Visible Landmarks Research Articles

Topological direction-giving and visual navigation in large environments

In this paper, we propose and investigate a new model for robot navigation in large unstructured environments. Current models, which depend on metric information, have to deal with inherent mechanical and sensory errors. Instead we supply the navigator with qualitative information. Our model consists of two parts, a map-maker and a navigator. Given a source and a goal, the mapmaker derives a navigational path based on the topological relationships between landmarks. A navigational path is generated as a combination of “parkway” and “trajectory” paths, both of which are abstractions of the real world into topological data structures. Traversing within a parkway enables the navigator to follow landmarks that are continuously visible. Traversing on a trajectory enables the navigator to move reliably into featureless space, based on local headings formed by visible landmarks that are robust to positional and orientational errors. Reliability measures of parkway and trajectory traversals are defined by appropriate error models that account for the sensory errors of the navigator, the population of neighboring objects, and the rotational and translational errors of the navigator. The optimal path is further abstracted into a “custom map”, which consists of a list of symbolic directional instructions, the vocabulary of which is defined by our environmental description language. Based on the custom map generated by the map-maker, the navigating robot looks for events that are characterized by spatial properties of the environment. The map-maker and the navigator are implemented using two cameras, an IBM 7575 robot arm, and a PIPE (Pipelined Image Processing Engine.)

VISLAN: computer-aided surgery

Measurement systems using video cameras and image processing have matured to the point where they can guide surgeons. This article is mainly about VISLAN (VISible LANdmarks), a particularly challenging application of computer vision to support neurosurgery-but there are several examples of similar techniques being applied in more routine situations. Some of these examples are discussed. VISLAN involves navigating surgical instruments inside the skull. The potential benefits are substantial in VISLAN's medical application. The risks of surgery will be reduced by enabling plans to be followed more accurately Alternatively, the ability to follow detailed plans can allow the surgeon to undertake more complex procedures than would otherwise be contemplated. There are also benefits in lower costs, because additional preoperative scans for surgical planning may be avoided and the length of operations may be shortened reducing the risk of surgery.

Optimized vertical stereo base radiographic setup for the clinical three-dimensional reconstruction of the human spine

This paper presents a method to determine the stereoradiographic planes and anatomical vertebral landmarks giving the most reliable three-dimensional reconstructions of the thoracic and lumbar spine for clinical studies. The present investigation was limited to stereoradiographic setups with a normal vertical stereo base. Possible X-ray tube positions are thus corresponding to angles ranging from 0 (conventional posteroanterior radiograph) up to 30° (dimension of the X-ray room). An X-ray phantom was used as a specimen from which three-dimensional reconstructions with the direct linear transformation (DLT) algorithm were obtained. Visibility of landmarks located on pedicles, end-plates, transverse and spinous processes was evaluated for the whole thoracic and lumbar spine (T1 to L5). Process landmarks were discarded because their poor visibility on radiographs produced inaccurate three-dimensional reconstructions. Considering the size, shape and orientation of vertebrae, an angle of 20° between the posteroanterior horizontal position and the angled position of the X-ray tube gave optimal results. Landmarks located on pedicles and end-plates produced the most reliable three-dimensional reconstructions of the spine. Pedicles were found to be more reliable landmarks than end-plates. Validation of the technique with reconstructed steel beads reveals three-dimensional errors under 1.0 mm. Since vertebral landmarks were more difficult to identify on radiographs than steel beads, reconstruction results were compared with those obtained with a biplanar orthogonal setup. This shows that three-dimensional errors of 8.0 mm may be expected on actual reconstructions of the spine and errors as large as 15.0 mm may be present on poorly visible landmarks.

