# Tagged Questions

An ellipsoid is a closed quadric surface that is a three-dimensional analogue of an ellipse. In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.

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### 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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### Convert EGM96 gps elevation to WGS84 ellipsoid elevation.

I have GPS elevation data (300k points) in EGM96. These points are located on the East US coast. I realise i need to work out the difference between the EGM96 and WGS84 ellipsoid in this region to ...
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### from/to ellipsode to/from cartesian conversion

i am trying to convert from/to ellipsoidal coordinates (lat,lng,alt) to/from cartesian(x,y,z) i wrote the below code to do the conversion, but given the initial values of the gpsLat and gpsLng i ...
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### Difference between datum and ellipsoid for geodetic coordinates?

Looking at the Wikipedia page for the North American Datum, it seems to imply that the datum is completely defined by the ellipsoid, which defines the major/semi-major axes, flattening, etc. For ...
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### What is the meaning of “Elevation above the surface of the ellipsoid”?

I'm using implementation of Vincenty's algorithms, and I have their class called "position" that requires lat, lon, and elevation defined by: "Elevation above the surface of the ellipsoid". What is ...
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### A point due east of me is closer to the equator? [duplicate]

This footnote: East-west directions can be misleading. Point B, which appears due East from A, will be closer to the equator than A. Thus the curvature found this way is smaller than the curvature ...
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### QGIS Cross Section Profile Distance using Ellipsoid?

I am working with QGIS 1.8 and 2.6 and can't get any of the Cross Section Profile tools to provide the ellipsoid ("proper") distances. All the distances use geographic coordinates which are too long/...
356 views

### How can I get the circle of a sphere (on Earth ellipsoid) around a point using the Latitude and Longitude?

Specifically finding points along the circle. If possible without converting into Northing/Easting beforehand. I'm looking for the fastest possible way to calculate points in Latitude/Longitude in a ...
669 views

### Converting Lambert Conformal (x, y) of spheroid to (lon, lat) of NAD83 with proj/cs2cs?

Revised Trial: Correct? According to Andre Joost advice, I tried with "+towgs84=0,0,0", and the both two ways seem to get the same answer that mkennedy posted below. So, just to make sure, anybody ...
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### Are ellipsoid and datum the same? [duplicate]

Are the datum and the ellipsoid the same? What is a Datum? The Earth is shaped like a flattened sphere. This shape is called an ellipsoid. A datum is a model of the earth that is used in mapping....
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### 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 "...
1k 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 ...
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### 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 ...
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### 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.
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### What is the precise distance from equator to pole according to WGS84?

For calculating areas of polygons by means of projecting to a cylindrical equal area projection I came across the following discrepancy: I ended up with a different distance, off by more than 5km, ...
298 views

### Why does the buffer tool keep producing ellipsoid when I want a circle?

I want to create a 50 mile radius around a point. I've got the point as a layer. I've run the buffer tool found in Vector -> Geoprocessing Tools and set the distance to 0.5. Every time I run the ...
1k views

### Bearing/Course/Heading in WGS84 ellipsoid model

There is a common formula for computing the initial bearing for a course from lat1, lon1 to lat2, lon2. (And yes, I'm aware that the course will change when traveling). atan2( sin(lon2-lon1) * cos(...
651 views

### Are ellipsoids a mathematical necessity?

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

### How to determine error radius of given points

I am running QGIS 1.8.0 on a 64-bit Windows 7 platform. Given multiple points with different (but close) coordinates, how do I automatically create a new point that programmatically takes into ...
123 views

### is ellipse inside ellipse in WGS84 ellipsoid

My question is quite clear: Assume that there is an ellipse, namely EL1. Parameters of the ellipsoid are (focus11 [latitude, longitude], focus12[latitude, longitude], radius1). And a second ellipse, ...
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### How to fix PJ_healpix.c in PROJ.4?

Michael Speth and i are in the process of fixing the PROJ.4 implementation of the HEALPix map projection (see http://trac.osgeo.org/proj/browser/trunk/proj/src/PJ_healpix.c for the current buggy ...
7k views

### How are EGM96 and WGS84 related to each other?

As far as I understand the EGM96 defines the Geoid, where as the WGS84 Standard defines the Ellipsoid. Is the ellipsoid defined in the WGS84 standard defined in a way to maximize the congruency with ...
493 views

### What datum (reference ellipsoid) does Nasa Worldwind use?

What datum (reference ellipsoid) does Nasa Worldwind use? I can't seem to find where Nasa Worldwind tells explicitly what datum they use. I need some sort of valid link.
10k views

### What datum (reference ellipsoid) does Google Earth use?

What datum (reference ellipsoid) does Google Earth[1] use? I can't seem to find where Google Earth tells explicitly what datum they use. I need some sort of valid link. [1] The default free version ...
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### What's a term for Sea Level Distance which is usable by novice users?

I've been using the term Sea Level Distance to describe the total length of a line string where I ignore the elevation and just calculate the distance from point to point along the ellipsoid and sum ...
913 views

### How to get the height according to EGM96 for a point?

For a program I have to calculate the height according to EGM96. I found http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html - this site delivers files with parameters and a fortran-...
363 views

### Accuracy of planimetric geometry vs. ellipsoidal model

I'm examining the two geospatial options for IBM's DB2 database. In particular I am interested in the accuracy between these two options and whether it's worth it (the more accurate representation isn'...