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4th CGC Workshop on Computational Geometry. Geometry at Work: Open Issues Encountered in Real Applications using BRL-CAD TM. Michael John Muuss The U. S. Army Research Laboratory. Why We Model. Storytellers communicate feelings to people. “Skin-deep” models are fine for movies. - PowerPoint PPT Presentation
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16-October-1999 1
Geometry at Work:Open Issues Encountered in
Real Applications using BRL-CADTM
Michael John MuussThe U. S. Army Research Laboratory
4th CGC Workshop onComputational Geometry
16-October-1999 2
Why We Model
• Storytellers communicate feelings to people.+ “Skin-deep” models are fine for movies.
• We are predicting or matching physical phenomena:+ Energy levels received by a sensor.+ Damage statistics of live-fire tests.
16-October-1999 3
Modeling is OnlyOne Part of the Process
Experiment
IntegratedSurvivability/Lethality
Analysis ProductsAnalyze
Model
Today’s topic is modeling and simulation.
16-October-1999 4
Modeling Means Different Things...
• Goal: Re-creating the real-world in simulation:+ Re-creating individual laboratory tests.
• Science & Engineering community starts here.+ Re-creating real proving grounds.+ Re-creating training centers and actual exercises.+ Re-creating combat locations and scenarios.
• Training community & wargamers start here.
16-October-1999 5
The Simulation Challenge
16-October-1999 6
Meeting the Simulation Challenge
• Engineering-level geometric detail.• Physics-based simulation.• Realistic 3-D atmosphere, ground, and sea models.• Fast: Hardware-in-the-loop, man-in-the-loop.
+ Real-time, near-real-time, Web, and offline.• Common geometry.• Common software.• Massively parallel processing.
16-October-1999 7
Two Types of Simulation
• Image Generation
• “If you can’t see it, you can’t shoot it.”
• Vulnerability/Lethality Analysis
• “Will the bullet bounce off?”
16-October-1999 8
OUTLINE
• I. BRL-CADTM and Targets• II. Shooting Bullets• III. Making Pictures
16-October-1999 9
I. BRL-CADTM and Targets
16-October-1999 10
BRL-CADTM Primitive Solids
sphere spheroid ellipsoid right circularcylinder
right ellipticalcylinder
truncated rightcircular cone
truncatedgeneral cone
truncatedelliptical cone
topo. cubic6-hedron
edge-contractedtopo. cubic 6-hedron right triangular
prismquadrilateral
pyramidtetrahedron
intersectionof halfspaces
torus
elliptical-ringtorus right parabolic
cylinderright hyperbolic
cylinderelliptical
paraboloidelliptical
hyperboloid waterline-basedpolyhedron
Path and bend convex hullof two spheres
extrudedbit map
revolvedplane curve
extrudedplane curve
halfspacevoxel data
general polyhedron
trimmed NURBS
16-October-1999 11
BRL-CAD Primitive Solids
16-October-1999 12
wedge
cylinder
block
(wedge block) cylinder
wedge block cylinder
block (wedge cylinder)
CSG Boolean Operations
16-October-1999 13
Hierarchical Database Organization
tank
turrethull suspension
gunturret_armor turret_interior
crew
breech gun_tube bore_evacuator
cylinder_1.s cylinder_2.s cylinder_3.s
Directed
Acyclic
Graph
16-October-1999 14
A Medium-Resolution BRL-CAD Database
16-October-1999 15
Corps Command Post
16-October-1999 16
Library of Existing BRL-CAD™ Geometry
16-October-1999 17
One Geometry,Multiple Uses
• To compute ballistic penetration & vulnerability:+ Need 3-D solid geometry and material information.
• The same targets are also useful for:+ Signatures: Radar, MMW, IR, X-ray, etc.+ Smoke & Obscurants simulation.+ Chem./Bio agent infiltration.+ Electro-Magnetic Interference.
• BRL-CADTM is the basis for all our simulations.
16-October-1999 18
Ray Tracing
Startingpoint
distance,obliquity,normal,
curvature,etc.
16-October-1999 19
Evaluating Boolean Expressions in CSG
A
B
C
100 110 010 011 010
A B – C
ABC:
Segments:
16-October-1999 20
II. Shooting Bullets
16-October-1999 21
physics,penetration models, ...
Vulnerability/LethalityAnalysis Process
Initialthreat/targetconditions
Componentdamage
Systemcapability
Systemutility
engineering,criticality analysis, ...
operations research,missions, scenarios, ...
