enhancement - azimuthal grid + equatorial / galactic grid (low)

[johndpope]

I will endeavor to build an armillary sphere that can augment this app / it could be another section in app - will need these will map to earth celestial sphere. shots taken from

I appreciate that the screen shots below are a divergence to this project -
and intention is to illustrate how other apps are showing these things.
These views don't need to be implemented in app.
but the grid lines / drawings would be cool to illustrate in scenekit.
eg. where are the galactic poles

https://github.com/Stellarium/stellarium

[johndpope]

once we can work out one - should all fall into place.
Of course - this won't look like this in augmented solar system.
just 3d view wrapped around the earth sphere.

[johndpope]

I wonder how this would look in 3d.

[johndpope]

from cosmographia 3d scene is available for this grid https://github.com/johndpope/cosmographia

[johndpope]

http://worldwidetelescope.org/webclient/

https://github.com/jzuhone/openwwt-windows-client/blob/master/WWTCore/WWTCore/Constants.cs

EquatorialGrid, EquatorialGridText, GalacticGrid, GalacticGridText, EclipticGrid

[johndpope]

https://github.com/cardinot/celestia/blob/bc9403d55fa592a7fc9a7a694aec783e9f62a37f/celestia/src/celengine/skygrid.cpp

// The maximum number of parallels or meridians that will be visible
const double MAX_VISIBLE_ARCS = 10.0;

// Number of line segments used to approximate one arc of the celestial sphere
const int ARC_SUBDIVISIONS = 100;

// Size of the cross indicating the north and south poles
const double POLAR_CROSS_SIZE = 0.01;

// Grid line spacing tables
static const int MSEC = 1;
static const int SEC = 1000;
static const int MIN = 60 * SEC;
static const int DEG = 60 * MIN;
static const int HR  = 60 * MIN;

static const int HOUR_MIN_SEC_TOTAL = 24 * HR;
static const int DEG_MIN_SEC_TOTAL  = 180 * DEG;

static const int HOUR_MIN_SEC_SPACING[] =
{
    2*HR,
    1*HR,
    30*MIN,
    15*MIN,
    10*MIN,
    5*MIN,
    3*MIN,
    2*MIN,
    1*MIN,
    30*SEC,
    15*SEC,
    10*SEC,
    5*SEC,
    3*SEC,
    2*SEC,
    1*SEC,
    500*MSEC,
    200*MSEC,
    100*MSEC
};

static const int DEG_MIN_SEC_SPACING[]  =
{
    30*DEG,
    15*DEG,
    10*DEG,
    5*DEG,
    3*DEG,
    2*DEG,
    1*DEG,
    30*MIN,
    15*MIN,
    10*MIN,
    5*MIN,
    3*MIN,
    2*MIN,
    1*MIN,
    30*SEC,
    15*SEC,
    10*SEC,
    5*SEC,
    3*SEC,
    2*SEC,
    1*SEC,
    500*MSEC,
    200*MSEC,
    100*MSEC
};