Application Development Research On Oblique Conical Projection Module Based On Module Technology

The geography is a kind of space science, geography information science is also a science using space information as backbone. The significant mark between GIS and other kind information is that geography information belongs to space information and others are not. Geography datum framework plays a key role in expressing geography information scientifically, whose location-recognition keeps close touch with data. Among so many geography datum frameworks, map projection is the only one which can directly incarnate in visualization. It is not only the important constituent of map mathematics foundation, but also the control skeleton and the basis of localization which accurately draws the scenery from the surface of Earth ellipsoid to the planar drawing.The type of map projection has diverse. From a global point of view, the projection of large and medium scale topographic map in every country has not been unified now. According to incomplete statistics, there are more than ten kinds of map projections. And the Most commonly used is Gauss-Kruger projection and so on. As we all known, normal conical projection is used to make medium -latitude maps which spread out on either side of east and west. However, the shape of study area is irregular, which can not extend in the special latitude or longitude, such as the coastal zone in our country and Inner Mongolia Autonomous Region whose shapes are similar to arc-shaped, so they can not be fitted perfectly to make the deformation least either adopted normal projection or inverse projection. In this case, oblique projection, which can fit the region line or region surface shape better, plays its unique advantage. The oblique conical projection may make the spatial expression continuously and distortion lowest in special study area, then realizes the integrated expression of region.The software we often used in GIS has not defined oblique projection, which brings a big inconvenient to the application of oblique projection. Combine with specific research in this paper, we make full use of ArcObjects in the ARCGIS environment to develop a transformation module which can transform map projection we used to oblique conical projection. With a practical example, the paper makes a study from the following aspects: 1) The design of oblique projection, 2) The transformation between common projection and oblique projection, 3) The realization of transformation module based on ArcGIS. Among all the problems, the derivation of projection formula and establishment of the Pseudo-pole is most important. In this paper, we achieved a transformation from several common projections to oblique conical projection, at the same time, we can also transform the longitude - latitude coordinate to oblique conical projection directly. The key point of this transformation is the establishment of Pseudo-pole. In the process of transformation we can take the mean value of zenith angle that the Pseudo-pole makes with the arc which is constitute with points we get, and then establish the geography space datum for oblique conical projection used the parameter we gained. According to the transformation relationship between the geographic coordinate system and oblique conical projection, then realize the transformation between the two.The oblique conical projection keeps our coastal zone integrity in most degree and makes the distortion to be lowest, which application role is extremely obvious in China's coastal zone, All of those are conducive to the seamless roaming under the GIS environment, and they can also meet the need of scale non-rank change to a great extent in the coastal zone information visualization, which put a solid mathematics foundation for China's coastal zone research. In addition, the oblique conical projection can also be applied in these study area where the extending is not in special latitude or longitude direction.