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Questions tagged [ellipsoid]

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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Stereographic projection of WGS84 ellipsoid [closed]

According to this source, an optimal projection for small, roughly square areas is the stereographic projection. The wikipedia page of the stereographic projection shows how to convert from spherical ...
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28 views

Underlying distribution of points in an ellipse

I'm attempting to generate both a uniform distribution and a normal distribution of points that fall within an ellipse shape, made from a centre point, semi major and minor and rotation in degrees. I ...
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Great circle distance vs. ellipsoidal model

Suppose I have a javascript function: sortByDistance( a, // Single point b, // List of points method // ellipsoidal or greatCircle ) { // Returns b, sorted closest to furthest from a }...
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1answer
46 views

Bessel ellipsoid definition for LV95 (EPSG:2056)

I recently wrote some code to transform coordinates between WGS 84 and the new Swiss projected coordinate system (LV95 / EPSG:2056). While doing that, I tried to find an authoritative source for the ...
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1answer
61 views

QGIS Identify feature Cartesian area in degrees

In QGIS 3, the identify feature tool automatically calculates area. However, there are two areas: Cartesian and ellipsoid. The first is being calculated in degrees (not wanted) and the second in ...
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1answer
73 views

Creating points along line at ellipsoidal distance

I need to create points along a polyline in QGIS 3 at every 1000m of ellipsoidal distance and have tried several tools, as suggested in other answers: Points along geometry QChainage plugin Convert ...
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Latitude of Earth reference ellipsoid [closed]

I am trying to create a graphic demonstrating the difference between an idealized perfect sphere and the Earth's reference ellipsoid. (I know this is also an approximation, but nevertheless.) To this ...
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1answer
222 views

Calculate ellipsoidal area for a projected layer in PyQGIS 3

I'd like to loop though each feature in a layer and calculate its ellipsoidal area using QgsDistanceArea() in PyQGIS 3. Everything works fine on unprojected layers, but I get strange results when ...
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1answer
180 views

Is distance between lines of latitude same on ellipsoid?

Is the distance between lines of latitude the same for an ellipsoid? I know they are the same for a spheroid and intuitively, I would say it is the same for an ellipsoid but I could not figure out ...
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2answers
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Understanding geodesic envelope?

I've been looking at some various ways to calculate geodesics. One particularly good site collecting load of helpful information, is this one. There you can also find a link to a map that shows a ...
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1answer
346 views

Is kml altitude mode “absolute” equivalent to altitude over WGS84 ellipsoid?

I am working with an aviation software which outputs points with altitudes over WGS84 ellipsoid. Now I want to represent those points in Google Earth, writing a kml file. I know I have to convert the ...
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1answer
665 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 ...
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1answer
198 views

Do latitude/longitude coordinates ever refer to “real” earth, not idealized sphere or ellipsoid?

I'm new to the world of geographic information systems. While trying to learn the basics of spatial reference systems, I wonder whether there is any situation in which we can have latitude and ...
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1answer
573 views

Making ellipse geometry from some known parameters using PostGIS?

How to create an ellipse geometry with postgis from known axis coordinates and peak radius ? From picture below : Point A and Point B is known lat/lon R is a known result of fresnelZone ...
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726 views

Projecting data from 'EPSG:4326' to Lambert Azimuthal Equal Area with PyProj [closed]

I have a list of data points given in lon/lat coordinates, which I want to convert to cartesian ones using pyproj. My dataset refers to Italy, so I was considering using either the Lambert Azimuthal ...
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2answers
175 views

Do different ellipsoids have different location of centre?

I wanted to understand how latitude and longitude of a location change by changing the reference ellipsoid. If the location of centre in 2 different ellipsoids is same, and they differ only in the ...
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QGIS: CRS, ellipsoids and area calculation

I have a doubt about dynamic CRS, ellipsoids and area calculations. I am using QGIS 2.14.0 (still waiting for IT to install 2.14.11...) When I load a polygon table into a new, empty project, it comes ...
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1answer
72 views

Why computing the distance between two ellipsoidal coordinates needs to be iterative?

I have found internal Android code that calculates distance between two spheroidal coordinates. It is complex and it is iterative. Why? Can't this calculation be done in "single shot"? The Java code ...
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1answer
4k views

What are the main drawbacks of the AuthaGraph projection?

The AuthaGraph projection has recently been hyped as the "perfect projection" for a world map, since it (approximately) conserves area, shape and distances. It also tessellates, so that any point can ...
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1answer
198 views

Why inverse flattening is zero in esri prj file for spheres?

I have a prj file which is assumed to have a sphere datum (not ellipsoid). here is the prj file: PROJCS["WGS 84 / Pseudo-Mercator",GEOGCS["Popular Visualisation CRS",DATUM["...
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1answer
343 views

How can I use GK + ETRS89 projected data in QGIS or Proj?

I got a dataset of Hamburg, Germany in so called "Lagestatus 320" (LS320). The metadata describes it as "Gauss-Krueger mit ETRS89 [Lagestatus 320]". Coordinates are like 3565575.3,5936627.0, they are ...
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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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153 views

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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1answer
6k views

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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3answers
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Meaning of “Elevation above surface of 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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1answer
219 views

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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2answers
248 views

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/...
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1answer
848 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 ...
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1answer
1k 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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0answers
116 views

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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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 ".....
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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 ...
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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 ...
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0answers
379 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.
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3answers
540 views

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, ...
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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 ...
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1answer
696 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 ...
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0answers
185 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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1answer
130 views

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 ...
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2answers
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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 ...
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1answer
597 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.
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3answers
21k 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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3answers
253 views

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 ...
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3answers
3k 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-...
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1answer
698 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'...
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1answer
589 views

What is the DNSC08 Mean sea surface model ellipsoid based on?

Does anyone know what Danish Space centre DNSC08 mean sea surface model uses as the reference ellipsoid? there is no meta data on the web site: http://www.space.dtu.dk/English/Research/...
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3answers
935 views

What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation?

I've been musing (and doing prototype coding) for a 'projection free' geographic codebase with your basic point, line & polygon primitives. Rather than dealing with all the sacrifices that come ...