<p>As the volumes are entering the world of computer graphics the pure volume visualisation becomes a more important tool in for example research and medical applications. But the advance in haptics --- force feedback from the computer --- is behind. In volume haptics no equal to the proxy method so popular in surface haptics has yet emerged. Some implementations of volume haptics even use surfaces as intermediate representations so that surface haptics can be used.</p><p>The intention of this work was to create natural feeling haptic feedback from volumetric density data using pure volume haptics. The haptic algorithm would be implemented in Reachin API for the Reachin Desktop Display, together with other parts to build up a usable volume visualisation environment.</p><p>To achieve the feeling of stiffness and friction dependent on tissue type, a proxy based method was developed. In the volume the proxy is constrained by virtual surfaces defined by the local gradient. This algorithm was implemented in a volume haptics node and for visualisation a volume renderer node was implemented. These nodes can be used to setup different volume visualisation environments using VRML.</p>

Stroke is the third largest cause of death in Sweden. In 2005, 30.000 people in Sweden suffered from a stroke. The consequences of a stroke varies, but the most common disability among stroke survivors is abnormal reaching movements, which is the primer reason for limitations in activities of everyday living. Rehabilitation is essential in order to get back to everyday life. Physical assistance (or guidance) is used in rehabilitation by physiotherapists and occupational therapists to help a patient through a dicult movement for example. Today, this guidance is limited to be performed by medical personnel. With the technology of virtual environments (VE) and haptics – force feedback from a computer – there is a possibility to create guidance which does not need medical personnel. This should be used as a complement to the traditional therapy. The intention of this work is to create an invisible guidance eld, which should guide a patient's hand to a desired movement pattern, i.e. aid the patient to perform a task in a virtual environment with haptics. This guidance is added to an already existing assessment tool, which is a part of the Curictus AB rehabilitation system. The guiding system is implemented using SenseGraphics AB's H3D API. To create the feeling of guidance and a guidance eld, the Volume Haptics Toolkit, developed by Dr. Karljohan Lundin Palmerius at Linköping University, was used. The basic idea of the algorithm is to calculate an orientation vector, for every position, in which direction the guidance should guide the patient. The guidance, which is generated via a haptic device, is adaptive to the patient's movements and always guides the patient towards the target in a smooth trajectory. / Stroke är den tredje största dödsorsaken i Sverige. Under år 2005 ck 30.000 svenskar en stroke. Följderna av en stroke kan variera, men vanligast är försämrad rörlighet i en sida av kroppen, vilket också är den främsta orsaken till begränsningar i dagliga aktiviteter för  strokepatienter. Rehabilitering är nödvändig för att kunna återkomma till sitt vanliga liv. Fysisk guidning är något som sjukgymnaster och arbetsterapeuter använder sig av i rehabiliteringen för att hjälpa en patient t.ex. genom en svår rörelse. Denna hjälp är något som idag är begränsad till medicinsk personal. Med teknologi som virtuella miljöer och haptik – kraftåterkoppling från en dator – finns det möjligheter att skapa guidning som inte kräver medicinsk personal. Detta ska fungera som ett komplement till den traditionella rehabiliteringen. Avsikten med det här arbetet är att skapa ett osynligt guidningsfält som ska guida en patients hand till ett önskat rörelsemönster, d.v.s. hjälpa patienten att utföra en övning i en virtuell miljö med haptik. Denna guidning ska läggas in i ett redan existerande utvärderingsverktyg, som nns i Curictus ABs rehabiliteringssystem. Guidningssystemet är implementerat i SenseGraphics ABs H3D API. För att skapa känslan av guidning och guidningsfältet användes the Volume Haptics Toolkit, utvecklat av dr. Karljohan Lundin Palmerius vid Linköpings Universitet. Algoritmen är byggd på att för varje position, beräkna en riktningsvektor dit guidningen ska guida patienten via en haptikenhet. Guidningen, som anpassas efter patientens rörelser, guidar hela tiden mot målet i en mjuk rörelsebana.

As the volumes are entering the world of computer graphics the pure volume visualisation becomes a more important tool in for example research and medical applications. But the advance in haptics --- force feedback from the computer --- is behind. In volume haptics no equal to the proxy method so popular in surface haptics has yet emerged. Some implementations of volume haptics even use surfaces as intermediate representations so that surface haptics can be used. The intention of this work was to create natural feeling haptic feedback from volumetric density data using pure volume haptics. The haptic algorithm would be implemented in Reachin API for the Reachin Desktop Display, together with other parts to build up a usable volume visualisation environment. To achieve the feeling of stiffness and friction dependent on tissue type, a proxy based method was developed. In the volume the proxy is constrained by virtual surfaces defined by the local gradient. This algorithm was implemented in a volume haptics node and for visualisation a volume renderer node was implemented. These nodes can be used to setup different volume visualisation environments using VRML.