Level 1
Level 2
Level 3
Level 4
16-October-1999 22
Computing Component Damage(Level 1 to Level 2 Mapping)
CSG model of vehicle
Damage Results
Specification ofmunition performance
Shotlines representingPenetrator+spall paths
Vulnerability model
Ray tracerSpall
16-October-1999 23
Ray-tracing Through a Target
glacisarmor
armor-piercingrounds
HEround
firewall
enginestarter
transmissionsump
fanrear
armor
16-October-1999 24
0 900 mm
Perforationinto internal volume
Residual penetrationinside internal volume
Penetration Results
16-October-1999 25
Behind-Armor Debris(Flash X-Ray)
16-October-1999 26
Spall: a Secondary Damage Mechanism
• Experimental Data:
+ Perpendicular jet.
• Simulation Results:
+ Oblique impact.
Thousands of fragments to track!
Each generates another ray.
Behind-Armor-Debris is BAD.
16-October-1999 27
Main Armament Fault Tree
Main Armament Subsystem
Fault Trees map component failure
to subsystem capability.
Mapping from Damageto Capability (L2->L3)
Subsystems per vehicle: 50-100
16-October-1999 28
Is a Ray aGood Approximation
for a Fragment?• Sensor pixel. 0.01mm diameter -- OK.• Rifle bullet. 5.56mm diameter -- Maybe.
• Tank bullet. + 30-120mm diameter -- No.
16-October-1999 29
In General: No!
• Real particles have non-zero cross-section.+ A 0-thickness ray is not the best approximation.
• A real fragment will hit wires that the ray will miss.• Most damage is done by spall cloud.
+ Has a large total surface area.+ We sample density distribution with 1000’s of rays.+ This greatly under-samples the target geometry.
16-October-1999 30
Beam or Cone Tracing?
• Obvious solution: + Model particle path as a cylindrical beam.+ Model light ray as a cone.
• Solve cylinder-vs-object or cone-vs-object intersections.+ Such intersections yield complex volumes.
16-October-1999 31
A Ray Slipping ThroughComplex Geometry
Object on Centerline
Ray
16-October-1999 32
A Beam throughComplex Geometry
r > 0
Object on Centerline
16-October-1999 33
Objects in the Beam
Object on Centerline
16-October-1999 34
A Simplified Viewof the Relationships
Object on Centerline
But it isn’t this simple!
16-October-1999 35
Relations Along a Ray
appears-before
entirely-precedes occults
16-October-1999 36
Difficulties withCone-tracing
• Intersection with more general solids is expensive.+ E.g. height field, or t-NURBS.
• Representation of the results is difficult.+ No exact representation of the volume.
• At best, result could be some kind of B-rep.+ No convenient abstraction of volumetric result.
• Partially ordered sets!• Utilizing the results is difficult.
+ How to compute ricochet -vs- penetration?
16-October-1999 37
A Plea!
• Are there any good representations for these intersection volumes?
• Are there any good abstractions for these intersection volumes?
16-October-1999 38
Our Short-Term Strategy
• Fire additional rays distributed around main ray.+ Tightly coupled with space partitioning, for high
performance.+ User-selected patterns.
• Peripheral rays intersected only when main ray does not intersect geometry.
• Heuristics for choosing a single interval as “most representative” of material in that region.
• Reduces missing small objects in beam path.
16-October-1999 39
III. Making Pictures
16-October-1999 40
What is PST?
• PST = PTN and SWISS, Together!+ PTN = Paint-the-Night
• Real-time polygon rendering• From CECOM/NVESD
+ SWISS = Synthetic Wide-band Imaging Spectra-photometer and Environmental Simulation• Ray-traced BRL-CAD™ CSG geometry• From ARL/SLAD
16-October-1999 41
Application of PST
• The image generator is just one component of a larger simulation. E.g. MFS3, or missile simulation.
PSTPST ATR6 DoF
Flight DynamicsImages
Motion_t
Full Environment SimulationFull Platform Simulation
or HWIL
Control Decisions
Full Platform Simulation
or HWIL
16-October-1999 42
Paint-the-Night
• 8-12 micron IR image generator.• SGI Performer based.• Uses outboard image processor for sensor effects.• A large highly tuned monolithic application
+ With exceptionally high performance.+ Highest polygon rates seen on a real application.
• Individually drawn trees (2 perpendicular polygons)• Individually drawn boulders.
16-October-1999 43
SWISS
• A physics-based synthetic wide-band imaging spectrophotometer+ A camera-like sensor + Looks at any frequency of energy.
• A set of physics-based virtual worlds for it to look at:+ Atmosphere, clouds, smoke, targets, trees,
vegetation, high-resolution terrain.• A dynamic world; everything moves & changes.
16-October-1999 44
A Grand-ChallengeComputing Problem
• Real targets, enormous scene complexity, > 10Km2.• Physics-based hyper-spectral image generation.• Nano-atmospherics, smoke, and obscurants.• Ray-traced image generation, exact CSG geometry.
+ Near-real-time (6fps).• Fully scalable algorithms.• Network distributed MIMD parallel HPC.• Image delivery to desktop via ATM networks.
