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Read the following descriptions. View those of interest by clicking on their links. No warranty, expressed or implied, is offered with these papers. Use at your own risk. You may save the papers to your own computer.

Keeping score on flickr (2023), the QPS score of any photo stream on flickr allows one to simply assess the quality, popularity and strategy (QPS) of any photographer independently of their length of usage. View the derivation and usage here.
View "Keeping score.pdf"

ECEF & EGM the Software, called "ECEF & EGM in WGS84" (2022), is an open-source, free-to-use-and-modify, compiled Python application that converts lat/lon/hgt to and from ECEF, computes geoidal and orthometric heights, and north and south gradient (related to deviation of the vertical). The application also plots a geoidal contour of the world plus an interactive ellipsoidal globe in 3D that can be rotated and zoomed. The User's Manual that gives more information and the URL of the FTP site, userID and password where the software can be downloaded is here.
Download "ECEF & EGM in WGS84"

"Subsea SLAM EKF Simulation (2018)" Simultaneous Mapping and Location (SLAM) is an observational and mathematical technique that enables walking, rolling, sailing or swimming robots to navigate indoors (or in a park with trees, or anywhere for that matter ... just not in a desert or a seafloor with no topography) without any external (absolute) positioning aid such as GPS, USBL or LBL.
Download "Subsea SLAM EKF Simulation"

"Kalman Filter for Arduino IMU-GPS ArduPilot (2018)" An ArduPilot APM 2.5 is the heart of a hobby drone's navigation system. The ArduPilot's onboard sensors alone are totally adequate to control a UAV in real time. Nevertheless, having a 25Hz IMU relative sensor and a 5Hz GPS absolute sensor in the same "box" provides an opportunity to improve them both in post processing with a Kalman filter (Kf) ... despite the hobby quality of the sensors themselves. This paper describes the 15-state Kf developed for this purpose.
Download "ArduPilot Kalman filter"

"Characterizing an IMU for a Raspberry Pi (2018)" The Raspberry Pi stands out among single board computers due to its thriving market in daughter boards called HATs. The HAT in this study is the BerryGPS+IMUv2 from Australia. The IMU (inertial measurement unit) in this HAT is the (inadequately-specified) STMicroelectronics iNEMO LSM9DS1. This study analyzes 12 hours of raw data from this IMU, computes the Allan deviation plots for the gyros and accelerometers, reads the in-run bias stability and the angular and velocity random walk specifications from those plots, and compares these specifications with other MEMS IMUs in the marketplace.
Download "IMU for Raspberry Pi"

"Multi-language, multi-platform numerical test in Linux OS (2016)" Now updated for the Raspberry Pi 3, quad core ARM Cortex-A53. A numerical test program is written in Matlab, C, FORTRAN, Go, Julia, Ruby, Python, R, SciLab and Octave and executed on an Intel i3 laptop, an Intel Atom netbook, and Udoo, Beaglebone Black and Raspberry Pi 1B & 3B ARM single-board computers ... all running various distros of Linux. Execution times are compared.
Download "Numerical test"

"Reintroducing (refracted) first breaks with notes" The paper below "Reintroducing (refracted) first breaks into ocean-bottom seismic positioning" (2015) was delivered at the 2015 SEG conference in New Orleans. Wide-azimuth, far-offset, first breaks deliver USBL-quality positions and enable the quantification of angular source-array effect and node oscillator drift.
Download "Reintroducing (refracted) first breaks with notes.pdf"

"Hydrometronics First Break Analysis," called HmFBA (2015), is a positioning application that loads, conditions, picks (four different techniques), saves and adjusts (sequential and simultaneous least squares) wide-azimuth, far-offset SEG-Y or Seismic Unix (SU) Ocean Bottom Seismometer (OBS/OBC/OBN) gathers for best position (coordinates). It solves for a vertical velocity gradient, optionally balances geometry in azimuth and distance, and provides QC statistics and plots. Download the whole user's manual or a two-page brochure.
Download "HmFBA User Manual.pdf"
Download "HmFBA Brochure.pdf"

"Test dataset for wellbore survey calculations" A short history of the Geodetic Corrections Subcommittee (circa 2007) of the SPE Wellbore Positioning Technical Section (formerly ... and still ... known as ISCWSA, Industry Steering Committee for Wellbore Survey Accuracy). The document "ReadMeFirst.pdf" contains a link to an FTP site with all the documentation for the test dataset.
Download "ReadMeFirst.pdf"

