OSM-4D/Generic textures

This page contains description of the concept of possible generic textures for 3D city models from the page: OSM-4D. For foto textures library see [1]

Description

The real time rendering of big 3D city models with terrain model is difficult. There are use cases for which a photo texture is not necessary. For easy rendering of big areas are scheduled small textures with 64x64 Pixel. These textures have free RGB background and one of more faces einem ("doors" and "windows" representation) with other RGB value.

The textures should be used only for building facades in a lower "level of detail" LOD 1 and 2 for 3D city models.

The low resolution texture should facilitate the real-time rendering of 3D city models.

Of course, this method of representation can not show the architectural details, but it is suitable for widespread texturing of generalized city models for online - rendering.

64x64 Raster:construction grid for a texture

This method of texturing is  not for fotorealistic representation designed! 

Textures of this type should only show number of floors of the buildings and provide a rough orientation and recognition of the spatial situation.

Pros:

• Easily true-time rendering of 3D cities.
• Standardization of generic textures for 3D City Models
• Uniform naming system of the generic texture library: The entire texture library is small
• It allows faster texturing of large areas

Phototexturing vs. low resolution texturing

High resolution, unique textures or repeatable textures (Fototextur) look a lot better. Of course, this textures should gradually be used in all 3D buildings. But you must know about the difficulties of the high resolution texturing:

• High labor costs. For generating of unique textures each building must be photographed from each side. You get the best texture when you shot frontal photograph of each facade. These photos will then be processed (equalizing,matching).

• Expertise required. Die Fotos müssen in der Farbigkeit aneinander angepaßt werden. Autos, Bäume, Menschen, Straßenlaternen und ander störende Elemente müssen von den Bilder entfert werden. Dies ist nicht immer möglich, wenn z.B. Bäume fast die gesamte Fassade verdecken. Die Texturränder müssen wiederholbar "seamless" sein. Die Texturauflösung muß aneinander angepaßt werden.

• Naming. Bei vielen Usern und vielen Fototexturen wird schnell eine große Anzahl von großen Texturen entstehen. Entweder findet man dafür eine Lösung, die Texturen miteinander vergleicht und sortiert, oder es wird viele fast identische Texturen mit verschiedenen Namen geben. Auch gleiche Namen für verschiedene Texturen können zu Problemen führen.

• Error prone technique. Schlechte Skalierung der Texturen bzw. schlechte Platzierung passieren selbst den Profis relativ oft.

• Real-time visualization. The amount of data that will result from photo textures is relatively large. Either one is developed mechanisms that provide texture optimization, or the real-time rendering will be difficult.

Despite these difficulties, it is obviously that the future belongs to fototexturierung:

Die Modelle sehen wesentlich interessanter aus, haben einen höheren Wiedererkennungswert und beinhalten wertvolle Zusatzinformationen.

Tagging

Idea:

Syntax

The texture name is also the unique description of the texture and consists of integers.

The texture with syntax ABCDEFGH consists of:

AB = x Coordinate of the beginning of the color which symbolizes the opening (dark blue). The smallest possible value is 00, the largest 63

CD = y Koordinate von dem Anfang der Farbe welche die Öffnung symbolisiert (dark blue). The smallest possible value is 00, the largest 63

EF = x Koordinate von dem Ende der Farbe welche die Öffnung symbolisiert (dark blue). The smallest possible value is 01, the largest 64

GH = y Koordinate von dem Ende der Farbe welche die Öffnung symbolisiert (dark blue). The smallest possible value is 01, the largest 64

AB = v1

CD = v2

EF = v3

GH = v4

Weitere Elemente im Bild erhalten nach einem Unterstrich entsprechend die Syntax: A´B´C´D´E´F´G´H´

Analog: Eine Textur, die n Flächen beinhaltet, wird beschrieben durch:

ABCDEFGH_A´B´C´D´E´F´G´H´_ ... AnBnCnDnEnFnGnHn

Examples

Key	Description	Example values	Notes
generic_texture	puts generic texture on plane	yes
texture_rotation	rotation of texture on plane in [°]	45°
scale_x	Scaling factor along the x-axis in [%]	50%
Scale_y	Scaling factor along the y-axis in [%]	74%
texturestart_x	Beginning of texture along the x-axis in [%]	0%	see part: texture moving
texturestart_y	Beginning of texture along the y-axis in [%]	20%	see part: texture moving
RGB_background	RGB value of background	250,240,230	min:0, max:255
RGB_opening	RGB value of "opening"	0,15,115	min:0, max:255

Texture name	Graphic representation
20202424
20221127_333221127
38000857
10001945_33222223
06171845_21004045_44175645
20221127_333221127
20173041_32174241_20433053_32434253
Long texture name	Lot of elements possible
01011808_20013708_ 39015608_58016308_ 01091832_20093732_ 39095632_58096332_ 01341839_20343739_ 39345639_58346339_ 01411858_20413758_ 39415658_58416358_ 01591863_20593763_ 39595663_58596363
23292435_24272537_ 25262538_26252739_ 27242930_29233541_ 35243740_37253839_ 38263938_39274037_ 40294135

Die Texturen aus der obigen Tabelle wurden gezeichnet mit den Farben:

- RGB Wert Hintergrund: 250,240,230

- RGB Wert Öffnungen: 0,20,120

Shifting of the texture

The texture usually starts in the lower left corner of the surface that is textured (insertion point). Sometimes it is advantageous if the insertion point of the texture is not at the beginning of a surface:

This texture is repeated six times along the x and 3 times along the y axis:

Result:

Texturing of surfaces with more textures

Often it is impossible to make a good surface representation with only one texture. In this case it is necessary to divide the surface in smaller areas. Each of this areas gets a separate texture.

For example: this result

can be arrive by dividing of main surface: