Please answer for me another question....
If you think your geoid model is so accurate then why the need to do actual topography survey?
why not just get your x,y,z from the geoid model itself????
hahahahahhah
All this is explained in elementary surveying books. A text on geodesy would be too difficult to follow as an introduction.
I guess none of you have ever bothered to read up on it based on the comments made in this thread....hahahhahahhahaha
FrancisH, post: 420533, member: 10211 wrote: If you think your geoid model is so accurate then why the need to do actual topography survey? why not just get your x,y,z from the geoid model itself????
This question shows that you don't know what a geoid model is and haven't read up on it, or else you are just making up misleading questions to antagonize readers. A geoid model has almost nothing to do with the surface features. Look at the diagram earlier in the thread. A geoid is one way to model gravity's variation over a geographic area, not the surface.
David Livingstone, post: 420520, member: 431 wrote: NGS updates the Geoid daily
Please explain. I thought the most recent official update was Geoid12B several years ago, with a preliminary later one available for examination but not adopted.
Bill93, post: 420544, member: 87 wrote: Please explain.
I believe that statement was made with tongue in cheek, in solidarity with the ignorant statements made by one particular participant in the discussion.
I believe that statement was made with tongue in cheek, in solidarity with the ignorant statements made by one particular participant in the discussion.
jahahahhahahah you call my statements stupid and yet someone who says geoids are updated daily is considered tongue in cheek???? hahahahhahahahahahahahahahahahahhahaha
This question shows that you don't know what a geoid model is and haven't read up on it, or else you are just making up misleading questions to antagonize readers. A geoid model has almost nothing to do with the surface features. Look at the diagram earlier in the thread. A geoid is one way to model gravity's variation over a geographic area, not the surface.
oh boy oh boy, the gravity based geoid is modeled near values of MSL for elevations. In short elevations/heights when referred from the geoid model would give you MSL height values. If you wanted to get heights relative to MSL then you use a geoid value for your BASE. The heights that you get from your ROVER is RELATIVE TO YOUR BASE HEIGHT. If you changed your BASE HEIGHT, your ROVER HEGHT will changed proportionally.
This being the case, if you know the ABSOLUTE MSL/MLLW HEIGHT of your BASE then it DOES NOT MATTER if you use ORTHO HEIGHTS or ELLIPSOIDAL HEIGHTS since what ever elevation is fed into your base, your rover elevation will be based on this.
jeeeeezzzzzzz, a lot of experts here that do not even understand the receivers are DUMB BOXES that will accept whatever elevation you feed into it.
Yeah, and then all of your orthometric heights have the geoid separation applied to them twice and are incorrect. I have seen this happen and it is a mess. You are essentially inflating the ellipsoid to the geoid height at the base.
Yeah, and then all of your orthometric heights have the geoid separation applied to them twice and are incorrect. I have seen this happen and it is a mess. You are essentially inflating the ellipsoid to the geoid height at the base.
huh?have you ever post processed GPS data? What software? Can you tell me how you can double your geoid separation value?
Please don't talk nonsense if you have never processed gps data before.
hahahhahahahah
FrancisH, post: 420550, member: 10211 wrote: This being the case, if you know the ABSOLUTE MSL/MLLW HEIGHT of your BASE then it DOES NOT MATTER if you use ORTHO HEIGHTS or ELLIPSOIDAL HEIGHTS since what ever elevation is fed into your base, your rover elevation will be based on this.
The difference between ortho and ellipsoidal at one location will not be the same as the difference between ortho and ellpsoidal at another location. This is because ortho takes into account the varying gravity and ellipsoidal does not.
Yes, if you are B feet ellipsoidal at the base and R feet above the base at the rover according to GNSS, you are B+R feet ellipsoidal at the rover.
But if you are X feet orthometric at the base, and R feet above your base at the rover according to GNSS, you are NOT in general X+R feet ortho at the rover. If you (or your tools) do not also correctly apply a geoid model, and you are far enough away that the gravity is different at the rover, water may not run the way you expected.
If you are working in a small area, you may get away with ignoring gravity variations, but you should understand what you are ignoring.
I'm done with this discussion.
FrancisH, post: 420556, member: 10211 wrote: huh?have you ever post processed GPS data? What software? Can you tell me how you can double your geoid separation value?
Please don't talk nonsense if you have never processed gps data before.hahahhahahahah
I rest my case. Same understanding of geodesy as US boundary surveying. You should stop, you are embarrassing yourself.
