Tips, Tricks Guidelines around data import

Georeferencing and Coordinate Systems

Proper georeferencing is essential for integrating architectural models into digital twin environments. The most common challenges arise when converting local CAD coordinates to world coordinate systems.

Common Georeferencing Challenges

CAD Paper Space Issues

Architectural drawings often use CAD paper space layouts that create multiple coordinate system problems:

Multiple coordinate origins: Paper space can have different origins than model space, causing positional offsets
Scale variations: Paper space scaling factors may not represent real-world dimensions
Rotation discrepancies: Drawing orientation in paper space may differ from true north orientation
Unit inconsistencies: Mixed units between paper space (often inches or points) and model space (meters/feet)

Always work from model space coordinates when extracting geometric data from CAD files.

Local vs. Global Coordinate Systems

Architects typically work in local coordinate systems that need transformation to global systems:

Arbitrary origins: Buildings are often modeled with convenient local origins (e.g., building corner at 0,0,0)
Missing elevation data: Ground level elevation relative to sea level is frequently undefined
Orientation issues: Building orientation may not align with true north or grid north

Correctly georeferenced models with a known/defined coordinate system will be reprojected to a local/common coordinate system where the models centre point is at 0,0.

For IFC models to correctly get placed, the model needs to have properly set the IfcMapConversion and IfcProjectedCRS elements. Without these a fallback will be done by using the Latitude and Longitude defined in the IFCSite feature.

Best Practices for Architects

CAD File Preparation

Work in model space: Ensure all geometry is created in model space coordinates
Use consistent units: Maintain uniform units throughout the model (preferably meters)
Include site context: Model buildings in relation to site boundaries and nearby features
Document coordinate system: Clearly specify the coordinate system and datum used

Troubleshooting Common Issues

Positional Offsets

Problem: Model appears in wrong location after import or the model is not visible

Solutions:

Check for paper space vs. model space confusion in original CAD file
- A check of the model is done on the extent of the model, if the model is more than 10,000 meters (10km) from the models coordinate origin (0,0) in both the x and y direction the model will be shifted back to 0,0 and should appear at the click for unprojected models. If the model is less than 10km from the origin then the model will not get shifted, in this case the model can be far away from the click location.
try to place model on terrain using the VC Planner option - this can fix any issues which are caused by a mismatch in the vertical (z) origin.
try to scale the model up - it is assumed that the units of a model are in meters, however, in some cases models are incorrectly labelled as centimetres (or millimetres) and can end up getting scaled down by a factor of 100 or 1000 rendering the model almost invisible.

Scale Discrepancies

Problem: Model appears too large or too small

Solutions:

Check for scale factors in CAD drawings
Ensure consistent units between CAD and digital twin platform
Use the VC Planner’s scaling tools to adjust model size

Orientation Errors

Problem: Model is rotated incorrectly

Solutions:

Confirm true north vs. grid north vs. arbitrary north
Check for coordinate system rotation parameters
Use the VC Planner’s rotation tools to align model orientation

Elevation Issues

Problem: Model appears above or below ground level

Solutions:

Verify elevation datum consistency
Check for relative vs. absolute elevation values
Confirm ground level elevation in both coordinate systems
Use the VC Planner’s elevation adjustment tools to set model height

VC Planner Fallback

If the model cannot be georeferenced correctly, the VC Planner provides a fallback mechanism to manually adjust the model position, scale, and orientation within the platform. This allows for quick corrections without needing to re-export the model from CAD software.

Unreferenced Models Workflow by using the VC Planner (extended)

When working with unreferenced models in the VC Planner, follow these steps to ensure proper integration and visualization:

Importing projected Models without known Reference system

Explanation: Some formats such as OBJ, DXF, or DWG do not contain information about the coordinate system, but the coordinates are in the world coordinate system (i.e., they are projected). These models must be manually assigned a reference system to be correctly placed in the VC Planner. A WKT (Well-Known Text) file defines the coordinate system in which the model was originally created.

Procedure:

Create a ZIP file
Include the 3D model file: Ensure the model is in a supported format (e.g., OBJ, DXF, DWG, etc.)

Add a metadata file: Create a {3dmodelfilename}.prj file (having the same filename as the 3D model + the extension prj) providing the following information: + the WKT (Well-Known Text) representation of the model’s coordinate system + like this example for ETRS89 UTM Zone 32N:

PROJCS["ETRS_1989_UTM_Zone_32N",GEOGCS["GCS_ETRS_1989",DATUM["D_ETRS_1989",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",9.0],PARAMETER["Scale_Factor",0.9996],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

Upload the ZIP file: Use the VC Planner’s import functionality to upload the ZIP file containing the model and the metadata file
Verify model position: After import, check the model’s position in the 3D view to ensure it aligns with the expected location based on the provided coordinate system
Adjust if necessary: If the model does not appear correctly, use the VC Planner’s tools to manually adjust the position, scale, and orientation as needed

WKT files are a standard way to define coordinate systems and can be generated by most GIS software. Ensure the WKT string is accurate to avoid misalignment issues. WKT files can be found here: https://epsg.io/ or https://spatialreference.org/

Importing Models without Reference system located at 0,0 point

Explanation: Some models do not have a defined coordinate system and are located at the origin (0,0). These models can be imported with a simple metadata file that defines their position relative to the world coordinate system.

