Texturing based on different exposure setting

From the architectural point of view, the geometries which are closer to the camera should be brighter and those which are farther should be darker. It is possible to create a very light-weighted geometry in LOD 2.5 for web- based applications such as Google Earth, Microsoft Virtual Earth and mobile navigators based on this concept to reduce the geometries and textures accordingly. To increase LoR, the geometry with lots of raised columns represented as flat rectangle geometry and the brightness of the columns are increased or for the deeper parts the brightness decreased. This is a trick which can be used for reducing the geometry and number of texture files and increase LoR as well. Fig 8: shows the concept. In the texture of the façade, the pixel values are increased for the column in left side of the texture to represent raised geometry and then the texture left-right transformed symmetrically.

Fig 8: The texture created based on Left-Right symmetrical transformation and the brightness of raised column geometries (a) and tessellated on the 3D model of the Putrajaya Prime Minister Department (b). 5.3 Texturing based on Alpha Channel

Portable Networks Graphics (PNG) introduced in 1994-1998 by (Boutell et al., 1999). PNG is a suitable image format for transmitting via network and uses lossless data compression algorithm. This format supports RGBA (Red, Green, Blue, Alpha). Alpha channel varies from 0% up to 100% which is completely transparent. This concept was employed to create lamp posts, trees, fences in front of Putrajaya corporation building, traffic lights and other street furniture. In order to reduce the heavy geometries of these objects, just cubic geometry is defined and the texture file in PNG format with transparent parts mapped on the geometry. The textures rectified and left-right transformed symmetrically and unneeded parts deleted before mapping on the geometry before converting to CityGML (See Fig 9).

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Fig 9: Statues, annexes between the departments and fence textures were created based on Alpha Chanel and mapped on the rectangle light-weighted geometry. Some of lamp posts and trees were created on tow perpendicular rectangle geometries with transparent parts intersecting each other from the middle at 90 degree

angle or three rectangles at 60 degree angle. 5.4 Texturing based on polygonal concept

(Tsai and Lin, 2006) introduced a polygon based texturing method for non-planer and irregular geometries such as semi-cylindrical and semi-elliptical shapes. Geometric distortion of this kind of façade tremendously depends on the exposure angle. It is really challenging to map such a texture either on a rectangle image frame or on the generated virtual 3D geometry. In polygonal based texture mapping a two-step adjustment were processed before registration. The approximation of top and bottom lines of the façade, processed in the first step by employing polynomial functions in order to make the curved top and bottom lines horizontal. In the second step the image stretched horizontally until the vertical lines in left and right side of the image were aligned correctly.

Fig 10:(Tsai and Lin, 2006) Two step adjustment of irregular-shaped façade image.

Where are polynomial functions, representing bottom, top, left and right sides of the frame and i, j are horizontal and vertical pixel indices respectively. MAX in equations (1) and (2) measure the maximum distance of top-bottom and right-left polynomials respectively. It is also possible to use some photo editing commercial software such as Photoshop with user-friendly toolboxes for free transformation which could be time consuming. Finally the generated texture should be mapped on the rectangle geometry which is created temporarily parallel to the curved geometry. The texture must be projected on the curved geometry from the rectangle flat geometry. The rectangle geometry which is created temporarily can be omitted after projecting the texture.

Behnam Alizadehashrafi, Alias Abdul-Rahman, Volker Coors

Fig 11: Texturing semi-elliptical building of MacGDI.

CityGML and CityServer3D

CityGML is a profile of GML3, which implements an interoperable, multifunctional, multi-scale and semantic 3D city model (Kolbe et al., 2006). Cityserver3D is a client-server DBMS (Data Base Management System), developed by Fraunhofer IGD (Germany). It can support any kind of sophisticated geometry in varying LODs based on polygons within CityGML format via MySQL (My Structure Query Language) and JVM (Java Virtual Machine). Polyhedron geometry which is supported by CityGML is sufficient to model every object such as street furniture and building in Putrajaya. CityGML format is beneficial for managing 3D city model as a multipurpose data source. External code list is a value defined by OGC for semantic modelling of objects by their type of class, function, usage, roof type, installation, material, and so on. It is a sort of indexing database and can be used for querying and analyzing for multipurpose issues. The end users may not need to know these codes but they can recognize the semantic definition of the external code list by query in the interface of CityServer3D. The operator can define different attribute for the different part of a building based on layers or components. Billboards, movies, animation and image as a standalone object are supported neither in CityGML nor in CityServer3D. There must be geometry based on polygon or polyhedron and the texture can be mapped on the geometry. Majority of the 3D virtual environments support image files as a standalone objects in any format (See Table 1) except CityGML and CityServer3D. To solve this problem the polyhedron geometry should be created and the texture must be mapped on the geometry before converting to CityGML via CityGML Plugin or FME and then can be imported to CityServer3D. Polygon and polyhedron can be converted from any 3D format to any other 3D file format without many changes in the content and the size of the file. For instance the result of converting cylinder form 3DMAX to VRML creates smaller file size than converting the same cylinder from SKP to VRML. Cylinder is defined both in VRML and 3DMAX but not in SKP so that it must be represented by lots of polygons which make a huge VRML file size. The same problem may happen while converting SKP to CityGML where polygon is the only thing that already defined. This is the main reason that CityGML files are of a huge size of text file especially for complex and sophisticated geometries. The list of nodes for each polygon in CityGML must be counter clockwise facing to the camera position so that it can be visible in CityServer3D. The solution for this problem is by making all the faces counter clockwise before converting to CityGML. Checking the 3D model in monochrome mode, can help to find those faces which are in gray colour or clockwise. These faces must be reversed or oriented before texturing and converting to CityGML (See Figure 15). An automated 3D healing model has been started (Bogdahn and Coors, 2010a) in Stuttgart University of Applied Science. The system receives original model and based on a validation and healing plan it will generate correct model automatically or create correction recommendation for the operator to heal the 3D model. Finally the system creates the quality and healing report.