Mobile robot visual mapping and localization: A view-based neurocomputational architecture that emulates hippocampal place learning

We propose a real-time, view-based neurocomputational architecture for unsupervised 2-D mapping and localization within a 3-D environment defined by a spatially distributed set of visual landmarks. This architecture emulates place learning by hippocampal place cells in rats, and draws from anatomy of the primate object (“What”) and spatial (“Where”) processing streams. It extends by analogy, principles for learning characteristic views of 3-D objects (i.e., “aspects”), to learning characteristic views of environments (i.e., “places”). Places are defined by the identities and approximate poses (the What) of landmarks, as provided by visible landmark aspects. They are also defined by prototypical locations (the Where) within the landmark constellation, as indicated by the panoramic spatial distribution of landmark gaze directions. Combining these object and spatial definitions results in place nodes whose activity profiles define decision boundaries that parcel a 2-D area of the environment into place regions. These profiles resemble the spatial firing patterns over hippocampal place fields observed in rat experiments. A realtime demonstration of these capabilities on the binocular mobile robot MAVIN (the mobile adaptive visual navigator) illustrates the potential of this approach for qualitative mapping and fine localization.

Topographical variation of the human primary cortices: implications for neuroimaging, brain mapping, and neurobiology.

The relationships of the "primary" cytoarchitectonic neocortical fields, 17, 41, 3b, and 4 (Brodmann areas), to salient topographic landmarks have been reconstructed from serial histological sections in 20 human cerebral hemispheres (10 brains). Each of these architectonic fields is found to bear a characteristic relationship to a set of enframing anatomic landmarks, in particular, gyri, fissures, and sulci, that can be readily defined by MRI. Two classes of variability were found characteristic, at least to some extent, of each of the fields. Class 1 variability--variability that is not predictable from visible landmarks--was typical of the polar and for the cuneal and lingual extracalcarine distributions of field 17 and the distribution of field 4 upon the paracentral lobule. Class 2 variability--variability that is closely predictable from visible landmarks--is seen in the marked interindividual or interhemispheric variation in size or shape of a field and was found to be prominent for all four fields. Because of the prominence of class 2 variability, direct reference to the landmarks that frame these fields may be expected to be a more reliable basis for functional mapping than reference to a template or stereotactic coordinate-based system of reference to a standard or idealized brain.

Cochlear Nucleus Anatomy Related to Central Electroauditory Prosthesis Implantation

The central electroauditory prosthesis is now used to stimulate the cochlear nuclei to obtain auditory perception in patients with bilateral cochlear nerve transection who are undergoing bilateral acoustic tumor removal. In this study, we used fixed cadaver specimens to identify visible landmarks for accurate placement of the central electroauditory prosthesis through a combined suboccipital-translabyrinthine opening. Histologic features of the regions of probable implantation of the central electroauditory prosthesis were also investigated. We found that the following landmarks might have surgical significance: (1) the tenia of the inferior velum of the fourth ventricle, which crosses the surface of the ventral cochlear nucleus and the vestibulocochlear nerve; (2) the angle between the vestibulocochlear and glossopharyngeal nerves; and (3) the foramen of Luschka. It is suggested that an incision be made in the tenia for insertion of the prosthesis into the lateral recess and eventual placement on the ventral cochlear nucleus surface. To study regions of potential stimulation, we injected ink into different sites on the exposed surface of the cochlear nuclei. We then histologically examined neuronal populations adjacent to the sites. We found that a portion of the ventral cochlear nucleus localized within the lateral recess might be the most appropriate location for placement of the central electroauditory prosthesis.

Judgments of eye level in light and in darkness.

Subjects judged eye level in the light and in the dark by raising and lowering themselves in a dental chair until a stationary target appeared to be at the level of their eyes. This method reduced the possibility of subjects' using visible landmarks as reference points for setting eye level during lighted trials, which may have contributed to artificially low estimates of the variability of this judgment in previous studies. Chair settings were 2.5 deg higher in the dark than in the light, and variability was approximately 66 percent greater in the dark than in the light. These results are discussed in terms of possible interactions of two separate systems, one sensitive to the orientations of visible surfaces and the other sensitive to bodily and gravitational information.