"Applying Real-Time Magnetic Declination in Arctic Marine Seismic" Curt Schneider, ION Geophysical, and Noel Zinn, Hydrometronics (OE Magazine, December 2013), Marine seismic surveying in the icy Arctic presents many challenges. Because of the lack of a tailbuoy, compass data must be corrected in real time for declination caused by the Earth's magnetic field, which, in the Arctic, varies constantly. On November 1, 2012, the ION Declinometer observed a geomagnetic event in the Beaufort Sea in which declination changed 12 degrees in 6 minutes at its peak. Magnetic observatories at Point Barrow and Deadhorse confirmed the event. This paper discusses the improvement of real-time declinations over modeled (gridded) declinations for seismic cable positioning in the Arctic.
View and download paper from ION Geophysical webiste
View and copy paper from OE Magazine website

International Patent WO 2012/161950 A2 (2012), Seismic Declinometer, "In seismic survey for icy waters, streamers are towed behind a vessel under the water's surface to avoid ice. GPS readings may not be consistently obtained because the ice prevents a tail buoy with a GPS receiver from trailing from streamer at the surface... The streamer's absolute position can then be used in conjunction with compass readings and can correlate various seismic sensor signals obtained along the streamer during the survey. The compass readings can be corrected for declination using declinometer readings, which can be compensated for iron effects from the vessel or other device carrying the declinometer."
Download "International Patent WO 2012/161950 A2"

"Cartographic Distortion Analysis: A Sampler" (2013) Cartographic distortion analysis is the process of computing and plotting distortion contours on a map containing an area of interest (AOI). It is also the process of optimizing projection parameters to minimize distortion in the (AOI). This paper provides a sampler for the Gulf of Mexico.
Download "Cartographic Distortion Analysis"

"A Kalman Filter for 3D Robotics ArduPilot" (2013) applies a loosely-coupled Kalman filter that integrates INS (inertial) and GPS to the 3D Robotics ArduPilot, a consumer-grade autopilot for "toy" drones that costs $316 including radio telemetry. The presentation graphically exhibits performance of the Kalman filter with ArduPilot walk-around data.
Download "A Kalman Filter for 3D Robotics ArduPilot"

"ArduPilot Mounted on Car and RC Boat" (2013) is the follow-on report to "A Kalman Filter for 3D Robotics ArduPilot". Here we assess the performance of the Kalman filter under different dynamic conditions than walking, viz. driving slowly and even more slowly towed by a remote-controlled boat on a neighborhood lake.
Download "ArduPilot Mounted on Car and RC Boat"

US Patent 8,332,174 B1 (2012), "Computer instructions for positioning a wire using sensor information". Computer instructions for determining coordinates for nodes on a wire secured to tow lines of a floating vessel for analyzing geological formations is provided. The computer instructions can use sensors in communication with a processor to determine the coordinates of nodes and provide azimuths tangential to the wire. A library of nominal values for polynomial coefficients, a library of known distances along the wire, and a library of preset limits can be stored in a data storage. The computer instructions can: receive sensor information, compute bearing, reorient the coordinates, rotate the azimuth, construct a polynomial algorithm, compute the azimuth, form a residual, compute updated differences until the residual is within preset limits, calculate local coordinates for nodes, and rotate the local coordinates from the local coordinate system to the projected coordinate system."
Download "US Patent 8,332,174"

"Earth Centered Earth Fixed: Scalable Visualization without Distortion" (2011) further evolution of the ECEF paper, this time presented to SWIGGIS (Supporting Women in Geography and GIS) at PBX Systems. Available in two formats. Unfortunately, the animations don't work in these PDFs.
Download "Earth Centered Earth Fixed" - Full Screen
Download "Earth Centered Earth Fixed" - Speaker's Notes

"What's Up? Tidal and Vertical Datums" (2011, revised 2013) reviews the celestial mechanics of tides, the relationship between mean sea level and terrestrial vertical datum types based upon geopotential numbers and why this is important for 3D visualization of the world. Presented at The Hydrographic Society Houston Chapter July 2011. Available for download full screen or with speaker's notes.
Download "What's Up?"
Download "What's Up? with speakers's notes"

