a window to the sky or simply check Google Skymap in Play
Store).

Right now I am getting the following when I rotate SkyMapLite according to
roll data from sensors. As you can see, current projection system is not
rotated therefore objects that should be drawn are hidden and ground
polygon isn't drawn correctly ( I guess in case of ground I will simply
disable its rectangle form and draw the whole thing in Automatic mode).

http://imgur.com/a/QCFxc

[image: Inline image 1]

What I have already tried is the following - http://math.stackexchange.com/
questions/270194/how-to-find-the-vertices-angle-after-rotation I am
calculating new coordinates according to formulas in Projector::
checkVisibility( SkyPoint *p ) but it doesn't work. Any ideas how should I
calculate new points?

You can check "Automatic mode" by building KStars Lite using the following
script https://github.com/knro/build_kstarslite/.

My another small question is - should we set slewing to false in "Automatic
mode"? With slewing set to "on" it will be just like controlling Sky Map
with touch screen and won't be that spectacular as a lot of objects are
hidden. But on the other hand it will make automatic mode much smoother on
low-end devices.

Regards, Artem
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