Rapid Construction Of Three-dimensional Sand Table Model Based On GF-1 Imagery

Sand table is widely used in the education,construction,military and other industries.The traditional method of making sand table is based on contour data,and it is generally made of sand,cement,foam and other materials by people.Because of its low precision and long cycle,the traditional sand table is difficult to adapt to the current requirements of the society.With the development of the remote sensing,three-dimensional printing and computer technology,it could be possible to make a high precision,short cycle,enabling personalized and informative three-dimensional sand table model.Based on GF-1 image,shadow detection,shadow enhancement,and based on digital elevation model,modeling,texture mapping and gypsum-based three-dimensional printing were made in this thesis to explore the three-dimensional printing technology of making sand table model.Firstly,the classifications of three-dimensional printing rapid prototyping were introduced in this paper,including stereo lithography apparatus,selective laser sintering,fused deposition modeling,laminated object manufacturing and 3D printing’s principle,advantages and characteristics were summarized.Using gypsum-based three-dimensional printing technology for its color high precision and saving material to make the color three-dimensional sand table model.At the same time,digital elevation model could convey exactly three-dimensional information to people,and finally used digital elevation model to make three-dimensional sand table model.Because of the high resolution,multispectral,short cycle and so on,the texture data of sand table could be comprehensively expressed by using GF-1 satellite image data,and the ground surface information could be comp rehensively expressed.Secondly,image shadow is not only has advantages in the shadows,but also disadvantages.For this reason,aiming at the GF-1 image commonly used in geographical condition monitoring,this paper presented a shadow detection method based on feature of city of tall objects in the GF-1 imagery.A new Shadow Index on shadow detection was proposed based on characteristics of shadow,HSV color space and principal component transformation.Then this method and principal component transformat ion detection method were compared.The results showed that the proposed shadow detection model could effectively distinguish shadow region with water,dark vegetation and partial blue objects and the model could distinguish between dark objects and shadow areas.In the case of artificial turf,this method could effectively distinguish artificial turf and shadow region.After shadow detection,this article was based on the basic principle of Homomorphic filtering and characteristics of the shadow,in frequency range,the Homomorphic filtering was employed to process the image.The shadow was enhanced by the Homomorphic filtering which the high frequency component was increased while the low frequency component was reduced.A new model on shadow enhancement was proposed based on Homomorphic filtering and Mask.Then this method and traditional Homomorphic filtering were compared in a test area.Experiment showed that the proposed shadow enhancement model had a good shadow removal and did not change the non-shaded area.Then,the pretreatment of using image to make sand table model was completed by the shadow detection and shadow enhancement.The image dodging was realized through Photoshop software,and the texture data was finished finally.Thirdly,this paper detailed the process of rapid prototyping and summarized,such as the making of digital three-dimensional model,the layering of digital three-dimensional model and the setting of gypsum-based three-dimensional printer.According to the present software platforms are imperfect and incompatible,and other issues exist in as well.The paper summarized on the advantages and disadvantages about data processing,including Global Mapper,Geomagic,Magics,Zbrush,and Maya.In addition,the paper gave some ideas between all kinds of software platforms by making sand table model.The process of making sand table model could make full use of advantages of every software platform and could make the sand table more quickly and accurately.Finally,the color three-dimensional sand table model was output by the gypsum-based three-dimensional printing technology.The solutions of printing quality problems(such as terrace phenomenon is serious,height error,and so on)were studied.