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# SELECTED TOPICS IN COMPUTER SCIENCE CS 419

OSU

GPA 3.95

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This 13 page Class Notes was uploaded by Mrs. Maximo Lueilwitz on Monday October 19, 2015. The Class Notes belongs to CS 419 at Oregon State University taught by Staff in Fall. Since its upload, it has received 40 views. For similar materials see /class/224505/cs-419-oregon-state-university in ComputerScienence at Oregon State University.

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## Reviews for SELECTED TOPICS IN COMPUTER SCIENCE

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Date Created: 10/19/15

Software Review Peter Sandin Policy Kit March 9 2008 What is Policy Kit Policy kit is an extension to the hardware abstraction layer mount helpers and other DBUS aware applications that need elevated privileges on Linux systems The goal ofpolicy kit is to provide finer grained control over administrative functions in modem desktop environment Currently the levelso quot quot mu Ilmntacce amiuiu 39 l quot quot 39 39 access to administrative functions for users While sudo can be con gured to provide tight control based on groups and complex set of sudoers rules it is anontrivial dare I say daunting to setup and must be done by hand editing the sudoers le Policy kit aims to refine this by providing authentication for specific actions as identi ed by their DBUS interface based on where the user is logged in from 39 in L 39 39 roup Policy Kit I 39 rom anyone console local and the active console For each action a level of access is defined for each scope levels ofaccess range from at 39 39 with 39 39 user and an administrative user in between Policy Kit started in the Fedoraproject to try and fix the short comings ofthe existing HAL mounting helpers Policy Kit was rst implanted in Fedora Core 8 to manage mounting of USB disks Since then Policy Kit has been expanded to include handling privileges for more DBUS aware app ications The next version ofpolicy kit is set to be rolled out in FC9 and Ubuntu 804 The next generation of policy kit will support Power Management control over bluetoothwifi radios HAL configuring Policy Kit itself Wake on LAN settings and clock and timezone settings The clock settings are the first elements ofPolicy kit to extend beyond hardware management With the support of Fedora and Ubuntu Policy Kit39s use and integration within the Gnome desktop is likely to expand over the next couple of releases Installation NA Policy Kit is tightly bound in to the Gnome desktop and really isn39t designed to be installed independently RPM and Deb packages are available for Fedora and Ubuntu but Policy Kit comes preinstalled Lucatum V Easeostegt r Policy Kit is anewtechnology and it shows The interface and often lack there of exposedto the end user is an elegant and unobtrusive way to allow them elevated privileges when needed The default settings that ship with Ubuntu 804 Alpha6 are good they allow the user access to media and other settings they did not have non administrative access to previously The problem with policy kit is that it39s configuration interface is an ambitious mess There39s a lot in the way of documentation and obvious visual cues missing as to what the authentication scopes are The names of the levels of access are pretty clear No Administrative Authentication Time Authentication Time Yes The yes and no options are just that The time options are one shot none speci ed not sure how this is different than session keep for the session keep inde nitely The biggest problem with setting up the con guration is that it39s not very clear exactly what each key does The only information that you get on them is name of the DBUS entity the policy applies to a v a mg 7 Action V 3 9mm Identi er urg freedesktup pulitykit modifydefaults Desclipnan39 Modify defaults furlmplmt authorizations one line description of the key and v g cluzkapplet The W m m m the name of the vendor respons1ble V B Wm y t t r mplicit Autharizations for that policy The problem is that the 9 we 5 539quot WE 1 i mpliEit authorizations are authorizations key names are down right cryptic and titans um H i Anyone Nu don t really tell you what they are v g freedesktup Console Nu unless you already know what they v 3 systemtumsbackends 7 AcnveConsnle AdminAuthentizatiun one shut do The descriptions aren39t much Q Mmgesymmmmm 7 quotEdi 