Abstract: Various aspects of the present invention are shown and described, each of which has stand alone utility in a navigated medical environment. A receiver position calibration system and method facilitates calibration of a reference frame prior to each navigated procedure. A concept and application of confidence weights is introduced. Confidence weights can be applied to distance calculations to mitigate the effects of interference and increase the tolerance of the navigated medical system. Multi-path interference is minimized through the transmission of a signal having a pattern of unique frequencies and filtering of the distance calculations for each frequency to identify the ‘best’ distance in the presence of multi-path interference. A position determination method and system that transmits a signal having multiple frequency components permits positions to be identified with high resolution over a large area.

Abstract: A volume data set composed of voxels is rendered onto an image plane composed of pixels by casting a ray through each pixel of the image plane. A surface of the volume data set is selected as a base plane. Sample points are defined along each ray so that the sample points lie in planes parallel to the base plane. Voxels adjacent to each sample point are sampled to determine a sample value for each sample point, and the sample values of each ray are combined to determine a pixel value for each pixel.

Abstract: A method renders a volume data set as an image in a volume rendering system. The volume data set includes a plurality of voxels stored in a memory. The volume rendering system includes a plurality of parallel processing pipelines. The image includes a plurality of pixels stored in the memory. A set of rays are cast through the volume data set. The volume data set is partitioned into a plurality of sections aligned with the sets of rays. Voxels along each ray of each set are sequentially interpolated voxels in only one of the plurality of pipelines to generate samples only as long as the samples contribute to the image.

Abstract: A plurality of identical rendering pipelines are connected in parallel to read an array of voxels and to write an array of pixels. Each pipeline processes one voxel in one processing cycle of the pipelines. Each pipeline includes a plurality of serially connected different stages. The stages can include interpolation, classification, gradient estimation, illumination, and compositing stages. Interfaces connect identical stages in adjacent pipelines as one-way rings to communicate information associated with spatially adjacent voxels, and delay buffers connected parallel to particular stages communicate information associated with temporally adjacent voxels.

Abstract: A volume rendering integrated circuit includes a plurality of interconnected pipelines having stages operating in parallel. The stages of the pipelines are interconnected in a ring, with data being passed in only one direction around the ring. The volume integrated circuit also includes a render controller for controlling the flow of volume data to and from the pipelines and for controlling rendering operations of the pipelines. The integrated circuit may further include interfaces for coupling the integrated circuit to various storage devices and to a host computer.

Abstract: A method renders a volume data set as an image in a volume rendering system. The volume data set includes a plurality of voxels stored in a memory. The volume rendering system includes a plurality of parallel processing pipelines. The image includes a plurality of pixels stored in an image buffer. A determination is made whether a particular voxel of the volume data set will contribute to the image. The voxel is read into one of the plurality of pipelines only if the particular voxel contributes to a particular pixel of the image.

Abstract: A volume rendering processor renders a two-dimensional image from a volume data set of voxels constituting a three-dimensional representation of an object. Voxel memory interface logic retrieves the voxels from a voxel memory in a scanned order with respect to X, Y and Z coordinate axes, the Z axis being the axis most nearly parallel to a predefined viewing direction. The set of voxels having equal Z coordinate values are referred to as a “slice” of voxels. Interpolation logic calculates a sequence of samples from the retrieved voxels such that (i) each sample lies along a corresponding imaginary ray extending through the object parallel to the viewing direction, (ii) each sample results from interpolating the eight voxels surrounding the sample in the XYZ coordinate system. “Supersampling” in the Z dimension is performed such that the number of samples calculated for each ray is greater than the number of slices of voxels in the volume data set.

Abstract: A method maps samples in a rendering pipelines. The samples are stored in a sample memory. Each sample has a plurality of fields. A descriptor is stored for each field in a field format register. Each sample is read from the memory into a mapping unit. The fields are extracted from each sample according to the corresponding descriptor, and forwarded in parallel to the rendering pipeline.

Abstract: A volume rendering pipeline includes a plurality of processing stages such as a gradient estimation stage, an interpolation stage, a classification stage, an illumination stage, and a compositing stage. The stages are connected to each other by multiplexers. A first multiplexer connects an output of a first stage to an input of a second stage. A second multiplexer connects an output of the second stage to an input of the first stage. A third multiplexer has inputs connected to the output of the first stage and the output of the second stage, the first, second, and third multiplexers are responsive to a select signal to configure the stages of the rendering pipeline for processing the volume data set.

Abstract: A volume data set having voxels arranged according to an object coordinate system is shear-warp rendered by partitioning, relative to the object coordinate system, the volume data set into a plurality of axis aligned sets of voxels. The selected axis aligned sets of voxels are rendered as pixels in intermediate baseplanes. There is one intermediate baseplane for each selected set of axis aligned voxels. The intermediate baseplanes are combined and warped to an image.

Abstract: A volume rendering processor renders a two-dimensional image from a volume data set of voxels constituting a three-dimensional representation of an object. Voxel memory interface logic retrieves the voxels from a voxel memory in a scanned order with respect to X, Y and Z coordinate axes, the Z axis being the axis most nearly parallel to a predefined viewing direction. The set of voxels having equal Z coordinate values are referred to as a “slice” of voxels. Interpolation logic calculates a sequence of samples from the retrieved voxels such that (i) each sample lies along a corresponding imaginary ray extending through the object parallel to the viewing direction, (ii) each sample results from interpolating the eight voxels surrounding the sample in the XYZ coordinate system. “Supersampling” in the Z dimension is performed such that the number of samples calculated for each ray is greater than the number of slices of voxels in the volume data set.

