Ellipsoids, Datums, Realizations, Grid to Ground, and Site Calibrations Explained
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- Опубликовано: 8 дек 2019
- Ellipsoids, Datums, Realizations, Grid to Ground, and Site Calibrations Explained. I created this video to help clarify some of the more difficult topics relating to Land Surveying with GPS equipment. It is a long video, but I cover a lot of information and provide drawn out pictures with explanations.
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Ya did good, kid. Doing God's work here. Respect for knowing what's important, and sharing it. Parameters, units, definitions, proper nomenclature.
Surveyor in Arizona here, I completely agree with what you said about site calibration. I have used this method for years without issue.
Great video Anthony.
I appreciate you making this video
Not bad. However, I disagree with two points. The reference (ellipsoid) is the mathematical model that we use for computations. It has a semi-major axis, a semi-minor axis and the flattening as well. It is akin to the geoid which is the approximation to mean sea level over the entire earth. However, we cannot use the geoid to perform computations because its shape is too irregular; thus, surveyors have introduced the reference ellipsoid to make computations. Due to this, a phenomenon called 'the deflection of the vertical' occurs because computations are done on one surface and measurements are taken from another. This error has to be corrected also. Moreover, for the geometric (horizontal) datum NAD27, the reference ellipsoid is Clarke 1866 not 1863. Apart from that, it was quite interesting. Indeed, surveying is a fascinating field.
Thanks
Great great.
We may know, but we can learn more details.
Make more content. You’re the only one.
Still a little fuzzy on your explanation of the Lat/Long Scale Origin. Would I get that point of scale origin from the 'Projection Parameters' in my GNSS survey report? Under that column (for PAN) it will give me a Standard Parallel 1, Standard Parallel2, Central Meridian, Latitude of Origin , False Easting, False Northing. Would I therefore publish the 'Central Meridian and Latitude of Origin' for that Scale reference.? Excellent presentation! Looking forward to others.
Thanks for the video. I realize that I am 4 years late to the party, but I have a question that I hope you can answer. Are scale factors always less than one? We are currently bidding a job, a 4 mile (approx.) extension to the sewage outfall in the bay at Bayou La Batre, Alabama, and when I look at info on the NGS websites (assuming that I am accurately interpreting said info), I see scale factors slightly over one (e.g., 1.00000213). Does this seem correct to you. I have not worried too much about this in the past because our jobsites have been so small, but on this one, the difference between grid coordinates and ground coordinates could be significant. Thanks for your help.
OK, so, you're ending your calibration after two shots for horizontal and one for vertical? Or you're intentionally shooting the two points that he's split the project in half at the longest distance apart, and then shooting the other points and including them horizontally in your calibration?
I use Trimble site works, not sure if you can do just two horizontal and one vertical.
26:44 What do you mean at this point? For example, that we shoudn`t have ay projections systems assigned to project in our field controller when using calibration. If we do have some UTM projection assosciated to a project instead working with geodetic coordinates (latitudes and longitudes only) we would get wrong site calibration? Can you explain a little better about this subject please?
When you use site calibration you are creating a local projection. If you are using a defined projection like UTM and you set up on a known point and the design was done in UTM and all your options are set the same as the design surveyor then you shouldn't need a calibration. It's too many variables. Use site calibration or a defined calibration but I also do not recommend mixing them.
Could you please explain what is 20906000 and what is the unit of that amount...
Best regards
20,906,000 is in feet and is the mean radius of the Earth used by the U.S. Coast & Geodetic Survey (USC&GS), now the National Geodetic Survey (NGS) to compute the ellipsoid reduction factor for distances when using State Plane or UTM coordinates. -- Reference page 49, NOAA Manual NOS NGS 5 "State Plane Coordinate System of 1983" -- www.ngs.noaa.gov/library/pdfs/NOAA_Manual_NOS_NGS_0005.pdf
That’s true,
The ellipsoid and geoid are hypothetical. You are a fool if think they are facts.