When you change your site's Coordinate Reference System (CRS), your surveys, designs, or files uploaded before the change might appear shifted or show incorrect elevations. This article explains why these shifts happen and what you can do to fix it.
Why do my surveys and designs appear shifted after a CRS change?
This comes down to two things: a visual (lens) mismatch and a vertical (geodetic) difference.
The visual (lens) mismatch
In Propeller, two coordinate settings determine how your data is displayed:
- Your site CRS: the "lens" through which the platform views all data
- Your dataset's processing CRS: the coordinate system used to process that dataset at upload
| đź’ˇTip: For a dataset to display correctly, your site CRS must match your dataset's processing CRS. |
Normally, these match automatically. But if you change your site CRS, older datasets still retain their original processing CRS.
When you view these older datasets through the new "lens" you may see:
- Elevation differences: heights may appear off by several meters (or more)
- Horizontal shifts: features may appear slightly displaced from their true location
| ℹ️ Note: The dataset itself has not moved or changed. You are simply viewing data that was processed in one coordinate system through the lens of a different one. |
The vertical (geodetic) difference
Elevation shifts happen because published coordinate systems and local grids handle vertical data differently.
Propeller uses three key geodetic values:
- Orthometric height (H): height above mean sea level (e.g., AHD)
- Ellipsoidal height (h): height above the Earth's reference ellipsoid (WGS84)
- Geoid separation (N): the distance between the ellipsoid and the geoid
| These are related by the formula: H = h - N |
In short:
- Published CRSs already apply a geoid model (N) during processing, so the platform expects orthometric heights (H).
- Local grids often use raw ellipsoidal heights (h)
If a dataset processed one way is viewed through a lens expecting the other, the N step is added or omitted incorrectly; causing a visible jump, often around the value of N (e.g., 20–30 m).
| ℹ️ Note: A “geoid model” converts ellipsoidal height to mean sea level height. Differences between models cause apparent vertical shifts. |
When does this problem happen?
CRS mismatch affects:
- Survey datasets
- Design surface files
- Point clouds and other geo-referenced data uploaded before a CRS change
The shift is most noticeable when:
Switching between a published CRS (e.g., GDA2020 / MGA Zone 56) and a local grid
Switching between coordinate systems that use different vertical datums or geoid models
How do I check if my dataset CRS matches my site CRS?
Check your dataset CRS:Â
When viewing a survey dataset, you can always check what CRS it was processed in by navigating to the Processing Report (go to Outputs → Processing Report)
Check your site CRS:
Click on the geolocation banner in the bottom-right corner of the platform.
| ℹ️ Note: If these two coordinate systems differ, you will likely experience the elevation or position shifts described above. |
How can I correct the CRS mismatch?
| đź’ˇTip: For best practice, always set your site CRS correctly before uploading any data. This ensures all datasets are processed consistently. |
If you have already changed your site CRS and are seeing shifted data, try one of these options below.
Option 1: Reupload and reprocess affected surveys and designs
The most reliable fix.
- Identify the surveys and designs uploaded before the CRS change.
- Reupload the raw data to your site.
- Propeller will process the new assets using your current site CRS, and they will then align properly.
| đź’ˇTip: Use this option whenever possible for highest accuracy. |
Option 2: Temporarily switch your site CRS back
If you need to view older datasets in their original alignment, you can temporarily revert your site CRS to the old one.
- Keep in mind: New datasets processed in the current CRS will then appear shifted until you switch back.
Option 3: Use caution when measuring across CRSs
If you must work with datasets processed in different coordinate systems:
- Elevation measurements may be inaccurate.
- Volume calculations may produce incorrect results.
- Design overlays may not align with older surveys.
| đź’ˇTip: Always confirm both datasets share the same CRS before comparing volumes or elevations. |
How to avoid CRS mismatch issues
Set your site CRS carefully when creating a new site.
Coordinate with your team before making any CRS changes.
Keep notes on which CRS each dataset was processed in.
Reupload and reprocess surveys or designs after any CRS change to maintain accuracy.
I still can't do it!
We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.
If you're stuck, you can connect with our support team by clicking the question mark button at the top right corner of your user portal.
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