7777777 will Reve wem l 39 V g self i better they re usually a Slngle Q creme usercun gurat Explicit Authorizations 39 39i quot Th39itdi th t tht sentence Wthh 1511 t Very descrlPthe V 3 WW eit ie cha ng ruuzrhzgufhnsmi tfdur and just by size constraints alone can39t even begin to describe what the key Blocked authorizations are marked with a Q Read authorizations ur utr 570 Sign lt3 Muddy defaults furimphci Emmy 5mg 93 actually COHtTOIS Alld the Vendor lt7 Grantauthurilatmnstuut Peterrleter pid1935Busrbinpulkitrgnnni 7 name is the least useful of all the v a hal mil elements because the vast majority of V 1 quot quot i l m them are blank Features Once again Policy Kit is new once it39s been around longer it will be better integrated and will support a wider range of applications and functions Right now the number of application and functions that policy kit supports is pretty much a joke it39s only practical application in it39s current state is configuring the clock and timezone HAL has been ported to use Policy Kit to determine its access rights but the defaults that it ships with are functionally equivalent to the the existing HAL helpers As more application gets ported to Policy Kit it has the potential to change they way permissions and privilege escalation are handled It s not going to change the world from the end user39s perspective but the fine control it will give system administrators will be a big boon once it39s in place Also once it39s universal it will allow better defaults control schemes to be shipped allowing tighter one shot authentication for things that needed it laxer authentication session inde nite for areas where it39s not needed and background approval Yes for things that are technically administrative functions but really should be available to regular users Overall It s open source software Policy Kit adheres to the mantra release early release often In it39s current state its pretty much a novelty but by getting they39re going to get lots of requests suggestions and bug xes It has lots of potential but right now Policy Kit just isn39t ready for prime time Hopefully they can come up with a better less ambiguous con guration interface The good news for end users is that even if the con guration isn39t friendly the default settings are at least sane and usable If we39re lucky Policy Kit will be ready for prime time in time for quotThe year of the Linux desktopquot Rotations and Interpolation Ron Metoyer CS419519 Computer Animation r 39T Moving Objects ltransformations review Can move objects 3D using translation keyframing allows us to guide that movement lt gtWe can also orient objects in 3D keyframing also applies to orientationor rotations moving things in computer graphics is accomplished through transformations lt gttransformations are matrices that can be multiplied by a point a vector to produce a new point a new vec or Transformations lt gtTranslation Scaling and rotation work as f ollows Translation Scaling add Rotation multiply Homogenous Coordinates In graphics we use homogenous coordinates for all transformations 4x4 matrix can be used to represent translation rotation scaling and other transformations Since we re dealing with 3space the 4 11 coordinate is typically 1 15 WWW1 mm 1211qu Translation Hrx 1 0 0 rx 6 yty 7 0 1 0 y y 2H 7 0 0 1 t z 1 0 0 0 1 1 wheredolhe points come from new point in transformation pomt In space matrix Scaling 62 xSX SX 0 0 0 x ySy 0 Sy 0 0 y zSz 7 0 0 s 0 z 1 0 0 0 1 1 Rotation 2D x rcosg y rsinq x rcosi9 x rcosBcos 7sin sini9 y rsini9 y rcos sini9sin cos l9 x39rcos cos irsin sini9 Hxcosi97ysiru9 y39rcos sini9rsin cosi9 y39xsiru9ycosi9 J Rotation 0 0 x rsm o y Xaxis c053 0 z 0 1 1 sine 0 x 0 0 y Yaxis c053 0 z 0 1 1 x39 cos rsm 0 0 x y39 sine cose o o y Zaxis z 7 o 1 o z 1 0 0 0 1 1 Transformations We can now treat all transformations the same as a series of matrix multiplications PEMMMMAMSMP MMiM2MzM4MsM6 pew InBetween Transformations In order to move objects we need translations and rotations lt gtWe ve seen that keyframing allows us to specify startend positions keys interpolation type and speed in order to get new positions the inbetweens GWWe can do the same with the orientation of the objectbut rotations are slightly different lOrientation Representations How best do we represent orientations of an object and interpolate orientation to produce motion over time Rotation Matrices Figtlted Angle Euler Angle Agtltis Angle