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AUTOMATIC 3D RENDERING OF HIGH RESOLUTION SPACE IMAGES m 
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C. Destruel *, C. Valorge® 
* CS-SI, Rue de Brindejonc des Moulinais BP5872 - 31506 Toulouse Cedex 5 - France 
? CNES, DSO/OT/QTIS/HR, 18, av. Belin — 31401 Toulouse Cedex 4 — France 
Commission V, WG V/6 
b KEY WORDS: High resolution, 3D models, visualization, virtual reality, Pléiades 
ABSTRACT: 
  
Virtual flights over a Digital Surface Model (DSM) textured with an image are now widely used for communication purposes 
1 towards the general public, decision-makers and non-specialists in general. Furthermore, recent advances in computer science and 
| virtual reality make very easy to perform such flights, even on a standard laptop. Examples will be given with SPOTS 2.5m colour 
i images applied to HRS-derived DSM on a 60 km by 60 km surface. The r 
i Performing the same kind of virtual flight over metric images needs to solve a certain number of problems related to the fact that we the ot 
i have to move from a 2.5D description of the landscape to a real 3D description, essential for the recognition of all the objects that 
n 1 . . ~ > . . ~ . . 
can be seen in such images. Therefore, the surface can no longer be described as a regular grid of altitudes, especially to be able to 
account for vertical walls. [t is necessary to use a vectorized description of the landscape geometry, for example an irregular network 
of triangles (TIN) in a Virtual Reality Mark-up Language (VRML) format. 3.1.1 
| The problem of estimating a 3D model from images will not be addressed here. For our purposes, we will consider that this 3D : 
geometric description is available from other sources (city models...) and that we “only” want to be able to virtually generate the The 1 
| landscape by applying a metric image over a given 3D model. textur 
| In this case, the first step is to check its quality and eventually simplify the 3D model -its quality and level of detail can vary such 
| considerably from one source to another, even for a same town- and then to merge it with a traditional Digital Terrain Model, giving eleme 
the altitude of the ground and of the object's bases. durin 
The second step consists in registering the image with the geometric model with a sub-pixel accuracy. RM 
The third step deals with the texturing of the geometric model with the image, which means associating each triangle with the image 
chip representing its radiometry. This extraction process must take into account the viewing angle of the surface in the image and its 
à orthogonal projection. 
At this level, we have produced a virtual mock-up modelling a real 3D landscape that we can use to generate several outputs: an 
i image in any projection (an ortho-image, for instance), any perspective view of the landscape or a virtual flight. 
| We will illustrate the different stages of the processing with Pléiades-HR simulated images texturing the 3D model of Toulouse. 
1 1. INTRODUCTION 
I Nowadays, advances in Earth Observation allow the layout of 
big databases using high-resolution images (Valorge, 2003). 
Images taken from Space are now commonly used in 
    
J presentation or demonstration applications, no longer reserved Takin 
J to professionals but also intended to neophytes. Among these Figur 
Ü applications, one can note the significant place of software make: 
À presenting these data by using Virtual Reality metaphors. the w 
: In Virtual Reality, the use of teledetection data implies the faithf 
| knowledge of the landscape (and not only of the image) on Consi 
| which the user wishes to fly. Even if navigations using a Digital : 
a Elevation Model (DEM) as geometric base are now widespread, Furth 
: the increase in image resolution asks for using a true 3D be us 
1 geometric data set instead of a classic 2.5D DEM. » dii 
à 2. 2,5D NAVIGATION Figure 1. Virtual navigation over SPOTS data 32 
Now it is quite common to see and handle 3D virtual A classic navigation scenario (Vadon, 2003) is composed of a Diffe 
navigations on a DEM textured with satellite images (Appleton, 60km x 60km area made up of 20 or 50 meter resolution DEM 5 
n 2001), even if this remains a difficult exercise to ensure a anda color image of 2,5 meter resolution (see Figure 1). 
f sufficient frame rate (Zhao. 2001). One can easily realize that taking into account the geometrical . 
j Our software, VirtualGeo, makes it possible to fly over any models made up of DEM is not enough to represent the 3D Sever 
| SPOTS scene in real time and without any constraint. objects that the user perceives on a high resolution image. The not ti