"Ellipsoidal Orthographic Projection" (2011) describes the Ellipsoidal Orthographic Projection that is derived from Earth-Centered Earth-Fixed (ECEF) and Topocentric (East/North/Up) coordinates and suggests that the projection is a transition to undistorted 3D visualization of the Earth on a computer.
Download "Ellipsoidal Orthographic Projection"

"Earth Centered Earth Fixed: Powered by Blue Marble" (2010) is the latest revision of the ECEF paper showing computations using the Blue Marble Geographic Calculator. Presented at the Blue Marble User's Conference in Houston in October 2010.
Download "Earth Centered Earth Fixed: Blue Marble" with Speaker's Notes

"Web Mercator: Non-Conformal, Non-Mercator" (2010). Web Mercator is the mapping of ellipsoidal latitude/longitude into Easting/Northing using spherical Mercator equations. This is EPSG CRS code 3857 and EPSG coordinate operation method code 1024. The spherical and ellipsoidal forms of the Mercator projection are conformal. Web Mercator is not conformal. This paper provides equations for the varying scale factor in the Web Mercator, shows relative computation times with and without scale, and quantifies the distortions that make this projection a Non-Mercator. Presented at "GIS in the Rockies" September 2010.
Download "Web Mercator - Non-Conformal, Non-Mercator" - Full Screen
Download "Web Mercator - Non-Conformal, Non-Mercator" - Speaker's Notes

"Earth Centered Earth Fixed: A Geodetic Approach to Scalable Visualization without Distortion" (2010) updates the 2005 "Reservoirs to Regions" paper. Presented at the Houston chapter of The Hydrographic Society of America July 2010. Available in two formats. Unfortunately, the animations don't work in these PDFs.
Download "Earth Centered Earth Fixed" - Full Screen
Download "Earth Centered Earth Fixed" - Speaker's Notes

"Ellipsoidal Gnomonic Projection" (2010) provides an algorithm and Matlab code for a direct perspective ellipsoidal gnomonic projection via ECEF and topocentric coordinates, thus avoiding approximations such as the conformal sphere. The paper includes an image of the North American coastline projected in the ellipsoidal gnomonic.
Download "Ellipsoidal Gnomonic Projection"

"EPSG Wide-Zone TM Investigation and Recommendation r2" (2009) is a recommendation to the OGP (International Association of Oil and Gas Producers) to swap the EPSG Transverse Mercator method from the narrow-zone Snyder to the wide-zone Finnish algorithm. Lots of historical background on the TM projection.
Download "EPSG Wide-Zone TM r2"

"Orthogonality Preserved" (updated for vendor release in 2007) describes the fact that reprojection between conformal map projections preserves orthogonality, although straight lines in one projection may curve in the other. Connecting the ends of curved lines with straight lines artificially induces non-orthogonality in geophysical workstations. The paper describes quadrilateral tessellation as a method to overcome this problem. Technical reading without speaker's notes.
Download "Orthogonality Preserved"

"Accounting for Earth Curvature in Directional Drilling" (2005) is the PowerPoint presentation (with speaker's notes) accompanying paper SPE 96813 prepared for the Society of Petroleum Engineers Annual Technical Conference and delivered to the Industry Steering Committee for Wellbore Survey Accuracy (ISCWSA). The paper itself is copyrighted by the SPE and will have to downloaded from the SPE website.
Download "Accounting for Earth Curvature in Directional Drilling"

"Reservoirs To Regions: A Geodetic Approach to Scalable Visualization without Distortion" (2005) was delivered to the Americas Petroleum Survey Group. It describes Earth-Centered Earth-Fixed, topographic (local horizontal) and orthographic coordinates implemented in a 3D visualization environment. Lots of detail.
Download "Reservoirs To Regions"

"Molodensky-Badekas: Reducing the Consequences of Parametric Correlation in the 7-Parameter Shift" (2004) was delivered to the Americas Petroleum Group. It describes why the derivation of a 7-parameter datum shift for a small area of the Earth results in high correlations among the parameters, whose values are consequently determined by observational "noise". Use a 3-parameter shift or the Molodensky-Badekas 10-parameter shift instead. Technical reading with speaker's notes. A follow-up presentation (2005) analyzes Molodensky-Badekas reversibility, including the Dutch method.
Download "Molodensky-Badekas"
Download "Molodensky-Badekas Reversibility including Dutch"

