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Questions tagged [geoid]

The hypothetical, natural, surface of mean sea level for the whole Earth. An equipotential gravitational surface. The datum for orthometric heights.

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Understanding Google Earth Pro ruler tool algorithms?

When using Google Earth Pro ruler (Tools / Ruler or by clicking on the "ruler" icon), the ruler tool tells us the heading from one point to another which is not the same as that obtained by Karney's ...
3
votes
2answers
410 views

Where does the Geoid information in a GPS unit come from?

In the NMEA GGA-message the 11th field is Geoid separation. How does the GPS-unit "know" this separation? Are GPS units preloaded with an EGM (Earth Gravitational Model)?
4
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1answer
54 views

Using NAVD88 geoid in Northern Canada?

The USGS NED (1-arcsec) dataset is available for the continental US as well as most of Canada. It is based on the NAVD88 vertical datum. I am interested in using the DEM to orthorectify SAR scenes in ...
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1answer
53 views

Adding local geoid in ArcGIS Desktop?

My vector data is based on EGM2008 and I want to add local geoid to arcgis and project vector data from EGM2008 to local geoid. If it is not possible to add custom local geoid in arcgis, how can I ...
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0answers
77 views

Adding GDA2020 NTv2 transformation to ArcGIS 10.5

The implementation of GDA2020 is drawing near! In an effort to be ready before time I have downloaded the NTv2 Grid Shift Binary (GSB) transformation grid from ISCM (available here) who are the ...
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0answers
21 views

What surface's area is used to compute area of country? [closed]

Premise: Earth's surface geometry is modelled by means of different geoids -depending on the objectives. The roughest and most basic are ellipsoids surfaces. Yet, on a small scale, e.g., area of ...
0
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1answer
416 views

Using local mean sea level (LMSL) as altitude for converting latitude longitude altitude to ECEF

I am new in Geographic area and would like to convert latitude and longitude coordinates into ECEF x,y coordinates so that I could do some linear calculation of line or circle equation. I was able to ...
3
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1answer
298 views

How to calculate the distance to the Earth center if I know the elevation above the reference geoid?

How could I calculate this? Should I simply add it to 6371km?
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1answer
365 views

Seeking Trimble GGF Geoid File Format Specification?

I want to generate Trimble GGF Geoid files from my software. Can anyone provide me with a format specification for the binary ggf files used by Trimble? I found a basic description on the ...
1
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1answer
96 views

Downloading geoid chgeo2004?

Does anyone know where I could download geoids? Specifically I need the Swiss Geoid CHGeo2004. I found this link: https://opendata.swiss/de/dataset/geoidmodell-chgeo2004-in-ch19031 But it only ...
0
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0answers
393 views

Converting elevation from EU-DEM (ETRS89) to WGS84

I'm having a hard time trying to use elevation data from EU-DEM. This data is in ETRS89 (EPSG:4258), according to their site. Now, when I extract the elevation for a shore, I get 0 meters of ...
2
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2answers
1k views

Convert Geoid File Types

Anyone know what I can use to convert a geoid surface stored as , BYN into .GTX for use with PROJ4? The CCG2013A vertical datum and geoid model from NRCan is only available, as far as I can find, in ...
6
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1answer
638 views

Converting LiDAR ellipsoidal heights to orthometric heights?

Is there any tool to convert all Z attributes (ellipsoid h) value into orthometric height (H)? The idea is, having a point cloud (.las) and geoid undulation EGM08 (.asc) get a point cloud (.las) with ...
2
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0answers
632 views

Correcting incorrect altitudes of points recorded by my Android or how to calculate Geoid Height in QGIS

I tried to edit my question with more details and I also think that lot of people can benefit from this question! I was recording a track with my Android and later I found out that I end up having ...
2
votes
1answer
84 views

What is elevation relative to in EPSG:2284?

I have some locations in EPSG:2284: (3669486.63386,11293013.10592,709.08004), (3669559.13811,11292972.72831,711.60055), (3669639.51308,11292851.48264,712.22258), (3669800.62304,11292949.38118,714....
6
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2answers
341 views

Are LiDAR datasets with same vertical datum, but based on different geoids comparable?

I have two sets of LiDAR for the same region that I would like to compare. Both are in NAVD88. The older LiDAR set used GEOID03 for the transformation. The newer LiDAR set used GEOID09 for the ...
1
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1answer
106 views

How does Ellipsoidal Height and Geoidal Height impact water flow? [closed]

I see this as a common theme Ellipsoidal height doesn't dictate water flow. Take a shot at explaining this. I think I understand this but it sounds like it would be of use to have a question about ...
2
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1answer
311 views

How does a Spatial Reference System change the underlying geoid without having to update coordinates?

Reading Wikipedia on WGS84 I see this, Currently, WGS 84 uses the EGM96 (Earth Gravitational Model 1996) geoid, revised in 2004. This geoid defines the nominal sea level surface by means of a ...
7
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4answers
771 views

How does a Spatial Reference System like WGS84 have an elipsoid and a geoid?

