Navigating Heights - The Role of Geoid Models in Modern Surveying

[@lilanedaria]

Your videos and teaching methods are fantastic and I have learned so much thanks to you!

[@lztoniolo]

Your videos and explanations are much better, more detailed and clear than all my professors together lol (Brazil follower here). Outstanding content you have in your channel and I always waiting for your content. A big service for future generations and people of interest! Thanks great man. 🙏👏👏👏

[@ThatGratefulGuy]

Great video! Thanks. I enjoyed the concise format, clear examples, and strong closing/final thoughts.

[@TechWizeGuy]

As always awesome content, awesome format and awesome explanations! Nobody gets into the weeds and pulls them up at the roots like you!

[@aidanburfield2670]

Thank you for sharing!! You always do a great job with explaining and really breaking down the content and you do it in a manner that's easily understood! You always pick great topics that aren't of talked about, but are very important in this industry! Thanks again for sharing!!

[@lofininja5917]

always something to learn. Thanks

[@gunningopher]

Great description. This subject can be quite confusing and you do a really good job of breaking it down. Your channel stands above most other survey ones on KZbin. When Geoid 03 came out I mapped the difference between it and '99 and was really shocked at how much it had changed. If you haven't done that, I recommend giving it a try. I kept it to my local area (So Cal) but you can do it at whatever area and resolution you'd like. What you do is create an 'elevation' grid using N as the 'elevation' on both geoid models (there are a few ways to do this). That alone creates an interesting contour or shaded surface of that geoid model for the area you cover. The real interesting part is if you do a delta surface between 2 geoid models and contour or color that. It basically shows what you described in your comparison between N over 1km vs 10km, but for a wider area. I did all this because we had 2 crews working on a topo project. One of them started the base and the other just connected to its correction message and started working. The base was set on a known control point. One of the crews couldn't figure out why the were seeing a different elevation at the base and couldn't get a good check. I got called and after a while I realized what they had done. One crew was using 99 and the other was using 03 in their project setup. When the base was started from a data collector using G03, it dutifully computed h and was sending that ellipsoid height to the rover over the RTK radio. Then when the rover received that ellipsoid height, it dutifully computes that h into an ortho height using the geoid model it has. What you say is absolutely true; our software can make a very complex system seem simple and we have far too many button pushers out there. We now have contractors doing this geodetic surveying and I've heard some frightening stories. Half of these guys got their training from a guy they know who was shown how to use this by a sales person. I'm working to fix that in California. We have Professional Registration and protected practice laws for a reason. The public needs to be able to trust that the people they are paying to do work are reasonably competent. As far as I know, no version of RTCM or CMR has ever included the geoid model in its correction, so the rover has no way of knowing what went into producing the height of the reference. I created the delta N surface I described to see for myself and share just how dynamic geoid models can be. I thought about doing the same thing when subsequent models came out, but never got around to it. In my area, we've had a really good gravity model since '03 came out. We're lucky in Coastal California, because we have a lot of economic activity, which lends itself to having a lot of Land Surveying, which in turn means that we end up with a lot of data in NGS models.

[@ahillstosky]

I appreciate the video; great content as always 😁

[@flyingsurveyor]

Great video as always

[@freedomhillbilly348]

Seems to me the quest for standardization has created more confusion and can introduce more error than is worth the cost. I may have missed it, but can after-the-fact corrections be made for the misstep of failing to specify a GEOID model when doing the fieldwork? I'm new to this GNSS stuff and I've tinkered for over two years with my equipment and technique to where I have finally achieved 6" accuracy. Hoping closer study of this reference frame and modelling stuff will get me closer to tenths accuracy. Thanks for your videos!

[@The3rdDimensionSurveying]

Well luckily for us the NGS is working on a new vertical datum that should make life for surveyors much easier. There will be a video on that as we get closer. Absolutely you can for data collection, not for staking however. I post process all my raw data in Starnet, I very rarely use any data directly out of the DC. Starnet applies its own geoid model directly to the raw data so it would make no difference. If there are stakes in the ground, which was the example in this video, it usually means a trip back out to the field. Thanks for the comment!

[@ls2005019227]

This is a super dry (like watching paint dry).....but an absolutely necessary to understand subject (for all of using GPS). The effort by the NGS to correlate conventionally leveled orthometric heights, with ellipsoidal heights [for the purpose of developing better geoid models], was known as "Height Modernization." This is probably over-simplifying it, but I like to think of building a geoid model as bending a ruler.....for the sole purpose of correlating an ellipsoidal and a geoid height to produce a result that agrees with previously determined orthometric heights. You did a fantastic job explaining a somewhat difficult subject!

[@AlphaG5583]

Also ignoring elevations with a gps can introduce horizontal errors. This is more to do with scale factors, but having -999ft in elevation as a set of points to layout in gps is going to be feet off if your site is say at sea level when you check the distance with a total station. So getting elevations correctly is important for gps not just in verticals but horizontals also.

[@The3rdDimensionSurveying]

@@AlphaG5583 Absolutely, great point. The elevation factor! I’m actually working on a grid to ground video now that will bring that up.

[@AlphaG5583]

Awesome, you're a beaut bud