I started a free trial with Point One Navigation so I could use their NTRIP service with the Reach RX. Setting it up was fine with no issues. For my area of South Texas, I set up the Reach RX to NAD83 South Central Texas and NAVD Geoid 2018 for the vertical. After I shot my points, I came back and noticed ALL my Z coordinates were off by negative 3 feet on average.
I contacted Point One Navigation and they told me they use ITRF 2014 and would need to convert. I’ve used Smart Net in the past for NTRIP and had no issues with the Z elevation. What would be the correct way to convert? From the forum I have used HTDP computations and that appears to work. Is that the best way?
To make matters more complicated, the existing benchmarks on site are in a custom coordinate system.
You need to consider wether or not the passive “benchmarks” are truly benchmarks. Have you checked the NGS data sheets for the info of the benchmarks ? Just because there is an elevation accompanying the horizontal coordinates doesn’t mean they are valid. Are the benchmarks in the same datum ?
What’s the accuracy class of the benchmarks ?
NAD27 coordinates will not work with NAD83 , either horizontal or vertical. Also, using an RTN service, vertical accuracies in the elevation component are not as accurate as elevations determined by precise leveling techniques.
First, I’d like to second @Africawaterdoc’s words. Localization can help you work with the corrections in ITRF2014. To do this, you’ll need some points with known local coordinates. Another option is setting up your project in a custom coordinate system. In this case, you’ll need to specify the transformation parameters from ITRF2014 to NAD83 when creating a custom CS.
As for the points that are already collected, you can convert their coordinates. Here is how to do this:
You’ll need to convert geographic coordinates from your CSV file (they are in ITRF2014, the same as your base) to NAD83 using online converters.
Ensure your CSV file with the coordinates after the conversion has Latitude, Longitude, and Ellipsoidal height columns.
Create an Emlid Flow/Emlid Flow 360 project with the NAD83 / South Central Texas coordinate system and NAVD88 vertical datum.
Import your CSV into it, the app will calculate projected coordinates and orthometric heights automatically.
Point One is really trying to get “drone mappers” to use their service. They have priced it very low compared to other RTN providers. The one thing they fail to mention is what you found out, they use ITRF. Most “drone mappers” in the United States will have clients needing their data in NAD83 (Choose your flavor) and NAVD88 (Choose your Geoid).
A workaround so that you do not have to keep transforming to NAD83 is to have 2 Emlid units. Make your own known point by using Point One, then use NGS HTDP tool to transform the point into NAD83. Then setup a base emlid on your new NAD83 point and use Emlid’s caster to broadcast corrections over NTRIP to your drone and/or your rover for collection of control points for GCP and Check Point use.
Also keep in mind that unless Point One’s network changed it was touted as a decimeter solution with getting down to low centimeter accuracy/precision in some cases.
