iModel Display Extents represents a bounding box or the volume of interest of the iModel's coordinate system, and all geometry of an iModel must be contained within such limits. Individual iModels can have separate extents within an iTwin.
Image 1 - iModel with shown Extents
In this manner, multiple iModels can be oriented relative to one another and relative to external reality models, cartographic and geographic information systems, etc.
While there typically are no hard limits imposed on the size of the Extents, we would recommend not exceeding these maximums:
- For the height of the Extents, the recommended maximum is 2 km.
- For the length and width of the Extents, the recommended maximum when a GCS is defined is 350 km and 20 km for iModels that are not map projections (only ECEF transform defined).
Please refer to the individual product documentation to determine if any limitations are imposed.
Table of Contents
Set the Extents
When you create an iModel in various Bentley products, you might have seen functionality to define Maximum Extents as 2D rectangle. We always recommend setting those up, as this will optimize viewing performance, making elements outside the interest area not shown. Refer to the Potential data issues chapter to learn more.
Image 1 - Maximum Extents example in ProjectWise 365
If you synchronize files using iTwin Connectors, the actual Extents will be statistically determined based on your data (as long as it is within the defined Maximum Extent area), and it could be smaller than the area you set up as Maximum Extents. In subsequential synchronizations, when a lot of new data is found, the original Extents might be adjusted to cover the probable new interest area.
Image 2 - Extents determined by iTwin Connectors
If iTwin Extents were set or adjusted manually, the iTwin Connectors will always honor those values and will not modify them further independently of your actual data.
Visualize the Extents
Please refer to the individual product documentation to determine if and where such Extents functionality is exposed in the interface. For example, in some viewers, that might be under Diagnostic Tools, as shown in an image, or as part of the Geospatial Metadata panel widget.
Image 3 - Extents exposed in Design Review
For developer resources, you can find more documentation on the iTwin.js iModels overview page or try the "Visualize Project Extents" sandbox.
Image 4 - Visualize Project Extents sandbox
Potential data issues
There are cases where the result is not as expected after synchronizing BIM files to an iModel. Examples:
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Source models had very distant elements
Your design file may have contained a few elements far from the model's origin. In such a case, you would not see them in iTwin-based viewers by default, as they would be outside of Extents. iTwin Connectors would identify statistically outlying elements. Such issues would be exposed in the Synchronization Report interface as errors:
Depending on your needs and practices, you should update the source files to place such elements correctly or delete them.
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Partially visible data on iModel
There could be different reasons if you notice missing models when visualizing the data.
- If the whole model is not visible, it is possible that the source file was in a distant location or had a wrong geographical coordinate system. You may need to apply a transform to place it correctly or change the origin or coordinates in the file so that it comes into the correct location when synchronized.
- If some data from iModel looks like 'cut,' it is possible that the wrong spatial root file was specified, resulting in false original Extents values. You may need to adjust the Extents to match the boundary of the project as needed.
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Image 5 - Partially visible iModel |
Image 6 - Models or all iModel is outside of Extents |
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iModel is in the wrong location
If iModel is in the wrong location, adjusting Extents will not move the iModel itself. You need to update the source files to place data correctly. You can find best practice guides on bringing spatially aligned data to an iTwin here.
Change the Extents
We are researching the requirements for iTwin Realignment Tooling, which could help adjust iTwin Extents and move iModel or individual models into correct locations if that can not be done by editing the source files with design applications. If you are interested in participating in such research or providing feedback in usability lab sessions, please fill out this form: https://forms.office.com/r/FBY5FYSy1n, and we will contact you with more details.
Synchronization Report
After bringing the data to an iTwin, it is worth checking iModel synchronization report to inspect any potential issues. Here are examples of issues that iTwin Connectors could report and how best to fix it.
iModel Display Extents volume issues
If any of the issues listed below are shown in the Synchronization Report, there are issues with your current data. As a result, the Extents volume could not be appropriately supported and will affect display performance.
Image 7 - Extents volume issues
Potential errors:
- Error message: Project extents are too tall: <value> meters (expected less than 900 meters). Element geometry this expansive will affect display performance and often indicates corrupt elements or transforms.
- Error message: Project extents are too low: <value> meters (expected greater than 11000 meters). Element geometry this expansive will affect display performance and often indicates corrupt elements or transforms.
- Error message: Project extents are too high: <values> meters (expected plane dimension less than 9000000). Element geometry this expansive will affect display performance, and often indicates corrupt elements or transforms.
- Error message: Project extents are too high: <values> meters (expected less than 8850 meters). Element geometry this expansive will affect display performance, and often indicates corrupt elements or transforms.