Abstract: A volume rendering system re-samples voxels read from a voxel memory to generate samples along perspective rays cast from a center of projection using a level of detail value. Color computations are performed with the samples to produce pixels for a baseplane image. The level of detail is computed, at each plane of samples perpendicular to a principal viewing axis, from the current sample position and the distance between the center of projection and the baseplane; the principal viewing axis is the coordinate axis in a rendered volume most parallel with a viewing vector. The level of detail provides a measure of the distance between two neighboring perspective rays at each plane and is used to determine the number of voxels and weights for these voxels required to compute a single sample at each plane. Multi-resolution datasets prepared for different levels of details are used to simplify the resampling operation by limiting the number of voxels required to compute a single sample.

Abstract: A method for rendering a three-dimensional volume onto a two-dimensional image plane partitions translucent portions of the volume as defined by polygons into layers. The layers are sorted in a front-to-back order. A near color buffer is set to a transparent color, and a near depth buffer is set to a near clip surface. Then, the layers are processed in the sorted order by initializing a far color buffer to a background color, initializing a far depth buffer to a far clip surface, drawing a current layer into the far color and depth buffers, and rendering the volume, from the near clip surface to the far clip surface, into the near color and depth buffers. After all of the layers have been processed the far color buffer is reinitialized to the background color, the far depth buffer is reinitialized to the far clip surface, and the volume, from the near clip surface to the far clip surface, is rendered into the near color and depth buffers.

Abstract: A method renders a volume data set including a plurality of voxels. In the method, a). the volume data set is apportioned into a plurality of sections. Then, b). a first one of the plurality of sections is rendered by sequentially reading groups of voxels from an external memory and rendering the groups of voxels in the section. Then, c). any accumulated data from the rendering of the first one of the plurality of sections is stored in a temporary storage device. Then, a next one of the plurality of sections is rendered by sequentially reading groups of voxels of the next one of the plurality of sections from an external memory and rendering the groups of voxels, the rendering incorporating accumulated data from the temporary storage device, and then any accumulated data from the rendering of the next one of the plurality of sections is stored in the temporary storage device. Steps d and e are repeated until each of the plurality of sections of the volume data set have been rendered.

Abstract: An apparatus renders a volume data set including a plurality of voxels stored in a voxel memory. The apparatus includes a plurality of pipelines operating in parallel. Each pipeline includes a buffer storing at least one block of at least two voxels of the volume data set. An interpolation stage reads the at least one block of at least two voxels from the buffer. A gradient estimation stage receives an output from the interpolation stage. A compositing stage receives an output from the gradient estimation stage. The apparatus also includes a plurality of interface devices, wherein each interface device couples a particular stage only to an adjacent identical stage in a neighboring pipeline so that identical stages of the pipelines are connected in a ring.

Abstract: A volume graphics device renders a volume data set. The volume data set is apportioned into blocks of volume data, and each of the blocks are apportioned into a plurality of mini-blocks, each mini-block includes at least two voxels of volume data. The volume graphics device includes memory apportioned into a plurality of portions, wherein neighboring blocks of the volume data set are each stored in different ones of the plurality of portions of the memory, and wherein the mini-blocks of each block are stored in consecutive locations in the portion of memory associated with the associated block.

Abstract: Apparatus is provided to enable real-time volume rendering on a personal computer or a desktop computer in which a technique involving blocking of voxel data organizes the data so that all voxels within a block are stored at consecutive memory addresses within a single memory model, making possible fetching an entire block of data in a burst rather than one voxel at a time. This permits utilization of DRAM memory modules which provide high capacity and low cost with substantial space savings. Additional techniques including sectioning reduces the amount of intermediate storage in a processing pipeline to an acceptable level for semiconductor implementation. A multiplexing technique takes advantage of blocking to reduce the amount of data needed to be transmitted per block, thus reducing the number of pins and the rates at which data must be transmitted across the pins connecting adjacent processing modules with each other.

Abstract: A switch for digital communication networks includes a queuing system cape of implementing a broad class of scheduling algorithms for many different applications and purposes, with the queuing system including both a tag-based primary queue which contain ATM cells organized by priority and a secondary queue which contains ATM cells which are not yet scheduled for transmission and which are organized by virtual channel. A queuing decision module is provided to determine in which queue an incoming ATM cell should be deposited. A requeuing module operates when an event occurs that unblocks a particular virtual channel. The requeuing module, on occurrence of such an event, accesses the secondary queue to obtain another cell, to assign it priority and to move it to the primary queue. The queuing decision module, along with a virtual channel table, can be used easily to block virtual channels when necessary. The combination of queues also allows for round robin scheduling.

Abstract: An improvement to a system for controlling traffic in a digital communication network eliminates the necessity for separate buffer queues in a credit-based traffic control system by providing switches at intermediate nodes that provide credit numbers back to the source reflecting either credit numbers from downstream nodes or the numbers of buffers allocated to virtual connections at the node, whichever is the smaller. In one embodiment, this is accomplished by dividing the buffers at a node among the number of virtual connections at that node to establish a number of buffers, each allocated to a different virtual connection, and comparing the numbers of credits received at that node with the number of buffers.

Abstract: High resolution modular large screen displays which can require tens of minutes to display or "paint" an image are updated in real time through the use of active modules, each having its own display device, display driver, processor, memory and interfacing. Communication channels are provided between modules themselves as well as between the modules and a network interface that distributes the video source material in parallel to the modules. The modular approach coupled with the use of active modules permits significant communication reduction that in turn permits real time image production across large areas due to the use of parallel data paths to the display memory distributed across the modules, and through the transmission of structured data, including compressed images, compressed video, sampled data and graphics primitives, permitted by the provision in each module of a processor which converts structured data to images.