When using a DB_REF coordinate system, you might see your survey data looks shifted against the background map. Don't worry—your data is completely accurate. This article explains that this is only a visual offset caused by prioritizing the precision of your survey coordinates over visual alignment with the map. We'll cover why this happens and what you can do about it, such as using a local site calibration.
You may notice that after processing a survey using the DB_REF coordinate system, your site data doesn't seem to align perfectly with the background map imagery. This article explains why this visual shift occurs and what it means for your data.
First, and most importantly: Your survey data is correct, and its coordinates are accurate. The shift you are seeing is purely visual and does not affect the precision of your measurements.
What is the issue?
When you view your processed survey on a site using the DB_REF datum, you may see a noticeable offset between your survey data and the background map tiles (like satellite imagery). This can also happen with other map data you import, such as KML files.
Again, this is only a visual discrepancy. The measurements and coordinates of your survey data are accurate and can be reliably used with your design files.
Why does this happen?
To understand the shift, it helps to think of coordinate systems as different languages. For everyone to work together on the Propeller Platform, we translate all data into one common "language" or universal map system (called WGS84).
- For most coordinate systems: Many systems, like GDA94/2020 in Australia or NAD83 in the US, are very similar to our universal system. The translation is straightforward, and everything lines up perfectly.
- For the DB_REF system: The DB_REF datum is fundamentally different from the universal system we use for background maps. It's like translating between two very different languages.
To ensure your data is accurate and usable with your other design files, we apply the correct parameters to your survey. This correctly "translates" your coordinates. However, when we apply these same parameters to the background map, it causes the visual shift you see.
This leads to a trade-off:
- If we prioritize correct coordinates (which we do): Your data is accurate and aligns perfectly with your designs, but it will appear shifted against the background map.
- If we prioritized aligning with the background map: The map would look aligned, but your survey coordinates would be incorrect and unusable for professional work.
We believe that ensuring your survey data has correct, usable coordinates is the most important priority.
What can you do?
If the visual offset is a concern for your workflow, you have a couple of options:
- Use a Local Site Calibration: The best solution is to use a local calibration file for your site. This will align your survey data and the background map correctly, eliminating the visual offset.
Turn Off the Background Map: If the offset is distracting, you can simply turn off the background map imagery in the platform. Your survey data will still align perfectly with all your design files.
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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