But if you are X feet orthometric at the base, and R feet above your base at the rover according to GNSS, you are NOT in general X+R feet ortho at the rover. If you (or your tools) do not also correctly apply a geoid model, and you are far enough away that the gravity is different at the rover, water may not run the way you expected.
haahahahahahahahahhaha so, let me know please GPS guru....how FAR AWAY will rover have to be from base to inroduce a "significant" error??? Please give me a number and not "If area is small" or "area has siginificant variations in geoids" BS.
I rest my case. Same understanding of geodesy as US boundary surveying. You should stop, you are embarrassing yourself.
instead of answering in vague manner why can't YOU NAME YOUR SOFTWARE & HOW YOU USED IT????
The difference between ortho and ellipsoidal at one location will not be the same as the difference between ortho and ellpsoidal at another location. This is because ortho takes into account the varying gravity and ellipsoidal does not.
Quick someone call the IHO and tell them that their standard use of GPS receivers for bathymetry work is ERRONEOUS ALL THESE YEARS!!!!
Quick it means all bathymetry maps in the world is ERRORNEOS!!!
FrancisH, post: 420550, member: 10211 wrote: oh boy oh boy, the gravity based geoid is modeled near values of MSL for elevations. In short elevations/heights when referred from the geoid model would give you MSL height values. If you wanted to get heights relative to MSL then you use a geoid value for your BASE. The heights that you get from your ROVER is RELATIVE TO YOUR BASE HEIGHT. If you changed your BASE HEIGHT, your ROVER HEGHT will changed proportionally.
This being the case, if you know the ABSOLUTE MSL/MLLW HEIGHT of your BASE then it DOES NOT MATTER if you use ORTHO HEIGHTS or ELLIPSOIDAL HEIGHTS since what ever elevation is fed into your base, your rover elevation will be based on this.
jeeeeezzzzzzz, a lot of experts here that do not even understand the receivers are DUMB BOXES that will accept whatever elevation you feed into it.
If your dumb box is set up to use a geoid, the separation will reflect the undulations of gravity. Your ellipsoid and ortho heights may be 56.00 feet different in one place and 56.055 in another. I train and support numerous offices on these concepts. There are folks here that make me look like a newbie. You would do well to stop showing both arrogance and ignorance and listen a little bit. There is nothing wrong with not knowing everything. The problem arises when you refuse to admit that you dont. All you are accomplishing is alienating the most qualified group around and sucking up bandwidth.
FrancisH, post: 420532, member: 10211 wrote:
please read up on the basics of GNSS surveying. hahahahahhaha very funny thread...brings out the dimwits who think that the orthoheight from their ROVERS is based on a geoid model. hahahahhahahahah
Where have you been Francis? Leica's RTK gear has allowed the user to load a geoid model in the rover for many, many years. If the user wants to save ortho heights, the rover extracts the geoid separation at its position (not the base position), does the math, and stores the ortho height. Easy, Peasy.
And please read (for the first time) base9geodesy's post at the top of page 7 (Post #121) regarding WGS84. You would cure a lot some of your ignorance if you take a minute to read his post. The poster is the retired Chief Geodesist of the NGS, Dave Doyle.
FrancisH, post: 420567, member: 10211 wrote:
instead of answering in vague manner why can't YOU NAME YOUR SOFTWARE & HOW YOU USED IT????
It's not about software child, it's about math.
Sorry, I meant to say "It's not about the software child, IT'S ABOUT THE MATH"
Where have you been Francis? Leica's RTK gear has allowed the user to load a geoid model in the rover for many, many years. If the user wants to save ortho heights, the rover extracts the geoid separation at its position (not the base position), does the math, and stores the ortho height. Easy, Peasy.
yes, that's what I have been saying all along, you replace your vertical datum from WGS84 to EGM96 or EGM2008 ALL your RTK point elevation will SHIFT by a CONSTANT VALUE. I think you have not even tried this or you would not even be here arguing with me.
And please read (for the first time) base9geodesy's post at the top of page 7 (Post #121) regarding WGS84. You would cure a lot some of your ignorance if you take a minute to read his post. The poster is the retired Chief Geodesist of the NGS, Dave Doyle.
How can you be a Chief Geodesist and not even know that most countries have BMs established throughout the nation derived from tidal observations?
Let me see, why would I rely on an ortho value made from referencing a geoid model when I could occupy a BM with known MSL/MLLW value and transfer that to my rover points using ellipsoidal heights?
Wouldn't my rover points also be carrying MSL/MLLW values if base is referred from MSL/MLLW value?
hahahahahhaha