Quaternions Rotation Matrices QOrientation of an object can be viewed as a composite series of 3 rotations about gtltyz agtltes resulting in a single 3gtlt3 matrigtlt QRotation matrices have two VERY important properties UNIT ORTHOGONAL Property rows and columns are unit length Property rows and columns are orthogonal Ifthese properties do not hold the matrix is not a proper rotation matrix Rotation Matrices anterpolating the matrix components does not guarantee that these properties hold linearly interpolate from a 90 degree rotation about y in a 90 degree rotation about y 0 0 1 0 0 71 0 1 0 p 0 1 0 71 0 0 1 0 0 Linearly interpolate each component and halfway between you get this 0 o o No longer arotation 0 1 0 matrix since not 0 0 0 onhononnal lEuIer Angles and Fixed Angles We could represent rotations as the angles rotated about each principal axis Two ways to view independent axis angles 2 ways to think about them Moving coordinate system Euler Angles Figtlted Coordinate system Figtlted Angles Fixed vs MovingEuer Fixed rotatel R translateT 1 X X 1 P39 TRP Moving Euler J Y translate T rotatelR vl X Euler vs Fixed V Euler Angles Write matrix multiplication left in right with respect in the Q Fixed Angles new coordinate system Write the matrix multiplications right to left with respect in the xed coordinate system These are just two ways to THINK about tations you get the same answer either way Fixed Angle and Euler Angles 7 Quientations are speci ed by a set of 3 ordered parameters that represent 3 ordered rotations Treat each axis independently and interpolate I Y Z H oblems Noturllque e glvel l two orlel ltanol39lsofal39l object there are several Euler angle combll lauol39ls that take you from A to B Glmbal Lock Not Unique J Gimbal Lock A 90 degree rotation about the y axis essentially makes the first axis of rotation d align With the thlr Y lb lg x Z z Rutxl RUMBU mm Olncremental changes in xz produce the same results you39ve lost a degree of freedom Gimbal Lock I Espeeiany aproblem ifinterpolating say 0900 gt 904590 Halfway you d expect 90 22 5 90 but get 45 e7 5 45 y y y Z Z Initial Orientation 2 object Space 0900 90 45 90 Angle and Axis Any orientation can be represented by a 4 angle vectorxyz where the angle is the amount rotate by and the vector is the axis 0 rotate Can interpolate the angle and agtltis separately No gimbal lock problems QBut can t ef ciently compose rotationsmust convert to matrices first We can easily convert between matrix and axisangle so it s a good option Quaternions The best of both worlds Axisangle type representation with good interpolation unique interpolations and no gimbal lock Can be multipliedcomposed Quaternions 4tuple of real numbers sgtltyz or sv s is a scalar v is a vector lt0gtSame information as axisangle but in a different form lQuaternion Math dotpmduct xisvi152Vzii3952V VzFi39Vsz39ViXVU A point in space is represented as 0v scalar mult 1000 multiplicative identity 4quot lIIIIII2 er where lsz x2 y2 22 qqquot 1000 the unit length quaternion Conjugate of a quaternion q is a Liv Quaternion Rotation To rotate a vector v using quaternion math represent the vector as 0v represent the rotation as a quaternion q which must be a unit quaternion q Botany cos62sin 92 x y 2 VI Rmv qvq inv conj for unitquat Looks good so farwe can easily specify and compose rotations Quaternion Interpolation Quaternions represent points on a hypersphere Direct linear interpolation does not suffice lQuaternion Interpolation QUse a special interpolation technique Spherical linear interpolation viewed as interpolating over the surface ofa hypersphere sin17ul9 sin u 512qu q2 u q 7 qz sm 9 sm 9 QAS in linear interpolation in Euclidean space we can have first order discontinuity Solution is to formulate a cubic curve interpolation Rotations in Reality lt gtIt s easiest to express rotations in Euler angles or Axisangle that s how most UI s wor lt63gtWe can convert tofrom any of these representations Choose the best representation for the task input Euler angles Fixed Angles interpolation quaternions axisangle composing rotations quaternions orientation Summary of Keyframing We know how to move points in 3D translation and rotat39on lt gtSo we can set keyframes pos orientation lt We can describe interpolation methods linear cubic polynomia QWe can control interpolation speed with speed curves and arc g h reparameterization

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