16-October-1999 45
Ray-Tracing forImage Synthesis
16-October-1999 46
Advantages of a Ray-Tracing SIG
• Allows reflection, refraction:
+ Windshields, glints.
+ Branch reflections, 3-5 µm.
• Atmospheric attenuation, scattering.
+ Individual path integrals.
• Accurate shadows:
+ Haze, clouds, smoke.
• Multiple light sources:
+ Sunlight, flare, spotlight.
2nd-Generation FLIR image, 8-12 µm
(Downsampled to 1/4 NTSC)
16-October-1999 47
CSG Rendering Advantages
• Ray-traced CSG is free from limitations of hardware polygon rendering:+ No approximate polygonal geometry.
• No seams, exact curvatures.+ Exact profile edges. Important for ATR!+ No level-of-detail switching, no “popping”.+ Full temperature range in Kelvins, not 0-255.+ Unlimited spectral resolution, not just 3 channels.
16-October-1999 48
Cruise Missile Shadow
Ridge Profile
Missile Shadow
Terrain Quantization
16-October-1999 49
Target Geometry Complexity
• Need at least 1cm resolvable features on targets.
16-October-1999 50
Complex Geometry Today
• < 1cm target features.• 1m terrain fence-post spacing• Three-dimensional trees:
+ Leaves.+ Bark.
• Procedural grass, other ground-cover.
• Boulders, other clutter.Current
Developmental
16-October-1999 51
Procedural Grass
16-October-1999 52
Ray-Traced Atmosphere
• Propagation easy in vacuum!
• Modeling four effects:
+ Absorption
+ Emission
+ In-scatter
+ Out-scatter
• Computer can’t do integrals.
+ Repeated summation
+ Discretized atmosphere
16-October-1999 53
The Blue Hills of Fort Hunter-Liggett
16-October-1999 54
Hyper-Spectral: The Power of a Single Pixel
16-October-1999 55
Open Issue:Representing Reflectance
• For each material used in the virtual world, need bi-directional reflectance distribution function (BRDF),
• Need BRDF as function of wavelength, too!• Seek a representation of this data which is:
+ Compact to store.+ Easy to locate important lobes.
16-October-1999 56
V/L Server
Terrain
Thermal Models
VehicleDynamics
Paint-the-NightPolygon Renderer
BRL-CAD™Ray Tracer
::
HLA
with
enh
ance
men
ts
Backplane Philosophy
• Standardized Slots (Interface).• Location independent
+ Except for performance.
Paint-the-NightPolygon Renderer
16-October-1999 57
PST Implementation Goals
• To have a software backplane:+ Allowing each function to run as separate process.+ Allowing easy reconfiguration.+ Allowing independent software development.+ Using common geometry throughout.+ Multiple Synthetic Image Generator (SIG) types.
• Keep simulation details out of the SIGs.
16-October-1999 58
Required Backplane Features
• Event Services+ Implement with HLA interactions.
• Query/Response Services+ HLA interactions with custom routing space.
• Continuous/Bulk Data+ Custom Distributed Shared Memory software.
• Auto-broadcast, optional subscriber notification.• Notification, subscriber polls for data update.
16-October-1999 59
PST Simulation with RT
RT
SIG
RT
SIG
DB
Solar
Load
Gen
Atmosphere
Ground Therm
Tree Therm
Target Therm
Monitor
Met
Input
Transducers
Entity
ControllersWorld
Simulations
Sensor
SimulationOutput
Transducers
ToD
MFS3
HW
FlyBox
Mapper
Mapper
MapperVehicle
Controller
Vehicle
Dynamics
MODSAF
I/F
Vehicle
Dynamics
Sensor
Controller
MODSAF
Intersect
Process
Magic
Carpet RTSYNC
Temp.
16-October-1999 60
PST Simulation with PTN
PTN
SIG
Data-cube
DB
Solar
Load
Gen
Atmosphere
Ground Therm
Tree Therm
Target Therm
Monitor
MetTextures
Input
Transducers
Entity
ControllersWorld
Simulations
Sensor
Simulation Output
Transducers
ToD
MFS3
HW
FlyBox
Mapper
Mapper
MapperVehicle
Controller
Vehicle
Dynamics
MODSAF
I/F
Vehicle
Dynamics
Sensor
Controller
MODSAF
Intersect
Process
Magic
Carpet
16-October-1999 61
Independent Time Scales
• Image generators need to run fast:+ 30 Hz for humans.+ 6 Hz is fastest acquisition rate of ATRs.+ 800 Hz for non-imaging sensors (Stinger rosette).
• Physics-based simulations can run slower:+ 90 sec/update for thermal & atmosphere models.
• Transient effects need to be added as a delta:+ Leaf flutter, explosions, smoke details.
16-October-1999 62
Hardware Environment
• Multiple CPUs per cabinet.• Multiple cabinets linked via OC-3 or OC-12 ATM.
