TAG: David B. Zilkoski

A look at NGS’ GPS on benchmarks program in Alaska

April 5, 2017By
GPS_World_Newsletter_12_Fig_1-medium

The last column, February 2017, focused on addressing the following questions: (1) Is the large GPS on benchmarks residual due to an issue with the NAVD 88 orthometric height or the NAD 83 (2011) ellipsoid height? and (2) Should stations with large GPS on benchmarks residuals be included in the development of NGS’ hybrid geoid models? The column provided suggestions... read more

This article is tagged with , , , and posted in Opinions, Survey

Establishing orthometric heights using GNSS — Part 11

February 1, 2017By
Figure 1 – GPS on Bench Marks Residuals using GEOID12B computed using NGS GPS on Bench Marks Shapes/rasters

Strategically Occupying Stations to Support NGS’ GPS on Bench Marks Program This is the 11th segment in my series on “Establishing Orthometric Height Using GNSS.” Each column has focused on a specific topic and provided procedures and tools for analyzing that topic. The columns are meant to build on each other. When addressing a topic that has been discussed in... read more

This article is tagged with , , , and posted in Opinions, Survey

Establishing orthometric heights using GNSS — Part 8

August 3, 2016By
Figure-2-T

Upcoming Survey Scene newsletters will carry additional columns in this series. Basic procedures and tools for determining valid published NAVD 88 GNSS-derived orthometric heights for constraints These columns have provided the reader with basic concepts, routines and procedures for understanding, analyzing, evaluating and estimating GNSS-derived ellipsoid and orthometric heights. In my last column, Part 7 (June 2016), we analyzed the changes in adjusted heights... read more

Establishing orthometric heights using GNSS — Part 7

June 2, 2016By
Figure 1. Leveling Network Design Used in the General Adjustment of the North American Vertical Datum of 1988 (Figure 3 from the report).

Basic procedures and tools for determining valid NAVD 88 heights for constraints To date, the six parts of “Establishing Orthometric Heights Using GNSS” have provided the reader with basic concepts, routines and procedures for understanding, analyzing, evaluating and estimating GNSS-derived ellipsoid and orthometric heights. In Part 5 of this series, we discussed National Geodetic Survey’s NGS 59 guidelines and methods for evaluating the results... read more

Establishing orthometric heights using GNSS — Part 6

April 6, 2016By

Basic procedures and tools for ensuring GNSS-derived orthometric heights meet the project’s desired accuracy To date, this series of columns has addressed the following topics: basic concepts of GNSS-derived heights, National Geodetic Survey’s (NGS) guidelines for establishing GNSS-derived ellipsoid heights (NGS 58), differences between hybrid and scientific geoid models, procedures and tools for detecting GNSS-derived ellipsoid height data outliers, and basic... read more

Establishing orthometric heights using GNSS — Part 4

December 2, 2015By

Part 1 of this series appeared in the June Survey Scene newsletter, Part 2 appeared in the August newsletter, and Part 3 appeared in the October newsletter. Upcoming Survey Scene newsletters will carry additional columns in this series. Basic Procedures and Tools for Ensuring GNNS-Derived Ellipsoid Heights Meet the Project’s Desired Accuracy In Part 1 of this series, I discussed the basic concepts of GNSS-derived... read more

Establishing Orthometric Heights Using GNSS — Part 3

October 7, 2015By
A depiction of the United States geoid. Areas in yellow and orange have a slightly stronger gravity field as a result of the Rocky Mountains.

Part 3 describes the differences between a scientific gravimetric geoid model and a hybrid geoid model, and why it is important to use both geoid models in your analysis. read more

Establishing Orthometric Heights Using GNSS — Part 2

August 5, 2015By
Figure 2. NAD 83 (2011) Network Design for Stations EA0873 and EA0875. [Note: GNSS Vectors for GNSS projects GPS 1588 and GPS 2057 were provided by NGS].

GNSS-derived ellipsoid heights are the basis for GNSS-derived orthometric heights, so it makes sense to make these ellipsoid heights as close to error free as possible. This article will discuss guidelines for detecting, reducing andr eliminating error sources in ellipsoid heights. It will focus on guidelines for establishing accurate ellipsoid heights in a local geodetic network. (Part 2 of a series) read more