OPUS Height Conversions


Hi ROCK Community,

I’d like to hear input on others utilizing the OPUS report for their Emlid Reach RS2. I understand the general process for pre processing the LiDAR and using the E LON/W LON & EL HGT with OPUS. My question is specifically around when you’ve reprojected a project into State Plane, and then need to convert the HEIGHT reading from OPUS into your state plane GCP.

Here are my questions:
When converting the project from WGS/Ellipsoid to state plane, can the ORTHO HGT be used safely to represent the Z value of the ground?
Can you simply convert the 79.543(m) to 260.96(ft) to get the height in feet? Or is there some other computation required?|
What does the 0.742(m) number represent in this ORTHO HGT example?

As a background, when I was recording my GPS, I did not input any antenna height into Reachview3 app. when I submitted to OPUS, I added the 2.0 meters to account for the height of the 2m pole. My goal here is to solidify the GPS alignment process when not using survey controls and relying on the OPUS solution from the RS2 Base readings.

You don’t confirm using other GCPs?

You are right… the ellipsoid and orthometric height are different. Where I am from the difference is 17m.

Blindly trusting your conversion from ellipsoid to state plane is very risky. You should really employ GCPs to verify your paranoia. When I convert, I am ALWAYS out and calibrate to my GCPs.

How else would you prove your data? Could be very expensive.

The question I’m wondering about is if ORTHO HGT is essentially the same level of accuracy as EL HGT, just on a separate vertical coordinate system (ellispoid vs navd88 geoid18). I know face value the numbers are completely different , but are they both accurate in their respective coordinate systems?

This question is more about the elevation accuracy of one specific point, being that of the Base station. I would think the accuracy of the Base station would reflect the accuracy of your GCPS, that is when using a BASE and ROVER system and not any outside source.

Ah yes, I understand now.

Yes, it is the same accuracy. In fact, depending on the job, I just leave my stuff in ellipsoidal.