Cues for orientation in hummingbird foraging: color and position

In this study we examined the relative influence of the color and position of food sources on the feeding patterns of hummingbirds. We studied ruby-throated hummingbirds (Archilochus colubns) in the field and rufous hummingbirds (Selasphorous rufus) in the laboratory. The field experiments demonstrated that the use of equally profitable feeders in arrays is more strongly influenced by position than by color. This suggests that hummingbirds learn and remember the locations of profitable food sources and return to them preferentially if the reward continues to be adequate. The laboratory experiments demonstrated that although hummingbirds learn quickly to return to a single profitable feeder in a linear array of unprofitable ones if it is marked by a consistent color cue, their learning is strongly influenced by position in the absence of color cues. This suggests that hummingbirds' spatial memory may be limited in resolution and that they may use visible landmarks to improve their performance. These results are consistent with the hypothesis that landmarks facilitate foragers' limited ability to learn and remember profitable locations in their environments.

Nueva estación central de Varsovia, Polonia

The inauguration of this station, one of the three long-distance stations in the city, has provided a series of advantages for the Capital, amongst which is the comfortable and fast access of the passengers to the canter of the city and the decongestion of urban transport systems. Regarding its architectonic dimensions, the building satisfactorily fulfills the two main purposes imposed from the very beginning of the planning stage —its integration in the urban surroundings and the street system— and at the same time it constitutes a visible landmark to guide the public and it has also been adapted to the different train, automobile and passenger routes, without interference and minimum runs. Regarding this second point, and thanks to the proper organization of itineraries, in the future the station will be able to hold a considerably larger number of passengers than foreseen in the project estimates without having to increase the number or size of the installations.

Image Stretching on a Curved Surface to Improve Satellite Gridding

A method for substantially reducing gridding errors due to satellite roll, pitch and yaw is given. A gimbal-mounted curved screen, scaled to 1:7,500,000, is used to stretch the satellite image whereby visible landmarks coincide with a projected map outline. The resulting rms position errors averaged 10.7 km as compared with 25.6 and 34.9 km for two samples of satellite imagery upon which image stretching was not performed.

Biochemical aspects of early differentiation in vertebrates.

Publisher Summary This chapter reviews the information about changes in DNA, RNA, and protein during successive phases of embryonic development in vertebrates. It discusses cleavage and pregastrulation stages. Mammal embryos have been studied in toto until the blastocyst stage when two cell types can begin to be distinguishable based on their grouping and shape. In avian and reptilian embryos, little is known of the stages prior to primitive streak formation because the streak is the first visible landmark of differentiation. In contrast, in amphibians, much more is known of events during cleavage because there are visible differences between the cells such as the size, yolk content, and pigmentation that make them distinguishable for comparative studies. The chapter presents findings on amphibians; these findings have formed the basis of most of the recent thinking about differentiation in vertebrate embryos. Every developing tissue in vertebrate embryos depends to some extent on neighboring tissues for its normal differentiation. The chapter reviews recent work on neural induction and the interactions in the early embryonic axis.

ELECTRICAL EXPLORATION OF THE INTERNAL CAPSULE AND NEIGHBOURING STRUCTURES DURING STEREOTAXIC PROCEDURES.

T He. var iabi l i ty in position, shape and size of deep cerebral s t ructures in relat ion to radiologically visible landmarks hard ly needs to be stressed again and even the mos t careful p lot t ing of a t a rge t point and the mos t precise ins t rumenta t ion leave a margin of error which becomes more impor t an t as the t a rge t is s i tuated fa r the r away f rom the l andmarks used to plot its position. I n an effort to compensate for or minimize this error in localization because of unpredictable ana tomica l variat ions, workers in the field of stereotaxic surgery have used various physiological methods to obta in a more precise identification of the deep structures involved in the projected lesion or of other neighbouring s tructures which it is desirable to avoid. In our modes t series of stereotaxic operations for the t r e a t m e n t of involuntary movements a t the Mont rea l Neurological Inst i tute, we have found such physiological explorat ion of the area in which we planned to make our lesions an ext remely useful if not indispensable tool. In this presentat ion, we shall repor t on the results of this explorat ion in s procedures carried out on ~ pat ients .

