International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
nent. 
T d TRUE 3D IMAGES AND THEIR APPLICATIONS 
1ount 
Z. Wang 
ani HuaZheng Geospace, Ltd, Wuhan University Science Park, Wuhan China - 
rican zheng.wang @hzgeospace.com 
at Commission V, WG V/4 
er KEYWORDS: 3D image, True 3D image, Oblique image, True orthophoto, 3D modeling, 3D city, 
Lidar, 
ca ABSTRACT: 
oring 
A true 3D image is a geo-referenced image. Besides having its radiometric information, it also has true 3D- 
tem ground coordinates XYZ for every pixels of it. For a true 3D image, especially a true 3D oblique image, it has 
true 3D coordinates not only for building roofs and/or open grounds, but also for all other visible objects on the 
ground, such as visible building walls/windows and even trees. The true 3D image breaks the 2D barrier of the 
ilable traditional orthophotos by introducing the third dimension (elevation) into the image. From a true 3D image, for 
Aarch example, people will not only be able to read a building's location (XY), but also its height (Z). true 3D images 
will fundamentally change, if not revolutionize, the way people display, look, extract, use, and represent the 
5 and geospatial information from imagery. In many areas, true 3D images can make profound impacts on the ways of 
how geospatial information is represented, how true 3D ground modeling is performed, and how the real world 
scenes are presented. This paper first gives a definition and description of a true 3D image and followed by a 
2011. brief review of what key advancements of geospatial technologies have made the creation of true 3D images 
possible. Next, the paper introduces what a true 3D image is made of. Then, the paper discusses some possible 
Me ac contributions and impacts the true 3D images can make to geospatial information fields. At the end, the paper 
mber presents a list of the benefits of having and using true 3D images and the applications of true 3D images in a 
couple of 3D city modeling projects. 
r the 
data. 
1. INTRODUCTION an orthophoto only have XY coordinates. Even we 
earth- could assign an orthophoto with the elevations or Zs 
er 20, : . 
1.1 Definitions that are used to make it, those Zs only represent either 
bare-earth ground and/or building tops. These 
pag A true 3D image is a geo-referenced image that covers orthophotos cannot correctly represent the XYZ 
sessed 
Band 
at: 
ilable 
eport. 
»matic 
a scene of ground surface. For a true 3D image, every 
pixels of it have true three dimensional coordinates 
XYZ. In other words, every objects in such a true 3D 
image, no matter how big or small they are, no matter 
they are buildings or trees, and no matter they are on 
tops or sides of objects, all have their own XYZ 
coordinates. 
1.2 Background Information 
2D geo-referenced images are widely used in GIS and 
they are called orthophotos. However, every pixels of 
199 
coordinates of objects sides, such as building sides. 
Therefore, orthophotos can at best be called 2.5D geo- 
referenced images. 
1.3 Motivations 
There are two obvious drawbacks of orthophotos. For 
an orthophoto, the first drawback is the lacking of true 
XYZ coordinates for all the pixels of it. The second 
one is that orthophotos, especially the true orthophotos 
in which all building leans have been removed, 
represent a ground scene very different from what 
people see on the ground every day. Figure 1 shows a