Hot answers tagged

30 votes
Accepted

Is re-projection needed from SRID 4326 (WGS 84) to SRID 4269 (NAD 83)?

Well, technically, NAD83 is not a subset of WGS84. If you mine further in the SpatialReference.org projetion definitions, you can see the difference between the two projections. PROJ.4 definiton of ...
  • 4,458
22 votes
Accepted

Is the Geometry(4326) an alias for Geography datatype?

tl;dr: No. But see the update at the end. GEOMETRY and GEOGRAPHY are different PostgreSQL TYPES; exposed as higher level (SQL), user-defined composite types to the psql environment, but implemented ...
  • 25.1k
20 votes

Is WGS84 a Coordinate system or projection system?

So there are two pieces to what someone might call a Coordinate System The first is a Geographic Coordinate System or GCS, which is what WGS84 falls under. The definition given by ESRI states that a ...
  • 651
19 votes

What is CRS:84 projection?

Actually it's equivalent to EPSG:4326 but changing the axis from Lat-Long to Long-Lat. The standard EPSG:4326 is Lat-Long
18 votes
Accepted

Changing shapefiles from geographic (WGS84) to projected (EPSG:2263) coordinate system using QGIS

This answer has four sections: What you should do to solve the problem and what you should avoid An example to better illustrate why assigning CRS and reprojecting are not the same An analogy that ...
  • 45.1k
16 votes

What causes the GPS offset/shift in China?

The problem is poorly documented by authoritative sources for English speakers, despite affecting millions of people on an everyday basis. I've spend the past two days trying to understand the ...
14 votes
Accepted

Converting between wgs84 and nad83

Typically, NAD83 and WGS84 are within one meter of each other. Your concerns about differences of 2.5 feet, which are less than a meter, indicate you do need to perform this datum transformation. ...
  • 68.1k
13 votes
Accepted

Merge geojson polygons with WGS84 coordinate

You can use Mapshaper for this, and then dissolve from the command line: mapshaper --dissolve -i your_data.geojson
  • 772
12 votes
Accepted

How does QGIS calculate distances when the data is not projected (WGS84)?

Have a look under the "Project Properties" dialog. QGIS will use the project's settings for ellipsoid when calculating distances in a degree based coordinate system. If you're not using OTF ...
  • 26.5k
12 votes
Accepted

What is meant with EPSG:4326 projection

You've got a good grasp of it. EPSG 4326 (i.e. WGS 84) is not a projection. But if you don't associate a projection to this geographic coordinate system, and naively render the coordinates as x/y ...
11 votes

What are the map units that WGS84 uses?

Be careful as WGS84 is a bit ambiguous. Most of the time it mean EPSG: 4326 that is indeed in degrees (and the base of GPS position) but the name WGS84 could be used for other CRS with different unit ...
  • 12.5k
10 votes

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

WGS84 is natively XYZ, like the International Terrestrial Reference Frames (ITRF), and you can use an ellipsoid model to convert to latitude, longitude, and ellipsoidal height. Ellipsoidal heights ...
  • 18.3k
10 votes

Converting resolution in degrees to resolution in meters

Easiest way is to convert the raster to a projected system, and get the cell size directly in meters. That not being possible, or desirable, you can still convert lat/lon values to metric values, but ...
9 votes
Accepted

Projected coordinate system for South America

You first need to decide what distortion properties would you like to control for. That is to say, are you interested in preserving area, distance or shape? There is a decision support tool for ...
  • 50.6k
8 votes
Accepted

R: Return the UTM zone that a WGS84 point belongs to

Each UTM zone is 6 degrees wide, so you can get the zone number by looking at the longitude: floor((longitude + 180) / 6) + 1 This assumes that you have longitude within [-180.0, 180.0).
  • 40.3k
8 votes

Why does Pyproj fail converting lon lat alt to ECEF?

