Content_Under_Construction_(<-- click this link to access pages/files described below)
- State plane coordinate system elevation factor computation and comments.
- HTML file exported from Matlab used to compute a "three-point fix" or resection using known coordinates of observed points and angular measurement.
- Computing a receiver position from RINEX file pseudoranges and SV coordinates from a precise orbit file. (not complete)
- HTML file exported from Matlab showing level adjustment computations using least squares. (not complete)
- Matrix inversion explained.
- Method of least squares explained with simple example. (updated 29 Sep 2019 - still in work)
- Calibration Base Line check computations.
- Rotation matrices explained.
- Computation of geopotential numbers and dynamic heights. Addresses an erroneous approach posted to a website.
- Computation of normal gravity at a specified latitude using WGS84 polar and equatorial values and the closed formula of Somigliani.
- 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.
- Alternate equations for computing e^2 are equivalent.
- How to compute the GPS week and day of week for a user specified date. - (UPDATED 23 Oct 2019)
- How to compute the unknowns in a three-point fix (last update 16June 2019)
- LU decomposition explained.
- Leveling adjustment elaborately explained.
- Are interstation distances determinant of baseline accuracy? (latest update 4 May 2020) Not nearly complete.
- 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
- 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
- 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
- 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
- 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
- Comparison of xGeoid20B height differences and the differences from differential leveling. Validating xGeoid20 as tool to move from NAVD88 to NAPGD2022
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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