CGNS and elsA

Poinot Marc
DSNA/ELSA
poinot@onera.fr
http://elsa.onera.fr

Motivations

• CFD standard for data representation is required
  • We want to use a common data representation for interoperability
  • We want to ensure our data a long life format
• ONERA is a CFD expert
  • We are one of the aerospace main actors
  • We want to participate to a standard
    • Add our expertise
    • Be aware of what's going on
• Some customers are asking for CGNS
  • Common data representation at specification level
  • Interoperability for application framework

CGNS related developments

• elsA
  • Main I/O data representation
    • In-memory tree
      • Interoperability / Multi-processing
    • Disk tree
      • Validation resources
• pyCGNS
• A Python binding to CGNS
• Gluing language for application framework
  • e.g. translators to CGNS trees
    • From/To Tecplot and Aerospace actors data format
• Open source
  • http://elsa.onera.fr/CGNS/releases

An ISO Data Representation

Application side features/ concerns

• Top level side
  • Share application data
    • Semantics
    • Common names/structure
  • Self-described tree structure
  • ISO process
• Lower level side
  • Share physical data
  • Actual interoperability between applications
  • CAUTION: NO STANDARDIZATION PROCESS
• Missing Features
  • Protocol
    • No data lifecycle
    • No data ownership
  • Specific data / extensions
    • Guidelines for proprietary sub-tree
  • Parallel
    • Application side: uses in-memory representation?
  • Share / Transactionnal / Query
    • DBMS uses blobs at application level?
  • Other
    • Force an XML mapping

Architecture

pyCGNS Status

• v0.3
  • Binding
    • Full ADF wrapper
    • 60% MLL wrapper
    • 10% OOL layer
  • Python + Numerical Python
    • Standard package
    • Documentation + test suite
  • Tools
    • SIFT - SIDS instance description check
    • ParseTree - Tree dump/display as XML tree
    • StampNode - Add sub-nodes with specific stamps (date, ownership ...)
  • http://elsa.onera.fr/CGNS/releases
• v0.4 (1Q2002)
  • In-memory representation
    • Python/C/C++/Fortran in-memory tree sharing
  • Tools
    • SIFT - Generate data tree from SIDS instance description
• v1.0 (3Q2002)
  • Binding
    • Full MLL wrapper
    • Full OOL layer
  • Documentation
    • Features 100% documented + tutorial
    • Design partly documented
  • Test suite
    • Complete test suite for OOL/MLL/ADFF

Code example - pyCGNS

#!/usr/bin/env python
# CFD General Notation System - CGNS lib wrapper
# ONERA/DSNA/ELSA - poinot@onera.fr
# User's Guide to CGNS - C.L.Rumsey et al. examples translation
#
from CGNS      import midlevel
from CGNS.wrap import *
from Numeric   import *
#
# open CGNS file for read-only
file=pyCGNS('grid.cgns',midlevel.MODE_READ)
index_base=1
index_zone=1
index_flow=1
isize=file.zoneread(index_base,index_zone)[3]
irmin=[1,1,1]
irmax=[isize[0],isize[1],isize[2]]
(loc,name)=file.solinfo(index_base,index_zone,index_flow)
if (loc != midlevel.Vertex):
  print "Error, GridLocation must be Vertex! Currently:",
  print midlevel.GridLocation[loc]
# read flow solution
r=file.fieldread(index_base,index_zone,index_flow,'Density',midlevel.RealSingle,irmin,irmax)
p=file.fieldread(index_base,index_zone,index_flow,'Pressure',midlevel.RealSingle,irmin,irmax)
# close CGNS file
del file
print "Successfully read flow solution from file 'grid.cgns'"
print "For example, r,p(21,17,9)=",r[20,16,8],p[20,16,8]
print "Program successful... ending now"