Another boat with a Ping sonar. From the dataflash, can you output depth and rtk corrected gnss coordinates? I usually just use the dataflash to see why my copter is flying funny or geotag images lol! I know Ping uses their own com protocol so I didn’t know if it would work. Basically want to bring in the points to Global mapper, adjust for the elevation of the gnss antenna to the sonar and create a surface.
The DPTH messages holds the rangefinder distance and the lat,lon,alt of the vehicle. Maybe this is what you need? The lat, lon, alt will be from the EKF but this should be at least as accurate as the GPS being used.