- Error message: Project extents are too narrow: <values> (ratio of largest footprint dimension to height; expected greater than 0.10). Element geometry this expansive will affect display performance, and often indicates corrupt elements or transforms.
- Error/Warning message: Calculated extents along z is too big <value> x <value> = <value> m. Clamping it to <value>x<value>
- Error message: Element '' is excluded due to invalid extents: too small height 0.00 mm. Please try to re-publish this Review file from original source again.
Solution:
- Check Design Elements: Update the source files to correctly place or delete elements depending on your needs and practices.
- Review GCS Systems: Ensure identical GCS systems are defined in the source files. Fix any inconsistencies. Each design application will have specific information about setting and using GCS data. You can find more information in the iTwin Spatial Alignment articles or directly in design applications documentation. In the case of dgn files, file referencing support could be used as a technique to locate incompatible files.
Issues with reprojecting data
If there are any issues with reprojecting design data from one geographical coordinate system to another, or some data was reprojected since several of your files contained a different coordinate system than the one used for iModel, as a result potential messages would be shown:
- Warning message: Geo-location point (Survey Point 0.000, 0.000) was moved to local zero coordinate (Project Base Point <values>) due to too large distance 5822 km between them to provide more accurate elements placement. But it's better to follow suggestions from Autodesk to fix this right in the source file: http://help.autodesk.com/view/RVT/2018/ENU/?guid=GUID-3F79BF5A-F051-49F3-951E-D3E86F51BECC
- Informational message: The file was published without geo-coordinates reprojection. Its Survey Point got <coordinates> coordinates instead of <coordinates> with reprojection usage.
- Informational message: This file was reprojected to <coordinates> from the original location <coordinates> in WGS84 <coordinates> geo-coordinates at <coordinates>.
Elements were excluded from the Extents
As described in the previous chapter about potential data issues due to data modeling issues several informational, warning, or error messages could be shown. Depending on your needs and practices, you should update the source files to place such elements correctly or delete them.
Potential errors:
- Error message: Element(s) were considered statistical outliers and were excluded from the project extents. They may not be visible in this project. This often indicates corrupt elements or transforms.
- Informational message: <Count> Outlying elements were ignored when calculating project extents.
- Informational message: In ModelName: <model name> elements out of range < [Element_Name,Element_Id]>.
- Informational message: In ModelName: <model name> and FileName: <file name> elements out of range < [Element_Name,Element_Id]>.
Solution:
- Check Design Elements: Some elements in the synchronized data are outside the viewable range for an iModel. Update the source files to correctly place or delete elements depending on your needs and practices. For example you could identify those outliers if you enable the iModel Display Extents in your viewer, or you can see those listed in the Geospatial Metadata widget warnings section.
- Define Maximum Extents if needed: If you can't fix the input data, use this guide on creating an iModel that will help constrain the iModel extents.
- Adjust the iModel Display Extents: if non visible elements are required you can adjust the iModel Displat Extents. [Coming Up]
- Synchronize Files in the Correct Order:
- For Reality Data: Synchronize with a defined GCS first, a DGN with an identical GCS second, followed by other models.
- For non-DGN files: Synchronize a DGN with a defined GCS first, followed by non-DGN models next.
- For files without a GCS defined: Synchronize a DGN with a defined GCS first, followed by models with an undefined GCS next.
- Review GCS Systems: Ensure there are identical GCS systems in the source files. Fix any inconsistencies. Each design application will have specific information about setting and using GCS data. You can find more information in the iTwin Spatial Alignment articles or directly in design applications documentation. In the case of dgn files, file referencing support could be used as a technique to locate incompatible files.
iModel Display Extents have been adjusted
Potential errors:
- Error message: Project Extents have been adjusted to exclude outlying elements - Element Id: <element ID>, Model Name: <model name>, File Name: <file name>.
The site is located too far from the coordinate system origin
The iModel location and GCS origin distance must be within the normal range (16KM) so the model location will be correct.
Potential errors:
- Error message: Failed to convert [Error: Geometry in the published model is too far away from the origin, please keep your elements centered around the design file origin].
- Warning message: Site located (336.607,5779.87,0.002666) km from coordinate system origin. It is too far and globe placement may be inaccurate. Consider re-creating the input file with better positioning.
Solution:
- Correct the Design Data: Such issues are always related to the source data. iTwin Spatial Alignment articles will help you validate data positioning and make required changes to design applications based on your data type. Once the file is corrected, re-synchronize the file into the iModel.
- Contact Bentley Support for assistance if these issues cannot be solved.