Shrinking VT resolution in polar latitudes
Posted: 08.03.2006, 22:40
Hi all,
this is a first attempt to reduce the reported rendering problems of Fightspit's MONSTER VT tile set of the 128K Earth based on Blue Marble 2nd Generation.
Here is Chris' expert evaluation:
One (partial) workaround is what I have just completed
OK here we go:
I wrote a neat zsh-script that automatically reduces the (horizontal) tile sizes in polar latitudes (see below).
The script should also work under CYGWIN/Windows but needs the zsh (because of its math-module).
The script also needs the 'convert' command line application of ImageMagick that exists for all OS's.
I have optimized the horizontal sizes of Fightspit's 128k Earth tiles (2k x 2k) with this script. The savings are substantial:
++++++++++++++++++
4.8GB ==> 3.7 GB !!
++++++++++++++++++
While the previously reported rendering errors (black tiles) in levels 4,5 have become much more rare, they still occur as well as occasional crashes. The latter clearly indicate a bug in the code, since crashes should NEVER occur
. There is NO visible reduction in image quality!
Calling the script without parameters (or with --help) produces this output:
--------------------------------------------------------------------
Usage: texopt [--help | <level> <tile size> <tile format>]
The shell script 'texopt' is a tool for Celestia > 1.3.0
that optimizes virtual texture tile resolution as function of latitude.
The script requires the standard square tiles tx_i_j
with size <tile size> [px] equal to a power of two,
in a specified format, <tile format> = png, tga, jpg,....
Besides Linux/Unix, the script also runs in a current Cygwin installation
under Windows, ( http://www.cygwin.com ). The zsh is needed!
The script assumes that a recent version (>= 6.1. 8 ) of the ImageMagick package
( http://www.ImageMagick.org ) is installed (either under Unix/Linux or Windows).
The utility 'convert' of that package is used.
Author: Dr. Fridger Schrempp, fridger.schrempp@desy.de
Version: 1.00, 06/03/06
---------------------------------------------------------------------
After typing e.g. in the level 4 directory:
the typical output is
----------------------------------------------------
In case the exact reduced tile size is less than 20% above the next /lower/ power of two, the latter is
given preference over upward rounding (see 2nd entry in the table above). This amounts to a slight effective loss of resolution for the respective row of tiles, but to a much higher saving of space!
Oh I forgot:
=======
The script creates a new subdirectory 'opt' in the levelx directory and outputs a complete new set of optimized tiles in there. This happens either by an appropriate horizontal size reduction or just by copying in case no size reduction is due.
Bye Fridger
Here is the script for people to play....
this is a first attempt to reduce the reported rendering problems of Fightspit's MONSTER VT tile set of the 128K Earth based on Blue Marble 2nd Generation.
Here is Chris' expert evaluation:
Chris wrote:
This seems to be due to Celestia not managing the texture memory well
enough. The 2k x 2k PNG tiles are very large, each requiring 8MB (2k * 2k
* 4 bytes per pixel) of texture memory. Near the poles, more texture tiles
will be simultaneously visible--just enable wireframe mode and observe the
high density of triangles near planet poles to get an idea of why this is
so. If you're very near a pole and close enough to the Earth so that level
4 tiles are used, at least 32 8MB tiles will need to be made resident
simultaneously. That's as much total video memory as there is on the
card--you just can't have that many textures in use.
One (partial) workaround is what I have just completed
Chris wrote:
Reduce the resolution of tiles nearer the poles. The horizontal
resolution of the tiles near the poles can be reduced. The circumference
at a latitude is cos(latitude) * equatorial circumference. At level 5, a
planet is sectioned into 32 latitude bands, each of 5.625 degrees; thus
the horizontal resolution of the northern and southernmost tiles could
reasonably reduced to cos(90 - 5.625) * equatorial tile resolution. That's
~200 pixels for 2k tiles (which should be rounded up to the nearest power
of two, 256.) Less dramatic savings could be achieved elsewhere. Note that
the vertical resolution of the tiles should be constant.
OK here we go:
I wrote a neat zsh-script that automatically reduces the (horizontal) tile sizes in polar latitudes (see below).
The script should also work under CYGWIN/Windows but needs the zsh (because of its math-module).
The script also needs the 'convert' command line application of ImageMagick that exists for all OS's.
I have optimized the horizontal sizes of Fightspit's 128k Earth tiles (2k x 2k) with this script. The savings are substantial:
++++++++++++++++++
4.8GB ==> 3.7 GB !!
++++++++++++++++++
While the previously reported rendering errors (black tiles) in levels 4,5 have become much more rare, they still occur as well as occasional crashes. The latter clearly indicate a bug in the code, since crashes should NEVER occur
. There is NO visible reduction in image quality!
Calling the script without parameters (or with --help) produces this output:
--------------------------------------------------------------------
Usage: texopt [--help | <level> <tile size> <tile format>]
The shell script 'texopt' is a tool for Celestia > 1.3.0
that optimizes virtual texture tile resolution as function of latitude.
