10
votes
Accepted
PostGIS Geography Buffer producing different areas?
Internally, ST_Buffer(geography, ...) uses a fixed projection guess with _ST_BestSRID, which are typically UTM zones or whatever makes sense to the algorithm. This is why you see the differences, ...
- 41.6k
7
votes
Accepted
Difference in destination location between pyproj and geopy
It looks like you've done everything correctly. You can evaluate the errors from each method by performing the inverse calculations to find the distance given the origin and destination coordinates, ...
- 41.6k
7
votes
What datum (reference ellipsoid) does Google Earth use?
The heights on google earth refer to EGM96 and are, therefore, Geoidal heights. The lat/long are referred to the WGS 84 ellipsoid.
- 71
7
votes
Get lat/long given current point, distance and bearing
What follows is a development of the formulas found in the Aviation Formulary by Ed Williams and in Movable Type Scripts by Chris Veness, from the formulas of spherical trigonometry, to solve the ...
- 13.4k
5
votes
Accepted
QGIS Transformations with respect to desired epoch
Make sure you have QGIS compiled against a GDAL/OGR version greater than 3.4:
We can perform the vector transformation with the Convert Format process (you can look it up in the Toolbox even as ...
- 13.4k
3
votes
Accepted
Planimetric Area Measurement in Geographic Projected Vector Data in QGIS3
You are computing ellipsoidal areas (using the $area geometry function in the expression). But changing the reference ellipsoid from WGS84 to a plane.
If you use area($geometry) expression instead, ...
- 13.4k
3
votes
Accepted
Online PPP Services?
You may also use APPS (https://pppx.gdgps.net/)
It's a technology from NASA's Jet Propulsion Laboratory and they use there own GipsyX/RTGx software for processing the GPS measurements.
3
votes
Local Cartesian (NED) to Geodetic (Lat,Lon,Alt) Conversion - Max Distance from Reference Point
I don't think there are practical limitations to ned2geodetic.
The conversion from LLA to ECEF coordinates has closed form solution.
The rotation of NED vector to ECEF has closed form solution.
...
- 31
3
votes
Accepted
EPSG code for a 3D CRS based on WGS84?
EPSG/WKID number 4326 relates to WGS84 Geographic, with units in degrees. The ellipsoid is extremely similar to GRS80, with only a slight difference in one of the axes. This is the code and system ...
- 2,588
3
votes
Difference in destination location between pyproj and geopy
The geopy pull request fixes your issue with geopy. You will need to
install the python package geographiclib first with
pip install geographiclib
- 3,201
3
votes
Accepted
What's wrong with using latitude and longitude as X and Y on a Cartesian space?
Everything really. Distances will become meaningless. Areas will become meaningless. Hence all outputs such as slope will become problematic. As you move in latitude then your "grids" will appear to ...
3
votes
How do you compute the earth's radius at a given geodetic latitude?
Interesting to find that my math illiterate solution did the job with 5 minutes of thought and coding, wouldn't the flattening factor have to be considered rather than a perfect elliptical model?
...
3
votes
Accepted
Adding EPSG:7019 (GRS 1980) to PostGIS
GRS 1980 is defined by two measurements:
Semi-major axis = 6378137
Inverse flattening = 298.257222101
With this, you've defined an ellipsoid, but you do not have a coordinate system. Where is Europe ...
- 5,368
2
votes
Moving dead ahead: rhumb line, great circle or none
I know the question has answered already, but allow me to show you something cool for future use:
A live Google map where you can move the edge markers affecting the great circle and rhumb line same ...
- 21
2
votes
Which of EGM96 geoid or WGS84 ellipsoid fits the earth better?
The answer depends on what you are interested in and therefore what you mean by 'earth's surface'. The Geoid is the equipotential surface (in terms of gravitational potential). The ellipsoid is a ...
- 109
2
votes
JTS Vividsolutions API: compute First (direct) geodetic problem
I would much rather suggest doing it manually since the math is simple. This will be much faster than using so many potentially complex methods.
public static Point createPointInDistanceAtAngle(Point ...
- 10.2k
2
votes
Accepted
Recommendation for a book for geographical distance calculations
One place to start is the bibliography provided by the geographiclib of Charles Karney.
This starts at the begining with:
I. Newton, Philosophiae Naturalis Principia Mathematica (3rd edition,
...
- 79.9k
2
votes
Can't get RTKLIB to use an external geoid
You are missing the out_geoid option. My working file looks like:
...
out-height =geodetic # (0:ellipsoidal,1:geodetic)
out-geoid =egm96 #(0:internal,1:egm96,2:egm08_2.5,3:...
- 1,609
2
votes
Do different ellipsoids have different location of centre?
If two ellipsoids share the same origin and axes (both use Greenwich and the same North pole), but have different axes lengths, only the geodetic latitude will change between the two. This is true ...
- 18.7k
2
votes
What's the name of the area between two geographic coordinates?
A quadrangle?
Yes, it is named: spheroidal quadrangle.
- 13.4k
1
vote
Are Tissot's indicatrices enough to tell whether or a not a projection will keep 3D lines also straight in the projected 2D space
A cartographic projection is a nonlinear transformation in two dimensions.
So in the first place you must reduce the three-dimensional line to the mathematical surface on which the cartographic ...
- 13.4k
1
vote
How does Google Earth calculate the inverse geodesic problem, in particular the forward azimuth?
After two days I found the answer to that question myself. . I am not sure if I should just delete my post or leave it there together with this answer. Well, maybe someone else wants to know too.
...
1
vote
Accepted
Derivation of initial bearing calculation
I was surprised that I didn't find this ready-made question and answer on this site.
This formula is sometimes taken from http://www.movable-type.co.uk/scripts/latlong.html, which in turn is taken ...
- 13.4k
1
vote
Accepted
What's the name of the area between two geographic coordinates?
More informally than a spherioidal quadrangle, a much more common and useful term is "bounding box", sometimes shortened to "bbox".
- 8,598
1
vote
Accepted
Calculating bearing (magnetic) between two lines?
Yes, there is something more to consider: the Magnetic Declination.
This is a scalar variable, derived from a physical property: the Earth's magnetic field.
It is variable dependant to location and ...
- 13.4k
1
vote
Height transformation parameters between any model and EGM-96
If you have a geoid model, that is often a set of equations to convert between gravity-related heights (elevations) and ellipsoidal heights. It's often modeled as a grid file. There are both versions ...
- 18.7k
1
vote
Accepted
Name for meridians rotated 90 degrees about a meridian
They are oblique meridians, perpendicular to an oblique equator.
- 8,858
1
vote
Accepted
Calculating Datum Corrections to Overlay pre-NAD27 USGS Maps?
Prior to NAD27 / North American Datum of 1927, US maps used the US standard datum AKA USSD. Starting at NADCON 5.0, the National Geodetic Survey (NGS) has started supporting transformations to and ...
- 18.7k
1
vote
PostGIS Geography Buffer producing different areas?
If your data is in a geographic coordinate system, rather than a cartesian system, your buffers could vary in area due to the shape of the Earth.
58 square kilometers in area difference may be ...
- 1,317
1
vote
What's wrong with using latitude and longitude as X and Y on a Cartesian space?
Latitude and longitude are not linear measures, and a planar calculation of distance using them will yield nonsense results. Although lines of latitude, or parallels, are evenly spaced, and could be ...
- 3,862
Only top scored, non community-wiki answers of a minimum length are eligible