Realistic Texture Mapping on 3D Building Models
Fuan Tsai, Hou-Chin Lin
Center for Space and Remote Sensing Research, Dept. Civil Engineering
National Central University, Zhong-Li, Taiwan
Tel: +886-3-4227151 ext. 57619 Fax: +886-3-4364908
E-mail: ftsai@csrsr.ncu.edu.tw,
92322088@cc.ncu.edu.tw
ABSTRACT Three dimensional geo-information is a fast developing topic in remote sensing
and Geographic Information System. Using the technology of remote sensing, 3D building
models can be constructed to resemble real-world building layouts, appearances and other
characteristics. Currently, however, most building models do not have sufficient and accurate
texture information. The lack of texture not only makes 3D building models less realistic, it may
also fail to provide needed information, especially for complex applications such as cyber city
implementation. The purpose of this study is to produce accurate texture mappings on building
models. The textures are generated from mosaic of digital pictures taken from different angles
and distances by free hands. Because of different picture-taking conditions, individual pictures
may have different brightness, shadings, and other properties. All of them need to be addressed
before the mosaic images can be mapped onto the building models. This study develops a
procedure to integrate digital pictures and correctly map them to corresponding objects in
building models. The procedure first detects shadows and blocked regions in the pictures and
excludes them from subsequent process. Secondly, overlapped regions are identified using tie
points to develop mathematical relationships of target objects across pictures. The developed
mathematical models are then used to merge the pictures to generate a smooth and seamless
composite image of the target object. Finally, the mosaic image can be mapped to its
corresponding building face (wall) using pre-defined control points. The resultant building
models will have a more accurate texture and improves the reality and practicality of cyber city
implementation.
I. INTRODUCTION
The construction and applications of three-dimensional geoinformatics are among the fast
growing research topics in the fields of remote sensing and geographic information system.
Advances of computer graphics, visualization, and other information technologies further extend
3D geoinformatics into a more complex and diverse industry. In particular, the implementation
and applications of cyber city that requires comprehensive integration of remote sensing, GIS,
and information technologies, have been identified as one of the most appealing challenges in
the research and development of geoinformatics (McEachren & Krrak, 2001; Kraak, 2002).
The fundamentals of cyber city lie on the accurate establishment of 3D building models and
realistic texture mappings of model surfaces. Currently, building models are commonly
generated from aerial photos, high-resolution satellite images, and LIDAR data in conjunction
with digital terrain models (DTM). Algorithms developed for this purpose have been proposed
and achieved certain degree of success (e.g., Rau & Chen, 2003). However, because of the
restriction in sensor looking angles, these data can only provide limited texture information of
building roofs, not surrounding walls or side surfaces. To overcome this disadvantage, this
research tries to produce more complete and accurate texture mapping on 3D building models
by developing algorithms and a procedure to generate panoramic images for individual building
walls as seamlessly as possible from mosaics of digital photographs and map them to
corresponding object surfaces in models.
Because the digital photographs are usually taken at different conditions, images are of different
perspectives, brightness, contrasts, shadings, and other properties. These variations need to be
adjusted in order to integrate into a seamless mosaic. The adjustment can be categorized into
two issues: the geometric space and the color domain.
If the camera parameters are known, the geometric correction can be done using
photogrammeric models of perspective photo mapping (Huang, 2001). Another approach is to
(interactively) identify building boundaries from images to determine faces of the building and
to map corresponding texture blocks to each surface from cropped areas selected from the image
pool (Debevec, 1996; Fu 2002) or to use highly textured points as seed points to obtain
relationship between two overlapped images (Kim et al., 2003).
For realistic texture mapping from mosaics of close-range images, in addition to the geometric
correction or registration, the variations in color space of individual images also need to be
minimized. The most common approach is to use histogram match or equalization to force the
color distribution of candidate images to be with the same range of a "base image". This method
may cause serious misrendering of shadings and sometimes may produce hazy or low-contrast
results. Burt and Adelson (1983) demonstrated a multi-resolution spline for image mosaic to
address this issue. Their algorithm is capable of generating smooth image mosaic but can only
apply to an image pair a time and requires intensive computation. Consequently, this method
may not be suitable for cyber city texture mapping. For cyber city implementation, texture
mapping of 3D building models needs to react efficiently and effectively, so fast, light-weighted
mapping algorithms are preferred. The following of this paper will describe and discuss such a
mapping approach developed in this research and specifically for cyber city applications.
