Lionel RUIZ

Olivier NIVOIX
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Lhoumeau Sky System
Lhoumeau Sky System - mode truncated  


With a FullHD videoprojector (1920x1080) and a LSS bloc, it's possible to increase the picture resolution in an efficient manner.

Advantage Drawbacks
Resolution (1400 to 1600 frame) Loss the northern horizon
sligntly brighter picture oriented projection

Part of the lost picture is proportional to the gain in resolution, since according to the north-south meridian, the number of pixels will always be limited to 1080. Then, we get situations similar to those obtained with a spherical mirror system (P.Bourke process), but with a quality of projection and resolution constant from center to edges. 

Lost Horizon 

So, the size of lost picture on the northern horizon will be

Hlost = 180 *[ 1 – (1080/resolution)]
Resolution East / West North horizon lost
1200 18° 
1400 41°
1600 58,5°

Testing and using...

For the first measure, we can use a pattern (click on picture to download).

To increase the field of pixels, reduce the zoom. In the installation of Yves Lhoumeau, the circle 1080p is obtained at maximum zoom position.

To adjust the picture in Truncated mode:

Reduce the zoom (to the minimum)

Change the inclination of the beamer (rear pads)


The field in truncated mode depends of the optical combination (type of Bloc / type of beamer). Depending on the combining, the limit will be 1200p or 1600p

Stellarium360 adaptation for truncated mode

It can easily be configurated with the software.

First, you have to edit the distortion.dat file located here:


It contains as follows:

# This file contains fisheye distortion correction parameters 

# and truncated mode configuration for Stellarium360.
# On the DESKTOP build, lens 1 is always used.
# Each distortion definition begins with a lens, height, pconfig line where:
#   lens = lens number
#   height = window height in pixels, or 0 to match any height
#   pconfig = projection configuration:
#      0 = truncated (or default configuration when truncation isn't an option)
#      1 = lens at dome center
#      2 = lens below dome center (such as for projection angles much under 180 degrees)    
# Following this is an optional viewport line, of the form:
# If these are between 0 and 1, they are interpreted as fractions of the screen width,
# otherwise as pixel values.  CENTER_Y is measured up from the bottom of the screen.
# Following this are distortion correction lines of two types:
#   L = lens distortion
#   G = geometry (projector placement) distortion
# Each type has two subtypes (as separate lines)
#   P = project function parameters
#   U = unproject function parameters
# parameters are:
#   a, b, c, limit, fudge_factor
# where for projection (unit circle):
#  if (f < limit ) {
#  f = a*f + b*f*f + c*f*f*f;
# } else {
#  f = f + fudge_factor;
# }
# (see src/fisheye_projector.cpp for implementation details)

### Default lens, any resolution, no distortion, allows truncated mode

lens 1 height 0 pconfig 0
viewport 960 800 800
LP 1.0 0.0 0.0 1.0 0.0
LU 1.0 0.0 0.0 1.0 0.0

lens 1 height 0 pconfig 1

LP 1.0 0.0 0.0 1.0 0.0
LU 1.0 0.0 0.0 1.0 0.0

lens 1 height 0 pconfig 2

LP 1.0 0.0 0.0 1.0 0.0
LU 1.0 0.0 0.0 1.0 0.0

### END OF FILE ###

The line "viewport 960 800 800" means that the resolution is 1920 and the center is located at X=960 (=1920/2) and Y=280 (=1080-800 in FullHD 1080p). The radius here is R=800.

To activate the truncated mode, you'll have to go to the Configuration Menu (M = Spanner) and go to the sub-menu 8.8 Projection configuration and select "Truncated projection" with the "Return" and "arrows" keys.

Adapting movies for truncated mode 

If you are working with domemasters directly, I suggest to use XnView that permits to modify your images one by one in a batch mode to resize and crop to the desired values.

With videos directly, I suggest using VirtualDub. More limited but very powerful if you master how works the "filters" section of the software.
© 2016 LSS Group - Yves LHOUMEAU & Lionel RUIZ