"Using Cross-Correlated, Head-Wave and Diving-Wave Seismic Energy To Position Ocean Bottom Seismic Cables" (1999) is a term paper for Seismic Wave and Ray Theory (GEOL 7333) at University of Houston taught by Prof. Robert E. Sheriff. It includes Matlab code. A technical read.
Download "GEOL 7333 Term Paper"

"Ocean-Bottom Cable Detector Positioning: Acoustics versus First Breaks" (1998). This paper compares and contrasts two OBC positioning methods: independent acoustics and seismic first breaks. It explains that sub-meter results are possible with both systems. Two appendices offer a description of the SDCOORD first-break algorithm and a glossary of terms.
Download "Acoustics versus First Breaks" (6.3MB)

US Patent 5,757,722 and EU Patent EP 0 880 034 A2 (1998), "Method for verifying the location of an array of detectors". A high-order, polynomial regression curve is fitted to a global set of first-arrival pick times as a function of the nominal ranges between a plurality of acoustic sources having known geodetic coordinates and a plurality of acoustic detectors whose coordinates are imperfectly known. The polynomial is applied to the pick times to provide pick time distances with the vertical velocity gradient removed. The known source coordinates, the nominal detector coordinates and the pick times distances are combined to provide a quadratic surface to provide a common data block containing the coefficients for modeling the lateral velocity gradient. Using the so-determined coefficients, the imperfectly-known detector positions are iteratively updated using the Helmert blocking technique.
Download "US Patent 5,757,722"
Download "EU Patent EP 0 880 034 A2"

"Modeling Velocity Gradients in an OBC, First-Break Positioning Algorithm" (1997) was delivered to the European Association of Geoscientists and Engineers. Transverse (vertical, depth variant) and lateral (horizontal, spatially variant) velocity gradients can generate troublesome systematic errors for seismic first-break positioning techniques in Ocean Bottom Cable (OBC) seismic surveys. This paper and presentation with speaker's notes describe two methods of dealing with these problems.
Download "Modeling Velocity Gradients" presentation with notes
Download "Modeling Velocity Gradients" paper

US Patent 5,696,733 (1997), "Method for verifying the location of an array of detectors". A high-order, polynomial regression curve is fitted to a global set of first-arrival pick times as a function of the nominal ranges between a plurality of acoustic sources having known geodetic coordinates and a plurality of acoustic detectors whose coordinates are imperfectly known. The order of the polynomial is chosen to be that order that minimizes the variance of the parameters about the regression curve. The polynomial is used as a quasi-velocity function for iteratively optimizing the best estimate of the ranges between each detector and every source station. The best estimate of the detector position is derived by multi-lateration using the computed ranges.
Download "US Patent 5,696,733"

"Reliability Analysis in Marine Seismic Networks" (1995). This paper describes the application of Delft-method reliability analysis (hypothesis testing using the w-statistic) to the observations and positions of a marine seismic network processed in a Kalman filter that integrates heterogeneous data into a total solution.
Download "Reliability Analysis in Marine Seismic Networks" (6.7MB)

US Patent 5,353,223 (1994), "Marine navigation method for geophysical exploration". The present invention provides a method for on-line real-time processing of navigation data for determining the location of sensor and receiver points in a navigational network having a number of different types of devices. Observations from these devices are obtained using a coordinate system that follows appropriate nominal sailing lines. Outlying observations are discarded using w-statistics for the observations. Any correlated observations such as compass azimuths are uncorrelated. The uncorrelated observations are then sequentially processed in an extended sequential Kalman filter, which provides the best estimate of the station coordinates. These estimated coordinates are then used to determine the location of the source and receiver points.
Download "US Patent 5,353,223"

"Horizontal Midpoint (HMP) Accuracy in Marine Seismic" (1991). The horizontal midpoint (HMP) is the average of the positions of a gun and a streamer reciever. Survey pre-analysis can determine the positional accuracy of vessel, streamers, guns and tail buoys. These assets are connected by gyrocompass azimuths, cable compass azimuths, acoustic ranges, laser ranges, angular measurements, streamer section lengths and GPS devices, all of which have well-known random errors. In this paper I apply Gauss's law of covariance propagation to determine HMP random error and to demonstrate that it is at most the average of gun and streamer error ... and it can be as little as zero!
Download "Horizontal Midpoint Accuracy"