I found out that WGS84 is an ellipsoid with a "geoid component", but I'm unsure exactly how that can be. This is from PostGIS in Action, Second Edition (pg. 64), but it seemed a bit vague. ...
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0answers
42 views

What is Considered in Geoid?

I found contradictory sources for what's considered in geoid and can't decide on either side because the sources seem about equally reliable. In particular, the question I'm asking is whether ...
6
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3answers
2k views

Vertical Datum conversion of a raster with gdal

Is there a tool available in gdal to do vertical datum conversion of a raster DEM? I'm looking for a single command line to execute the vertical datum conversion of a raster like the las2las of Liblas ...
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0answers
89 views

What geoid does WGS 72 use?

I see from the WGS Wikipedia article: Currently, WGS 84 uses the EGM96 (Earth Gravitational Model 1996) geoid, revised in 2004. I see there is an older EGM84 geoid but I couldn't find anything ...
4
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2answers
1k views

Find gravity normal by ECEF or GPS coordinate of point

How to find gravity normal by ECEF or GPS coordinate of point? Is it the same as normal to elipsoid? Is this ordinary way to calculate normal to ellipse? I'm not quite sure which altitude is GPS ...
2
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1answer
207 views

How to georeference city data set with geoid and objectid as only location data

I am new to Cartodb and ran into my first hiccup. I was trying to import a data set of walkable food access in Philadelphia that is available from Open Data Philly. I can't figure out how to ...
3
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2answers
2k views

How to convert the SRTM DEM orthometric to ellipsoidal heights using ArcGIS or others GIS?

Recently I got the SRTM DEM from Cgiar,which based on WGS84/EGM96. and I merged the tiles to one tiff file. I want to get the WGS84 ellipsoidal heights. According the steps from the Arcgis Help 10.2 ...
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0answers
140 views

How can I calculate the intersection of a line and the geoid (EGM96)? [closed]

I have a known line (point and vector) described in ECEF (Earth-Centered, Earth-Fixed) coordinates and I need to find where it intersects the geoid (Earth Gravitational Model 1996). Is there existing ...
3
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1answer
222 views

Is there a method to tell which hemisphere a point belongs to, in WGS84 geoid, where the equator is an arbitrary ellipsis?

I use the WGS84 geoid (because I'm working with a GPS chip). I define an ellipsis that splits the surface in two parts, lets name these 'A' and 'B'. This ellipsis is defined by two points 'a' and 'b'...
5
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2answers
698 views

What programs would allow for the mapping of a geoid in 3d?

I would like to find a method for plotting an exaggerated geoid (e.g. topography): I primarily use R for my work but would be interested in other open source software options (e.g. QGIS w/ GRASS). I ...
3
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2answers
2k views

How do you convert SRTM HGT elevations from WGS84 into meters above sea level?

I am building a JavaScript script that reads binary HGT files - as generated by the SRTM - and converts the data into bitmaps viewable in your browser. You can try out the script and view the source ...
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1answer
89 views

Is it due to irregularity of geoid, we cannot convert the height between spherical datum and local datum by cs2cs?

Is it due to irregularity of geoid, we cannot convert the height between spherical datum and local datum (which uses locally defined geoid and height) by cs2cs? What I mean is that, by using cs2cs, ...
2
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1answer
3k views

Which of EGM96 geoid or WGS84 ellipsoid fits the earth better?

ImageCredit Question If we separately add up |H| and |h| over the earth surface, which of the sums come out smaller? Background There is a phrase in the tag description of "ellipsoid" that says ".....
3
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4answers
3k views

“Horizontal” and vertical datums terminology

I have heard people referring to as a horizontal datum to models such as WGS84 and as a vertical datum to geoids. The former is primarily used for determining latitude and longitude but also the ...
5
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1answer
1k views

Can GDAL Perform Vertical Transformations?

Can GDAL perform vertical transformations? If the answer is yes, please indicate which amongst these listed pages can explain how exactly to accomplish vertical transformations? If there is some ...
2
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0answers
368 views

How do you compute vertical transformations in QGIS?

How do you compute vertical transformations in QGIS? Ideally, the procedure / plugin will allow the loading of sundry geoid models.
2
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0answers
391 views

Height of the geoid in ECEF coordinates

I know that the relationship of geoid height N and ellipsoid height h to orthometric height H is defined by H = h - N, but what if I have some position in Earth-Centered-Earth-Fixed (ECEF) coordinates?...
26
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3answers
1k views

Are ellipsoids a mathematical necessity?

The literature usually just tells us that the Geoid is too complex to describe mathematically and that we therefore fit different Ellipsoids to approximate it. Are these Ellipsoids mathematically ...
5
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3answers
3k views

Specification for US Census GEOID?

I'm writing a program that needs to generate GEOID values from 2000 and 2010 Census data, to link the census data to TIGER/Line records. I'm starting with the state, county, region block, etc, values ...