# Questions tagged [geodesy]

Scientific discipline dealing with the measurement and representation of the Earth's shape and gravitational field.

56 questions
631 views

### Local Cartesian (NED) to Geodetic (Lat,Lon,Alt) Conversion - Max Distance from Reference Point

Looking at this: https://www.mathworks.com/help/map/ref/ned2geodetic.html: [lat,lon,h] = ned2geodetic(xNorth,yEast,zDown,lat0,lon0,h0,spheroid)) The obvious question is by how much the current ...
62 views

### Completing Coordinate transformation?

I have two airborne lidar datasets and, for purposes of comparing change between the two, would like to standardize the vertical and horizontal coordinate information for each. The plan is to ...
244 views

### Re-referencing raster in rotated coordinate system by “de-rotating” it

My Trying to define a "rotated regular grid" coordinate system in QGIS question about this got closed because there was already an answer to it, which I understand. I went to the answer in ...
524 views

### EPSG code for a 3D CRS based on WGS84?

I've been searching for an EPSG code for the coordinates I'm working with: geodetic latitude and longitude (not geocentric) and height above the WGS84 ellipsoid. I don't care about coordinate order. ...
65 views

### Calculating Datum Corrections to Overlay pre-NAD27 USGS Maps?

I am working with some older (ca. 1900) USGS Topographic Maps. These Raster maps are georeferenced with a CRS of NAD27 and poly projection (polyconic). However, they are offset and require easting/...
232 views

### Can't get RTKLIB to use an external geoid

I want to write the results of processing a Rinex file using geodetic heights, and an external geoid from Spain's geographic institute IGN. I have downloaded the geoid files from their FTP in text ...
129 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 ...
45 views

### Name for meridians rotated 90 degrees about a meridian

Let's say you drew lines similar to meridians, in that they all intersect at two opposing points--but instead of being at the poles, those points were instead somewhere along the equator. Is there a ...
66 views

### Recommendation for a book for geographical distance calculations [closed]

I am currently writing my Thesis and I need a book covering the geographical distance calculation like haversine and Vincenty. Since I am not of this field, I can't find books which might help me ...
518 views

### Why do we take the inverse of the flattening?

I am new to geodesy and am learning about calculating flattening. I understand that the flattening f is calculated as f=(a-b)/a where a is the semi-major axis and b is the semi-minor axis. I am ...
363 views

### PostGIS Geography Buffer producing different areas?

I'm trying to create circles of equal area in different places, but depending on the location of the centroid different areas are calculated. For example SELECT ST_Area(ST_Buffer('POINT(0 0)'::...
36 views

### Reverse Calculate Ellipsoidal Height

I have a few hundred points with ellipsoidal height taken a few years ago. Based on these ellipsoidal heights I had deduced orthometric heights for the same. Is there a way to find the ellipsoidal ...
425 views

### What's wrong in using latitude and longitude as X and Y on a Cartesian space?

What can go wrong and what kind of error can build up if I use geodetic coordinates as if they were cartesian and place my objects into my world with no conversion formulas?
242 views

### JTS Vividsolutions API: compute First (direct) geodetic problem

I'm using the popular JTS Vividsolutions API for Java. I'm struggling to find if I can perform calculation of the First (direct) geodetic problem with the API. Is there a way to calculate this with ...
108 views

### Strategies and methods that Datums and Coordinate Systems use to account for movement of the earth's surface

Are there datums and coordinate systems that address the issue of shifting coordinates through time? If so, what are some of the strategies and methods that the datums and coordinate systems use to ...
108 views

### Which projection is suitable for the measurements of this great circle?

I have drawn a circle on google earth pro in such a way that its radius starts from earth center 0,0 (lat/long) and ends at 0,90 (lat/long). This circle divide the earth into two equall halfs as shown ...
2k views

### Difference in destination location between pyproj and geopy

I am looking at ways to calculate (in Python) the destination location from a point given bearing and range. Based on the results comparison from the 2 libraries in subject(geopy and pyproj), I ...
39k views

### Is WGS84 a Coordinate system or projection system? [duplicate]

WGS84 is often referred to as a "projection system" and sometimes it is confusing to me about what a "projection system" is and where WGS84 falls in one. Could someone please clear that up for me?
43 views

### Set of intersection points in trilateration / multilateration [duplicate]

Like in this post I will get a set of points (3 or more) with latitude, longitude and distance (in KM) information to find out the target location. A distance could be about 500 KM. The circles (...
68 views

### Open Source Webmaps and Geotiffs

I have recently started to learn how to use open source web maps, and have come across the following issue. When using geoserver and geo explorer (part of the open-geo-suite), I seem to get an ...
728 views

### How to Convert Property Survey Monument Marker Coordinates to State Plane?

I have a set of Connecticut monument locations (a monumented property survey using monuments designated CGS Mon. No. 1577-1580). Their coordinates appear to me to be in meters (244536.84 N, 386409.67 ...
55 views

### Given distance (in meters) what is the angle in geographic reference systems? [duplicate]

In QGIS and other systems sometimes I have a layer in geographic reference system (typically WGS84, EPSG:4326) and I'd like to calculate a buffer of say 5000m around a point. So, given a point ...
2k views

### Does GPS correct for continental drift?

Does GPS correct for continental drift, and if so, how? (I'm mainly interested from the perspective of consumer devices such as smartphones.)
589 views