SketchUp supports moving objects using Sketch Physics Plugins which is not in the field of GIS. VRML also supports moving objects like the sign of Mercedes on the top of the tower of main Station in Stuttgart which is rotating in the 3D model the same as reality (See Fig 12). In addition some of the shapes are not defined in sketchUp such as circle or sphere but they are defined in VRML. Physics engine, billboards, shapes such as arc, circle, sphere, moving objects, animations and movies are out of the scope of CityGML and CityServer3D.

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Fig 12: The sign of the Mercedes Benz is rotating the same as reality on the top of the tower in main station in our 3D model of Stuttgart in VRML.

In VRML we can use TimeSensor and OrientationInterpolator keywords in order to animate and rotate an object in

BitManagement (VRML/X3D viewer ) or VRML cortona environment. These keywords are used to rotate textured circle geometry on the top of the tower of main station in Stuttgart virtual 3D model.

The most important part of CityGML is semantic modelling within the CityServer3D and querying database on demand. Direct access to the MySQL database behind the scene of CityServer3D is possible using DDL (Data Definition Language) and DML (Data Manipulation Language) to define and manipulate the data directly, but it is not recommended. Access to the database should always be done via CityServer3D along with Java Framework. A Web3D-Service interface can be used to access the database which is rather difficult and challenging. However, this will be the best interface to access the CityServer3D database from other programs. Fraunhofer is currently preparing an OGC (Open Geospatial Consortium) experimental interoperability to test the Web3DS specification (see OGC website http://www.opengeospatial.org/standards/gml ). To change or add external code-lists for some religious landmarks such as the dome of the mosque, or the tower of the mosque for mounting the speakers on that, we need some knowledge on the implementation which could be done only in a joint project with Fraunhofer IGD. There is an error in the specification of external code-lists in CityGML 1.0; must be fixed in CityGML version 1.1. So far, the only solution is to extend existing code-lists to define semantic database for geometries such as dome of the mosque. We proposed to add the code lists developed in the Putrajaya3D project to the CityGML standard working group as an example of the recommended use of external code lists in CityGML 1.1. However, some formal issues are required. An official organization such as MaCGDI together with our 3D GIS RESEARCH LAB members in UTM should be in charge of supporting and maintaining these code lists and make them public available. The data management component in Google Earth is file based such as KML files that are not feasible for large models and done by Google with their own 3D geo- special database. With CityServer3D, data management is in control of MaCGDI and UTM. The size of the 3D models in Google Earth is restricted and normally is in LOD2.5 along with textures for each object but in CityServer3D buildings in LOD4 such as MaCGDI can be imported along with semantic data.

Behnam Alizadehashrafi, Alias Abdul-Rahman, Volker Coors

Table 1: Represents the defined shapes in different 3D environments Shapes\3D

environment

VRML97 SketchUP 3DMAX CityGML

Circle √ √

Sphere √ √

Cone and Cylinder √ √

Arc √ √

Polygon √ √ √ √

Animation √ √ using Sketch Physics Plugins

√

Billboard √ √ √

Image as a

standalone object √ √ √

Converting models which include shapes such as circle, or moving and dynamic geometries from VRML to 3DS, using 3DMAX, encounters errors (See Fig 13). The only way to solve this problem is to delete that part of the VRML code before converting to CityGML (See Fig 12 and related code which should be omitted before converting). These shapes are represented as a smooth polygon in other 3D formats such as SKP (See Table 1). X3D and M3G support movies within the virtual 3D environment on the virtual display which is not supported by CityServer3D. Fig 14 shows some of the problems of converting billboard and images as a standalone object to CityGML.

Fig 14: A billboard and a standalone image were converted to CityGML. The image was lost and the billboard became a fixed object which is not facing to the camera.

Fig 15: Two faces of C26 in UTM are in grey color in monochrome mode (a). After converting to CityGML these faces are invisible from outside as they are not oriented (b). This problem was solved in (c) after reversing

and retexturing.

Visualization of the name or label of the building while hovering the mouse on the 3D model or navigating within the cityServer3D is not supported as well.

SketchUp is using WGS84 coordinate system. After converting the model to CityGML using CityGML-Plugin in Google SketchUp the model was not geo-referenced in previous version. This problem was fixed in the newer version of the CityGML-Plugin which can be downloaded from CityGML webpage.

The terrain and Ortho-photo from Putrajaya Prime Minister Department to Putrajaya International Conventional Centre about 5 kilometres by one kilometre created using Google terrain with the grid size of 76 meter. 25 buildings, 4 bridges and all the street furniture such as spot lights, lamp posts, trees, and traffic lights were modelled and textured by aforementioned methods in this area along with semantic data in CityServer3D(See Fig: 16, 17).

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Fig 16: 3D model of Putrajaya from PICC to PPMD along with semantic data in CityServer 3D.

Figure 17: