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Data compression

The numerical data obtained by iSALE are stored in a strongly compressed, flexible, and (nearly) lossless manner. The File I/O of iSALE, iSALEPlot, vimod and other tools is performed in a user-friendly way by a separate library, libjc. This library is developed with iSALE and vimod and is provided with iSALE.

Compression techniques

libjc contains a number of different compression techniques, namely:

JPEG/JPEG2000

The data is compressed in a (lossy) way by using the JPEG-standard (ISO/IEC 10918-1). The compressed data is sorted with a huffman-code for further reduction of the required disc-space.

GZIP

This technique uses a Lempel-Ziv-Storer-Szymanski algorithm for a lossless compression of the data. Again, the compressed data is sorted with a huffman-code for further reduction of the required disc-space.

GZIP with range-mapping (16-bit unsigned int GZIP)

This technique works like the GZIP-technique described above, except that each value is mapped from 32-bit-floating-point domain to a 16-bit unsigned int domain before compression. The width of the transformation domain is controlled by a quality-parameter q. q=50 means, only 50% of the 16-bits are used for mapping. The transformation procedure can be described by following formula:

Compression quality

Not every compression technique is lossless. The compression error is not only dependent on the chosen technique and the compression density (quality-factor q), but also on the nature of the given field. Here we present the results of some tests for the commonly used fields...

Results

XXX = no visible artifacts
XX = very small (negligible) artifacts
X = small, but visible artifacts
- = larger artifacts. A usage for post-processing is not recommended.

Bold entries note the default compression technique and density for the given field.

Field Abbreviation Compression density and technique
JPEG compression 16-bit-unsigned int GZIP
99 85 50 -100 -50 -25
Artificial viscosity (viscous pressure) PVb XXX XXX XX XXX XXX XXX
Damage Dam XXX XX XX XXX XXX XXX
Pressure Pre XXX XXX XX XXX XXX XXX
Temperature Tmp XXX XX X XXX XXX XXX
Yield strength Yld XXX XXX XX XXX XXX XXX
Strain rate dev. (2nd. inv.) Ert XX X - XXX XX XX
Vibration velocity Vib XXX XX X XXX XXX XXX
Density Den X - - XXX XXX XX
Static - Dynamic Yield strength YAc XXX XXX XX XXX XXX XXX
Vibrational pressure PVb XXX XXX XX XXX XXX XXX
Velocity VEL X - - XXX XX XX
Specific internal energy Sie XX X X XXX XXX XXX
Speed of sound Csn XXX XX X XXX XXX XXX
Shear modulus SMU XX X X XXX XXX XXX
Artificial viscosity Art XX X - XXX XXX XXX
Volumetric Strain VSt XX X - XXX XXX XXX
Distension Alp XXX XX X XXX XXX XXX

Pressure

Range: 0-2.77e11 Pa; Color range: 0-5.e9 Pa

Pre

Density

Range: 0-5900 kg/m^3; Color range: mean +/-15 kg/m^3

Den

Artificial viscosity (viscous pressure)

Art

Distension

distension

Speed of sound (3500 m/s ... 4500 m/s)

Csn

Damage

Dam

Strain rate (2nd invariant)

Ert

Vibrational pressure

Pvb

Specific internal energy

Sie

Shear modulus

SMU

Temperature (0 ... 1000 K)

Tmp

Vibration velocity (0 ... 20 m/s)

Vib

Volumetric strain (0.5 ... 0.25)

VSt

Velocity (X-component; +/- 50 m/s)

Vx

Static - Dynamic Yield strength (0 ... 0.5)

YAc

Yield strength (0 ... 2.25e+9 Pa)

Yld

Alp_1.25_1.33.png View - distension (56.6 KB) Dirk Elbeshausen, 10/20/2011 03:05 PM

pressure_5e9.png View - Pre (181 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

pvb_1.e8.png View - Pvb (65.6 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

sie_5e5_1e6.png View - Sie (69.9 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

smu_1.9e9_2.1e9.png View - SMU (112 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

Art_1e5_5e7.png View - Art (60.4 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

csnd_3500_4500.png View - Csn (46.4 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

damage_01.png View - Dam (227 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

density_1970_2000.png View - Den (126 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

temp_0_1000.png View - Tmp (118 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

erate_0.05.png View - Ert (257 KB) Dirk Elbeshausen, 10/20/2011 03:16 PM

vib_0_20.png View - Vib (103 KB) Dirk Elbeshausen, 10/20/2011 03:17 PM

VSt_m0.5_0.25.png View - VSt (101 KB) Dirk Elbeshausen, 10/20/2011 03:17 PM

vx_pm50.png View - Vx (107 KB) Dirk Elbeshausen, 10/20/2011 03:17 PM

yac_0.5.png View - YAc (41.1 KB) Dirk Elbeshausen, 10/20/2011 03:17 PM

yield_0_2.25e9.png View - Yld (145 KB) Dirk Elbeshausen, 10/20/2011 03:17 PM

uint16_transformation.png View (6.36 KB) Dirk Elbeshausen, 10/24/2012 12:32 PM