+ Geographically distributed (Belvoir, APG, Knox).• Multi-vendor system, e.g.:
+ Cray vector machine for thermal mesh solution.+ SGI Origin 2000 for parallel ray-tracing.+ SGI Infinite Reality for polygon rendering.
• 100-200 processors participating.
16-October-1999 63
Ft. Knox Applicationof PST
• 1 RT SIG, 3 SGI SIGs, soldiers-in-the-loop.
DTV
DTV
DTV
DTV
PSTPST
RT
PTN
PTN
PTN
DREN
ATM
AT
M to D
-2 Video
Digital V
ideo to AT
M
Mapper
Mapper
Mapper
Mapper
DREN ATM
16-October-1999 64
The Ft. Knox Experiments
• One SWISS ray-traced image display.
+ For most sensitive tests.
• Multiple PTN polygon image displays.
+ Esp. to test teamwork.
• All in one shared environment: terrain, air:
+ Craters, smoke, haze…
+ Multiple players, threats.
• Ray-tracer in Maryland
+ >200 cpu Origin-2000
• Environment Sim in MD.
+ Cray T916, 16 cpus.
• Three PTN SIGs in VA.
+ Infinite Reality
• Man-in-the-Loop in KY.
+ Digital Image Display
OC-3 ATM
OC-3 ATM
16-October-1999 65
Real-Time Performance!
• Geometry has Spatial Coherence.+ We exploit that!
• A lot of the performance of our ray-tracer comes from extensive use of space partitioning.+ Muuss NUBSP tree, a flavor of Kd tree.
• Cost of ray/model intersection is proportional to local geometric complexity, not O(n). (good property)
16-October-1999 66
Data Structures versus The Hardware
• Kd tree • Memory Hierarchy
Processor
L1 Cache
L2 Cache
Translation Look-aside Buffer (TLB)
Memory Bus / Network
Bank Arbitration
RAM
Retrieve:
axis,
value,
pointer
O(3 log n)
trips to RAM
16-October-1999 67
Walking a Binary Tree
• Speed of walking a binary tree is limited by raw access time to main memory.+ No pipelining, no unrolling, no pre-fetch.+ Caches don’t help much.
• Binary tree’s memory-wait penalty accounts for 65% of runtime on R8000. Worse on Origin2000.
• Can’t live without space partitioning, alternative is massive O(n) search, >100X slower.
16-October-1999 68
A Plea to the Research Community
• Develop “cache friendly” algorithms & data structures• Universities teach that memory access time is uniform
across address space, not time varying. E.g. Knuth.+ Valid for old non-cached non-paged machines, 70s+ DEC PDP-11/45, Cray-X/MP.
• DEC VAX-11/780 added TLB, circa 1980.+ Extra trips to memory on TLB miss.
• And then came the caches…
16-October-1999 69
Example of an Alternative: NUGrid
• Non-uniform 3-dimensional grid of leaf nodes.• Index in several dozen instructions, 3D DDA.• Few loads required to get to intended volume.
+ Can double overall speed on large models.• M. Gigante, “Accelerated Ray Tracing using Non-
Uniform Grids”, Proceedings of Ausgraph ’90.
O(0) extra
memory
references
16-October-1999 70
Some Final Thoughts
• ARL really cares about Geometry and Algorithms.+ We appreciate your research!
• When you write an ARO grant proposal,+ Feel free to suggest me as a reviewer.+ Or Paul Tanenbaum.
16-October-1999 71
Acknowledgements
• Lee Butler (environment: smoke, grass, …)• Paul Tanenbaum (PO sets)• Max Lorenzo, CECOM
+ His team of SAIC contractors• Chris Johnson, Paladin Software• DoD HPCMO• OSD ATR• VPG
16-October-1999 72
Who is this MUUSS Fellow, Anyway?
Mike Muuss
Señor Scientist
U.S. Army Research Laboratory
APG, MD 21005-5068 U.S.A.
http://ftp.arl.mil/~mike/
16-October-1999 73
Peer Assessment of BRL-CAD
“an effective constructive solid modeling capability with highly efficient ray tracing”
“a computer-aided engineering (CAE) system, uniquely suited to survivability and lethality applications … in which physics-based simulations can build on an efficient ray-tracing engine”
“a platform for a ‘virtual test environment’ that could provide a powerful, cost-effective capability for survivability and lethality evaluation.”
1998 Assessment of the Army Research Laboratory,ARL Technical Assessment Board, National Research Council
CSG BREP Splines BREP Facets
radius(r)
vertex(x,y,z)
4 numbers
20 knot values
45 control pts(x,y,z)
45 weights
200 numbers
287 triangles
~287 vertices (x,y,z)
~861 numbers
CSG is most storage efficient
Data Storage Comparison