Probably because in lon, lat, alt = 49.74761271, -113.2179781, 0 a lat of -113.2179781 is outside the valid bounds of -90 to 90.
  • 12.5k
8 votes

Generating polygon representing rough 100km circle around latitude/longitude point using Python?

I think I've found a working solution, using the Python geog library: https://pypi.python.org/pypi/geog import numpy as np import json import geog import shapely.geometry p = shapely.geometry.Point([-...
8 votes
Accepted

Generating polygon representing rough 100km circle around latitude/longitude point using Python?

An alternative solution would be to create a local metric projection and create the buffer in that projection. https://shapely.readthedocs.io/en/stable/manual.html#other-transformations tells you how ...
  • 8,847
8 votes
Accepted

Why is the length of one degree in Turf 0.9988?

This seems to be the end result of an interesting conversion from radians to degrees. t.convertLength(Math.PI,"radians","degrees") 179.78993435469053 PI radians should be 180 degrees. Looking at the ...
  • 54.3k
8 votes
Accepted

QGIS 3.6.1 problems with CRS

Following on Ian Turton's comment... Prior to performing ANY geometry calculations or analysis on a layer(s), the layer(s) MUST be 1) projected to the desired CRS, and 2) that CRS must be the same for ...
  • 7,180
8 votes

What is MHHW Mean Highest High Water, in terms of datums/coordinate systems?

Mean Highest High Water is a reference surface corresponding to the height of high tides, averaged over a certain period of time (usually 19 years, a value close to a Metonic Cycle and a Lunar Node ...
  • 3,686
8 votes

Use ST_DWithin on WGS84 geometry data

The problem is that you are using ST_DWithin on GEOMETRY objects with coordinates in WGS84. Therefore, your function call is requesting all features within 500 degrees (i.e., everything on the planet)....
  • 903
7 votes
Accepted

Should geometries be drawn using rhumb-line or great-circle paths?

PostGIS computes its intersections (and distances (and areas)) differently depending on your column type. if the type is "geometry" the assumption is you want to work on a plane, so you get "straight ...
  • 19.5k
7 votes
Accepted

Projecting shapefile with unknown CRS to WGS84 using QGIS?

The linked kml file seems to contain valid degree coordiantes, but fails to open in QGIS. If you follow the source given in your link to http://www.ecaidata.org/dataset/spanish-and-mexican-land-...
  • 75.4k
7 votes
Accepted

Where to get world-map images for use in webglearth

You may check http://vterrain.org/Imagery/WholeEarth/ for links to satellite imagery, or http://www.naturalearthdata.com/downloads/10m-raster-data/ for raster images. These images can be tweaked in ...
  • 1,513
7 votes
Accepted

Why is my coordinate notation different?

I'm not really sure but maybe check if you meant EPSG 4326 instead of 3857.
  • 638
7 votes

Which is the most accurate method of measuring distance?

Let me focus just on the question of the most accurate way to determine distances on the WGS84 ellipsoid. The accuracy of Vincenty's method is about 0.1 mm providing it converges. It fails to ...
  • 3,096
7 votes

Converting WGS84 to ECEF in Python?

Here is a test(seems both methods work with same precision): import math import pyproj coords = [ (37.4001100556, -79.1539111111, 208.38), (37.3996955278, -79.153841, 208.48), (37....
  • 601
7 votes
Accepted

Difference between X,Y and Latitude,Longitude or Meters

For coordinates captured using a GPS, or by any means, longitude is the X value and latitude is the Y value. These are for a geographic coordinate system and have units of degrees. Alternatively ...
  • 64.2k
7 votes

Reprojecting EPSG:3412 to EPSG:4326 using GDAL?

According to spatilreference.org, your proj4 string is not correct. -a_srs defines the projection but does not modify the coordinates, so your output vrt file is likely to be incorrect (based on a ...
  • 48.8k

Only top scored, non community-wiki answers of a minimum length are eligible