The script requires the standard square tiles tx_i_j
with size <tile size> [px] equal to a power of two,
in a specified format, <tile format> = png, tga, jpg,....
Besides Linux/Unix, the script also runs in a current Cygwin installation
under Windows, ( http://www.cygwin.com ). The zsh is needed!
The script assumes that a recent version (>= 6.1. 8 ) of the ImageMagick package
( http://www.ImageMagick.org ) is installed (either under Unix/Linux or Windows).
The utility 'convert' of that package is used.
Author: Dr. Fridger Schrempp, fridger.schrempp@desy.de
Version: 1.00, 06/03/06
---------------------------------------------------------------------
After typing e.g. in the level 4 directory:
Code: Select all
> texopt 4 2048 png
the typical output is
----------------------------------------------------
Code: Select all
Level = 4
Tilesize = 2048
Number of tiles = 512
Image format of tiles: png
Latitude Exact multiple 2^n rounding
[degs] of 128 pix
----------------------------------------
+-84.375 1.5682738989 2
+-73.125 4.6445545474 4
+-61.875 7.5423475641 8
+-50.625 10.1502923852 16
+-39.375 12.3681671508 16
+-28.125 14.1107401749 16
+-16.875 15.3110453515 16
+-5.6249 15.9229556245 16
In case the exact reduced tile size is less than 20% above the next /lower/ power of two, the latter is
given preference over upward rounding (see 2nd entry in the table above). This amounts to a slight effective loss of resolution for the respective row of tiles, but to a much higher saving of space!
Oh I forgot:
=======
The script creates a new subdirectory 'opt' in the levelx directory and outputs a complete new set of optimized tiles in there. This happens either by an appropriate horizontal size reduction or just by copying in case no size reduction is due.
Bye Fridger
Here is the script for people to play....
Code: Select all
-----------------------------texopt-------------------------------------------
#! /usr/bin/zsh
if [ $# -lt 3 -o "$1" = "--help" ]; then
echo
echo 'Usage: texopt [--help | <level> <tile size> <tile format>]'
echo
echo
echo The shell script \'texopt\' is a tool for Celestia \> 1.3.0
echo that optimizes virtual texture tile resolution as function of latitude.
echo
echo The script requires the standard square tiles tx_i_j
echo with size \<tile size\> \[px\] equal to a power of two,
echo in a specified format, \<tile format\> = png, tga, jpg,....
echo
echo Besides Linux/Unix, the script also runs in a current Cygwin \
installation
echo under Windows, \( http://www.cygwin.com \). The zsh is needed!
echo
echo The script assumes that a recent version \(\>= 6.1.8\) of the ImageMagick package
echo \( http://www.ImageMagick.org \) is installed \
\(either under Unix/Linux or Windows\).
echo The utility \'convert\' of that package is used.
echo
echo Author: Dr. Fridger Schrempp, fridger.schrempp@desy.de
echo Version: 1.00, 06/03/06
echo
else
zmodload zsh/mathfunc
level=$1
tilesize=$2
tileformat="$3"
(( p2 = 2**level ))
echo
echo "Level = " $level
echo "Tilesize = " $tilesize
echo "Number of tiles =" $(( 2 * p2 * p2 ))
echo "Image format of tiles:" $tileformat
echo
echo "Latitude " " Exact multiple " "2^n rounding"
echo " [degs] " " of 128 pix "
echo "----------------------------------------"
mkdir opt
cd opt
j=0
pi=3.1415927
(( latband = pi/p2 ))
while (( j <= p2/2 - 1 )); do
i=0
# calculate the latitude reduction in the /middle/ of the tile
(( redsize = cos(0.5 * pi - (j + 0.5) * latband) * tilesize/128.0 ))
#
# Returns the next power of 2 if redsize isn't 2^n
# or returns redsize if redsize is 2^n
#
power2=1
while (( power2 < redsize )); do
(( power2 <<= 1 ))
done
#
# if redsize exceeds the smaller power of two by less than 20%
# the latter is used.
#
if [ "$(( (redsize - power2 / 2) / redsize ))" -lt 0.2 ]; then
(( power2 = power2 / 2 ))
fi
echo "+-"$(( 180*( 0.5 - (j + 0.5) * latband/pi ) )) " "$redsize " " $power2
(( redsize = 128 * power2 ))
(( jm = p2 - 1 - j ))
if [ "$redsize" -lt "$tilesize" ]; then
while (( i <= 2 * p2 - 1 )); do
convert ../tx_"$i"_"$j".$tileformat -resize "$redsize"x"$tilesize!" tx_"$i"_"$j".$tileformat
convert ../tx_"$i"_"$jm".$tileformat -resize "$redsize"x"$tilesize!" tx_"$i"_"$jm".$tileformat
(( i++ ))
done
else
while (( i <= 2 * p2 - 1 )); do
cp ../tx_"$i"_"$j".$tileformat tx_"$i"_"$j".$tileformat
cp ../tx_"$i"_"$jm".$tileformat tx_"$i"_"$jm".$tileformat
(( i++ ))
done
fi
(( j++ ))
done
fi
Encore bravo, Jeam