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Xianghua Ying

Publications and source records attributed to Xianghua Ying.

3 recordsLinked to original sources

Geometric interpretations of the relation between the image of the absolute conic and sphere images.

A spherical object has been introduced into camera calibration for several years through utilizing the properties of an image conic, which is the projection of the occluding contour of a sphere in the perspective image. However, in literature, only an algebraic interpretation was presented for the relation between the image of the absolute conic and sphere images. In this paper, we propose two geometric interpretations of this relation and two novel camera calibration methods using sphere images are derived from these geometric interpretations.

Algorithms↗

Situation analysis of prenatal diagnosis technology utilization in China: current situation, main issues, and policy implications.

OBJECTIVES: The purpose of this study is to describe the situation with the distribution and utilization of prenatal diagnosis technology in China, to identify some important barriers to prenatal diagnosis use, and to suggest changes to improve the present situation. METHODS: The study uses cross-sectional surveys to capture quantitative data from both providers and consumers. Qualitative information based on focus group discussions is also presented. RESULTS: A mail survey of the provincial Bureaus of Health (BOHs) reveals that sixteen provincial prenatal diagnosis centers and twelve city level centers were accredited by the BOHs by July of 2001. These centers were located in thirteen provinces, of thirty in all of China. Of 147 selected institutions surveyed separately, 90.5 percent offer ultrasound examination, 72.1 percent provide pathogen tests (mainly Toxoplasma, rubella virus, cytomegalovirus, and herpes simplex or TORCH), 57.1 percent do biochemical tests, 21.8 percent have genetic counseling, 13.6 percent do karyotype testing, 7.5 percent do enzymology testing, and 5.4 percent carry out molecular genetic testing. Chromosome diseases, congenital diseases, and several gene diseases are the target diseases. According to qualitative data, macromanagement for prenatal diagnosis, supplier provision of tests, and population demand are the main influences on prenatal diagnosis use. CONCLUSIONS: From the quantitative and qualitative analysis, it is clear that the technology of prenatal diagnosis is not diffusing well throughout China and is apparently not appropriately used. The situation of prenatal diagnosis has implications for policy-makers, including identification of priorities, regulation of prenatal diagnosis, strategic planning, development of guidelines based on health technology assessment, and consumer orientation.

China↗

Catadioptric camera calibration using geometric invariants.

Central catadioptric cameras are imaging devices that use mirrors to enhance the field of view while preserving a single effective viewpoint. In this paper, we propose a novel method for the calibration of central catadioptric cameras using geometric invariants. Lines and spheres in space are all projected into conics in the catadioptric image plane. We prove that the projection of a line can provide three invariants whereas the projection of a sphere can only provide two. From these invariants, constraint equations for the intrinsic parameters of catadioptric camera are derived. Therefore, there are two kinds of variants of this novel method. The first one uses projections of lines and the second one uses projections of spheres. In general, the projections of two lines or three spheres are sufficient to achieve catadioptric camera calibration. One important conclusion in this paper is that the method based on projections of spheres is more robust and has higher accuracy than that based on projections of lines. The performances of our method are demonstrated by both the results of simulations and experiments with real images.

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