Purpose

• Elevation of points on google map
• EGM96 geoid separation
• Tidal datums using VDatum
• GEOID12B separation usign VDatum

Disclaimer

Not suitable for any survey.

Status

Beta

Method

Uses google map elevation API. Most data probably comes from SRTM. But some location data seems to be from Lidar elevation dataset. Google uses WGS84 and EGM96 (OGC KML 2.2 standard). Hence, elevation is referenced to EGM96 geoid.

Other output data are: EGM96 Geoid Separation; Tidal datum like MLLW, MHHW, LMSL, Geoid separation using VDatum.

NAVD88 ELEV = GEOID12B - h - EGM96

Instructions

1. Click on map to start collecting data
2. Hover or click on icon to read data
3. Use tables to see all data
4. Use CAD to plot points in AutoCAD
5. Use + button to locate user
6. Reset clears all data

Options

• Worldwide data
• For CA State Plane Zone III, additional coordinates x, y feet are available
• Elevation unit conversion and datum adjustment
• Use Group name to identify points
• CAD is for plotting in AutoCAD points x,y,z
• SF elevation is calculated by subtracting 8.15 feet from the LMSL
• Center map to user location

Glossary

CA III : California State Plane III US Survey feet

EGM96 : Earth Gravity Model 1996

LMSL : Local Mean Sea Level

NAVD88 : North American Vertical Datum of 1988

SRTM : Satellite Radar Topography Mission

Limitations

• All limitations of google map elevation api
• Google Elevation dataset is from various sources
• Accuracy is not uniform
• Not suitable for any survey
• Elevation is in metres above Local Mean Sea Level (LMSL)

Resources

1. google map api
2. OGC KML 2.2
3. google data
4. other data sources
5. mean sea level
6. Topography


7. SF Vertical Benchmarks
8. NGS Benchmarks
9. VDatum
10. Conversions
11. SRTM
12. Open Altimetry
13. GEOID EGM
14. GEOID12B
15. CDP Engineers: NAD83 & WGS84 Explanation

Updates

2020 B. Shrestha

2018 B. Shrestha

2017 B. Shrestha