Roentgenographic Examination of the Sphenoid Sinuses

THE reasons for writing this paper are: 1. To present in concrete form the result of our experimental and clinical study of the sphenoid sinuses with the roentgen rays during the past three years. 2. To demonstrate the necessity for a rigid adherence to our technic. 3. To answer constructive criticisms. 4. And lastly, to prove the superior diagnostic value of our method. As the logical development of the nasofrontal and naso-mental positions and while attempting to obtain greater uniformity and better duplication when making roentgenographs of the sphenoid, we devised the head rest or sinus mask, without which the alveola-glabella position of the head would be impossible. In a former communication (1) we showed the uniformity obtainable with the use of the alveola-glabella position when making roentgenographs of different heads, and the duplication possible with the same head. We recommended a 107° angle inclination of the head and the use of a vertical ray for the best unobstructed view of the sphenoid sinus, and showed constant and clearly visible landmarks for the upper boundaries of the sphenoid and ethmoids (2). In a later communication (3), we proved what anatomical structures produced these landmarks and emphasized the diagnostic importance of the curved sphenoid line, or Granger line, and of the sphenoid region included between that line and one lower down which forms the upper border of the ethmoids. (See key plate, Fig. 1.) This region represents the upper anterior portion of the sphenoid sinuses projected through the frontal sinuses. This view is best obtained (as shown in Fig. 2) by placing the cassette covered with the sinus board or mask on a 17° angle block arranged so as to give to the sagittal plane of the head a 107° inclination. The nose must be inserted in the aperture in the sinus mask, and the upper jaw (alveola) and a line uniting the eyebrows (glabella) must rest firmly on it. The central ray is directed vertically through the head on a line just below the external auditory meatus. We cannot insist too strongly upon the fact that the head must rest and bear firmly and evenly on the alveola and the glabella, and that the angle block must have an angle of exactly 17°. If this is done, the roentgenographs will resemble the key plate, Figure 1, and B of Figure 3. It will be noted that in both these roentgenographs the shadow of the petrous bone is situated in about the center of the orbit and does not extend beyond the upper or lower borders of the latter.

A Journey on the Rio Zamora, Ecuador

The Andes of Ecuador part into two main parallel ranges, known as the Cordillera Occidental and Cordillera Oriental, united at intervals by transverse ridges of inferior height, designated by the Spanish topographical term of nudos, literally knots.l The southernmost of these is the Nudo de Cajanuma, which forms the divide between Pacific and AmazonAtlantic drainage; some twenty-five miles to the north is the Nudo de Acayana y Guagra-uma; and enclosed between the two and the lateral mountain chains is the Basin of Loja (Hoya de Loja). The opposite inner faces of the two Cordilleras are here physiographically similar, but the outer, or Pacific and Amazon versants, respectively, are in distinct contrast. The former, through the withering action of the hot, dry air currents borne up the Catamayo valley from the desert littoral of Peru, is bare of vegetation, while the latter, under the benign influence of perennial rains, is clothed with dense tropical forest. In the intermontane depression between the two ranges, at an elevation of 2,150 meters (7,053 feet) above sea level,2 stands the town of Loja. Due west of it the isolated and sharply outlined peak of Villonaco (3,220 meters, or 10,560 feet) rises from the relatively low profile of the Cordillera Occidental, forming a dominant feature of the local topography and a widely visible landmark. It is interesting to note that certain neighboring eminences, Fierro-urcu (3,788 meters, or 12,430 feet) and Colambo (3,094 meters, or 10,150 feet), were occupied as trigonometrical stations in the great triangulation carried from Tulcan, on the Colombian frontier, all through Ecuador down to Payta, in Peru, by the French geodetic commission in 1899-1906, in their revision and extension of the work of the academicians Bouguer, La Condamine, and Godin in the eighteenth century for the measurement of an equatorial arc of a meridian.3 The lower slopes of the Cordillera Oriental about the Hoya de Loja are