Hi Matt,

We have faced with some unclear shifts of waypoints during export-import procedure through “Lowrance USR” file format.
Later we tried to replicate this issue from scratch and it was still there, here are the details:





We exported this set with one waypoint into “Lowrance USR” format then imported back into the same project:
All offsets seemed to be set to zero during the import:



As a result we've got 2 waypoints on the map:



With some distance between them:



Our first thought was that this is how RM displays same waypoint, so we tried to export “both” waypoints into CSV format.
Surprisingly both waypoints were there and had slightly different coordinates:



Obviously 20-30cm is not too much, still wondering why we’ve got the difference, could you please check this?

Thank you!

This is because Lowrance uses an integer Mercator metre format to store positions, so when you write to the USR format you will (almost) always lose a little bit of precision. You could potentially lose up to around half a metre of precision in a round trip to the USR format, so I would not recommend it unless you need it to put waypoints on your unit.

Oh, I see.
It looks like rest of supported export-import formats will loose our waypoint symbols – is this correct?

If you want to keep waypoint symbols during a round trip to a Lowrance device then you will need to use USR, yes. I'm afraid you will just have to tolerate the slight loss of accuracy - you won't get a higher level of accuracy on the unit anyway. For exporting to anything else, better to choose another format such as CSV or GPX.

Two clarifications.
When we export waypoints in gpx format from 7Ti to RM2 we can see the waypoints symbols in RM2. But if export going from RM2 to 7Ti any symbols looks like a blue points. Matt, can you explain why this happen? Thanks!
And two - it is no difference between gpx and usr format in this case. Any format will be changed by 7Ti after import and you we will have lose a bit of precision. You can try export gpx from RM2 to lowrance and after export these points in gpx to RM2. I have about 0.7 m between the same points.
And yes 7Ti have a bug with new software upgrade - you cannot read any exported USR(2,3,5) format from Ti. At least RM2 and Global Mapper cannot read this format after last upgrade 7Ti. And if you try to load exported usr file from Ti to Ti you will see the message "Error parsing waypoint".