# OPUS ORTHO Height Conversions

Hi Emlid Community,

I’d like to hear input on others utilizing the OPUS report for their Emlid Reach RS2. out in the field, I am using the logging capability with the RS2 and Reachview3 app to record GPS for 2+ hours. then converting the file using RTKCONV and submitting to OPUS. When I was logging, 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.

Here are my questions:
Does the ORTHO HGT 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?

Hi Russ,

The orthometric height is the ground Z height for GNSS units. It is ideally equal to the ground height above mean sea level that would be obtained using a traditional optical leveling run and it would be exactly equal if a perfect geoid existed for the survey area. But in reality, a perfect geoid doesn’t exist and they update them when better data becomes available.

For the purpose of GNSS surveys, you can reference your Base’s orthometric height as ground Z height and specify the geoid that was used in its calculation. In this case it’s NAVD88 computed with Geoid18. This would be repeatable by another surveyor with a GNSS who sets up their base in the same location. And if an improved geoid is released in the future, then your height could be easily converted.

Yes you can convert meters to feet from the opus report. Use either US survey feet or international feet for conversion depending on which is used in your area.

The 0.742m is the estimated error of the opus solution in the Z direction. I forget if it is RMS or 1 standard deviation, you’d have to look it up. Your project requirements should define what an acceptable error is here. Generally longer observation times will reduce the error.

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Hi Russ,

@Africawaterdoc is absolutely right!

It’s overall RMS.

A small note: we have the OPUS logging preset in ReachView 3. This way, you don’t need to convert anything afterward.

If you want to have the log with all constellations, there is still no need to use RTKCONV. It can be easily done in Emlid Studio with these conversion settings:

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