### Trilateration Calculation Issue

edit I was able to do this following partially from this solution: Calculating intersection of two Circles? I broke it up into 3 groups of intersections AB, AC and BC. Once I had those I took (with ...
440 views

I think I understand the whole rhumb line and great circle idea but I can't seem to find an answer on this question. Suppose I am driving a car (i don't use ship because I don't want to put the ...
125 views

### Calculate geographic position based on azimuth, distance and height [duplicate]

How to calculate the geographic position of an object in sky (Point B)(like an aircraft) from Home Point (Point A) based on only four variables: Lattitude and Longitude at Home Point, Azimuth at ...
153 views

### <#> doesn't give a useful distance [duplicate]

I'm new to postgresql/postgis and trying to measure a distance. So st_distance() may be the most accurate, it's the slowest too (as I've read). I read that one can use geometric (instead of geographic)...
42 views

### Scale on map requires correction coefficient. But why? [duplicate]

I am computing the distance of a map I am getting from ArcGIS' REST services by using a calculator as provided by this answer. In a nutshell, it uses a GeodeticCalculator for distance computation ...
5k views

### Does the NED use geocentric or geodetic latitude?

What kind of latitude does the National Elevation Dataset (NED) use? Geocentric or geodetic or something else? I can't find the information anywhere on their site (http://ned.usgs.gov/index.html) or ...
58 views

### Calculate end point Height above the MSL of the target point given a starting point, distance, azimuth and elevation [duplicate]

We need to find the end point height (from the earth surface) given the start point lat, lon, azimuth (270 deg), distance (500 km) and elevation above the horizon of start point (10 deg). The ...
241 views

### New coordinate system?

I just had my mind blown in answer to my previous question. I was going to rework that question, but decided it makes more sense to ask a new one. I had been converting between ECEF and lat/lon, and ...
627 views

### Why not measure elevation from the center of the earth?

In trying to understand Geoid vs Ellipsoid height, I ran across this page. One of the claims is: Zero elevation as defined by Spain is not the same zero elevation defined by Canada Basically, ...
207 views

### Learning classical geography - recommended literature etc

I've been working in the field of GIS for a few years now, and there are some disciplines of knowledge where I lack a good degree of education. My educational background is that I've studied computer ...
201 views

### Defining a line from geographic coordinate points.

On a flat surface we can define any point on line which passes from point1 (x1,y1) to point2 (x2,y2) via simple trigonometry. How can we do that with latitude and longitude of 2 points? Imagine we ...
820 views

### Intersection between a ray from lat, lon, alt, with pan, tilt and earth's surface

I have a problem that consists of finding the intersection point between a ray from a given lat, lon, alt, that is looking to a given pan and tilt angles and the earth's surface. I need the lat, lon ...
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 ".....
146 views

### What do different realizations of the same datum have in common?

Firstly, am I correct in assuming that the process of determining the shape and the size of the spheroid is independent from the process of determining the origin and the orientation? For example, ...
217 views

### For a non-geocentric ellipsoid, how does the Lat/Long/Ell Ht & semi-major axis & flattening implicitly define the centre of the ellipsoid?

For example if we compare the AGD84 (Australian Geodetic Datum) with GDA94 (Geocentric Datum Australia), the centre of the AGD Datum is 200 metres different to GDA, because it is a best fit to the ...
926 views

### Long range Trilateration from 3 lat, long, range

I've been looking at the following solution to a similar problem Trilateration using 3 latitude and longitude points, and 3 distances However with my problem the 3 points are spread over a large ...
1k views

### How can I use ArcGIS 10.1 to find a geodesic equidistant point defined by three points?

For example, I have coordinates for three base points on a coastline and I need to find the coordinates of the point off the coast which is equidistant from all three. It’s a simple exercise in ...
1k views

### Technique for splitting raster image into tiles

I have written a standalone application which renders a globe similar to GoogleEarth/WorldWind which is currently able to display raster imagery from WMS servers. The native geodesy of this ...
164 views

### How do I account for changing latitude with a spatial filter?

I'm working with data in latitude/longitude grid form in a non-GIS specialised package (MATLAB) and wish to apply spatial filters to it. As this data contains a broad range of latitudes and is ...
250 views

### Which training courses in Geodetics can you recommend?

Can anyone recommend any training courses in geodesy which would cover the following objectives: Case studies on coordinate issues. Overview of geodetic datums, coordinate reference systems and ...
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 ...
710 views

### Trilateration on a Sphere, given 2 points and 2 distances

Given the points: A) N 38° 38.000 W 90° 20.000 B) N 38° 39.000 W 90° 21.000 (I can calculate the distance between the 2 using a spherical earth model as 7710 feet, though it's not particularly ...
380 views

### Trilateration in 3D with signal strengths

I'm having a hard time getting my head around the maths to locate a target in 3D given a number of known points (4 or more) and a value that indicates the signal strength (range 0–100). I've looked ...
5k views

### Local Coordinate to Geocentric

The ultimate question, I need a transformation matrix to take a point in local space representing a roughly 500m x 500m place in New Mexico centered at -108.619987456 long 36.234600064 lat. The final ...
1k views

### How to generate geodesic linestring from two points in C#

I'm looking for a FREE C# class, library or set of functions that will allow me to generate a geodesic linestring (or array of vertices, whatever) from two decimal degree points. I've found ...