Procedure:

Create a ZIP file
Include the 3D model file: Ensure the model is in a supported format (e.g., OBJ, DXF, DWG, etc.)

Add a metadata file: ReferencePoint.json with the following content:

{
	"heading": 0,
	"height": 100,
	"latitude": 45,
	"longitude": 45,
	"pitch": 0,
	"roll": 0,
	"scale": 0
}

Parameter	Value	Description
heading	0	Rotation around the negative z-axis in degrees
height	100	Height of the model above ground level in meters
latitude	45	Latitude coordinate of the model’s reference point in degrees (WGS84)
longitude	45	Longitude coordinate of the model’s reference point in degrees (WGS84)
pitch	0	Rotation around the negative y-axis in degrees
roll	0	Rotation around the positive x-axis in degrees
scale	0	Scale factor for the model (1 = original size, >1 = larger, <1 = smaller)

Parameter

Value

Description

heading

Rotation around the negative z-axis in degrees

height

100

Height of the model above ground level in meters

latitude

Latitude coordinate of the model’s reference point in degrees (WGS84)

longitude

Longitude coordinate of the model’s reference point in degrees (WGS84)

pitch

Rotation around the negative y-axis in degrees

roll

Rotation around the positive x-axis in degrees

scale

Scale factor for the model (1 = original size, >1 = larger, <1 = smaller)

Upload the ZIP file: Use the VC Planner’s import functionality to upload the ZIP file containing the model and the metadata file
Verify model position: After import, check the model’s position in the 3D view to ensure it aligns with the expected location at the origin (0,0)
Adjust if necessary: If the model does not appear correctly, use the VC Planner’s tools to manually adjust the position, scale, and orientation as needed

3D Model Optimization

When uploading 3D models for browser-based visualization in urban digital twins, performance optimization is crucial. Here are essential guidelines to ensure smooth rendering and navigation:

Building Models Guidelines

Exterior Optimization

Remove interior details: Strip all internal walls, furniture, fixtures, and room divisions that won’t be visible from outside
Simplify building shells: Focus only on the outer envelope - external walls, roof, and major architectural features
Optimize facade details: Reduce complex architectural elements to essential visual features that maintain recognizability
Use texture mapping: Replace detailed geometry with high-quality textures for surface details like brick patterns, windows, or decorative elements

Geometric Simplification

Reduce polygon count: Aim for reducing the polygons as much as possible
Eliminate hidden faces: Remove polygons that face inward or are completely occluded
Merge coplanar surfaces: Combine adjacent flat surfaces into single polygons where possible

General 3D Asset Guidelines

File Formats and Compression

Texture compression: Apply JPEG compression for color textures, PNG for transparency
Texture resolution: Limit to 1024x1024 pixels for most buildings, 2048x2048 only for landmark structures
Model compression: Use Draco compression for geometry when available

Performance Considerations

Batching similar objects: Group identical elements (trees, street furniture, etc.) to reduce draw calls
Instancing: Use instanced rendering for repetitive elements like windows, balconies, or vegetation
Culling preparation: Ensure models are properly oriented and positioned for frustum culling
Material optimization: Minimize unique materials - reuse and share materials across multiple objects

Quality vs Performance Balance

Visual Fidelity Guidelines

Maintain silhouette accuracy: Preserve the recognizable outline and major proportions of buildings
Key architectural features: Retain distinctive elements that aid in navigation and recognition
Material variety: Use sufficient material variation to distinguish between different building types
Lighting considerations: Ensure models work well with dynamic lighting and shadows

Technical Specifications

Memory constraints: Keep individual models under 10MB, total scene under 100MB loaded
Mobile compatibility: Test performance on mobile devices with limited GPU capabilities
Browser limitations: Consider WebGL constraints and varying browser performance

Workflow Recommendations

Pre-processing Steps

Audit original models: Identify and catalog all unnecessary elements before optimization
Establish naming conventions: Use consistent naming for materials, textures, and model hierarchies
Version control: Maintain both original high-detail and optimized versions

Quality Assurance

Performance testing: Regularly test loading times and frame rates during development
Visual validation: Compare optimized models against originals to ensure acceptable quality loss
Cross-platform testing: Verify performance across different devices and browsers
User feedback integration: Collect and incorporate user experience feedback on navigation and visual quality

Start with aggressive optimization and gradually add detail back where needed, rather than trying to remove detail from complex models.