Texturing the facades of LOD2 City-GML Datasets using LOD3 Datasets as a reference

This is a step-by-step tutorial on how to texture facades on LoD2 City GML datasets using LoD3 datasets as a reference.

Preliminary

Texturing the facades of LOD2 City-GML Datasets using LOD3 Datasets as a reference

This is a step-by-step tutorial on how to texture facades on LoD2 City GML datasets using LoD3 datasets as a reference.

Preliminary

Required Software

• Sketch-Up with City-Editor Plug-In installed
• Basic image editing software (Microsoft Paint is sufficient)

Input Data Requirements

• Facade photographs of the target building
  • Ideally taken with a wide-angle lens
  • As orthogonal as possible to minimize distortion
• LOD2 and LOD3 CityGML Datasets
  • TUM-Data available from: Awesome CityGML Germany Repository

Data Preparation

Before beginning the texturing process, it’s important to address privacy concerns in your facade photographs. If people or belongings appear in your material you will need to either ask permission to use the data or remove everything that can be traced back to someone. The latter task can be performed using software like Microsoft Paint.:

• Black out street-level details
• Blur any visible license plates
• Blur all faces of people

Proceed, only after making sure everything is the way it is supposed to be!

Step-by-Step Process

1. Importing LOD2 Data

1. Launch SketchUp and select a simple scene

2. In the toolbar, click “Launch CityEditorImporter”

3. When the CityEditor window appears:

• Choose “add building data source”

• Navigate to your CityGML LOD2 dataset
• Select your target building

Import Settings

• In the LOD-Filter section:
  • Enable the “highest” checkbox

• Maintain default settings as shown in reference images
• For coordinates:
  • Keep all default settings
  • Ensure “automatic model origin selection” is enabled

Navigation Tips:

• Rotate view: Hold mousewheel
• Pan view: Hold Shift + mousewheel

2. LOD3 Data Integration

Before proceeding you should take notice on how big your LoD3-model is. For small buildings you could use just use the CityEditorImporter and repeat the process using the corresponding LoD3 Data… use the same settings as in the LoD2 version. The two datasets should be aligned, because they are georeferenced. However, the import using this method takes a lot of time. An alternative way, which is definitely faster, but might lead to a slightly reduced accuracy is to manually align the LoD3 building to the LoD2.

For Small Buildings:

• Use CityEditorImporter method:
  • Follow the same import process as LOD2
  • Use identical settings
  • Datasets will align automatically due to georeference

For Larger Buildings (Alternative Method):

1. Open a new SketchUp instance
2. Use SketchUp’s native file import
3. Copy the LOD3 building (Ctrl + C)
4. Paste into the LOD2 instance
5. Align datasets manually:
   • IMPORTANT: Adjust LOD3 to match LOD2, not vice versa

• Use move and rotate tools for precise alignment

• Toggle visibility using the eye button when needed

3. Texturing Process

1. Select LOD2 data:
   • Single left-click
   • Right-click > Edit group

2. Import facade images:
   • Choose starting polygon/side

• Import as Texture

• Click and drag to size
• Click to confirm

3. Orthogonalize the texture:
   • Select polygon only (the polygon should be highlighted in yellow dots)
   • Right-click > Texture > Position
   • Use pins for adjustment:
     • White pins: Align homologous points

• Colored pins: Stretch, shear, move, rotate

• Use LOD3 windows as reference points

4. Texture Optimization:
   • For repeated sections:
     • Open materials panel
     • Use sample paint tool
     • Apply to similar polygons
   • Right-click > Make unique texture
     • Reduces data size
     • Prevents texture ambiguities

4. Export Process

Only do this step when all the previous steps are done successfully and every texture is made unique!

1. Remove LOD3 dataset
2. Click CityGML export in toolbar

3. Export settings:
   • Use original building name
   • Verify texture settings

4. Complete export

Best Practices

• Maintain vertical alignment of buildings
• Double-check texture alignment with LOD3 reference
• Create unique textures for each face
• Verify export settings before finalizing

Troubleshooting

• If alignment is difficult, toggle LOD3 visibility
• For texture positioning issues, try both pin types
• Save work frequently during the process
• Verify all faces are properly textured before export