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Page history last edited by donngs@... 2 years, 8 months ago Saved with comment

Content_Under_Construction_(<-- click this link to access pages/files described below) 

 

  1. State plane coordinate system elevation factor computation and comments.
  2. HTML file exported from Matlab used to compute a "three-point fix" or resection using known coordinates of observed points and angular measurement.
  3. Computing a receiver position from RINEX file pseudoranges and SV coordinates from a precise orbit file. (not complete)
  4. HTML file exported from Matlab showing level adjustment computations using least squares. (not complete)
  5. Matrix inversion explained.
  6. Method of least squares explained with simple example. (updated 29 Sep 2019 - still in work)
  7. Calibration Base Line check computations.
  8. Rotation matrices explained.
  9. Computation of geopotential numbers and dynamic heights. Addresses an erroneous approach posted to a website.
  10. Computation of normal gravity at a specified latitude using WGS84 polar and equatorial values and the closed formula of Somigliani. 
  11. Discussion of an issue raised by a post to the Beerleg site. Some discussion of plotting GEOID12B modeled data  For these pages see: Bill93_project and Plotting a grid of points at one-minute interval . The input file for GEOID12B and the output from the program are linked on the "Plotting..." page.
  12. Alternate equations for computing e^2 are equivalent.  
  13. How to compute the GPS week and day of week for a user specified date.  - (UPDATED 23 Oct 2019)
  14. How to compute the unknowns in a three-point fix (last update 16June 2019)
  15. LU decomposition explained. 
  16. Leveling adjustment elaborately explained. 
  17. Are interstation distances determinant of baseline accuracy?  (latest update 4 May 2020) Not nearly complete.
  18. Using Newton’s method to compute the square root of a value. Using Newton’s method to solve for the square root of an unknown number using Matlab
  19. Computing e^2 (eccentricity squared of GRS80 ellipsoid from defining constants: a, J2, GM and omega, using Matlab. Computing first eccentricity squared of GRS80 using defining constants
  20. Computing geodetic coordinates (lat, lon, ht) from geocentric coordinates (X,Y,Z) in GRS80. Used formulas in a paper by Gerdan and Deakin. Coded using wxMaxima 5.44.0.DeakinXYZtoLLh.html  
  21. Exploring the computation of an orthometric height (H) from ITRF2014 (epoch 2010) ellipsoid height (h). Shows numeric results using four Internet-based tools. Tools are from National Geodetic Survey (US), Natural Resources Canada, UNAVCO and the National Geospatial-Intelligence Agency. Preliminary PDF is here: WGS84_h2H.pdf   
  22. Some discussion and exploration of the differential leveling portion of the US NGS Geoid Slope Validation Survey of 2017. Geodetic_Leveling_GSVS2017 . Note that there is a free to view/download version of the paper Derekvan Westrum, D., Ahlgren, K., Hirt, C. et al. A Geoid Slope Validation Survey (2017) in the rugged terrain of Colorado, USA. J Geod95, 9 (2021). https://doi.org/10.1007/s00190-020-01463-8 available here:  https://link.springer.com/article/10.1007/s00190-020-01463-8 
  23. Comparison of xGeoid20B height differences and the differences from differential leveling. Validating xGeoid20 as tool to move from NAVD88 to NAPGD2022  

 

Using superseded information on NGS data sheets   

 

Prompted again by discussions on web sites, I developed a page exploring information appearing on the data sheet for PID:AH1762. This is a tidal BM/high accuracy horizontal control point/differentially leveled BM. It has participated in a number of projects leading to changes in the source for its currently published NAVD88 height. This data sheet is of interest as it shows that sometimes good/better data can be superseded.  

 

I also discuss OPUS-DB solutions for this point. A number of observation sessions have observed subsequent to those used to compute published values. Can these solutions be used to determine whether the point is undergoing change?

 

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