Tagged Questions

WGS84 is a geodetic coordinate system, the World Geodetic System 1984 (EPSG:4326).

12k views

How do you compute the earth's radius at a given geodetic latitude?

(I see there is an equation on wikipedia that does exactly what I am asking but there is no references. I have no way of confirming the validity of this equation!) I already understand the difference ...
14k views

Map projection in OpenLayers

I want to overlay some data whose projection is WGS-84 on Google map layer in OpenLayers. But I just can't make them in the right place. I did as follows: map = new OpenLayers.Map('map', { ...
4k views

What causes the GPS offset/shift in China?

I've spent close to two full days trying to understand the nature of the infamous GPS shift in China. After sifting through the noise, two recurring symptoms are that: GPS coordinates (WGS-84) plot ...
12k views

Converting X,Y coordinates to lat/long using pyproj and Proj.4 returns the wrong coordinates

I'm writing a python script that reads multiple XML files containing x and y coordinates and combines them all into a single csv file. Latitude and Longitude are required fields in the csv, but I am ...
4k views

How is EPSG:4326 data 'projected' in a 2D map?

I like to think I'm relatively well-versed in datums, projections, and coordinate reference systems, so if this is a stupid question I will suffer eternal shame. OpenStreetMap data is stored in WGS84 ...
10k views

What is the projection of WGS84 in GIS software?

WGS84 is a reference ellipsoid that determines coordinates of every point on Earth using latitude, longitude and height about the its surface. This ellipsoid is often used as a base to make maps. ...
1k views

OSGB36 to WGS84 reprojection 'error'

First off, I am a recent convert to QGIS and am greatly impressed with its ease of use and speed compared with the ESRI products with which I am more familiar - my congratulations and thanks to its ...
7k views

Characteristics of different methods to convert ECEF to LLA

I'm trying to convert ECEF (Earth Centered, Earth Fixed) coordinates, which are defined in X,Y,Z, centered at (0,0,0) to LLA (Latitude, Longitude, Altitude). There are a couple of methods I found on ...
1k views

I have done a ton of research on the most accurate transformation to use in mainland Alaska to convert between the NAD83 and WGS84 datums, but I just can't seem to find a definitive answer. ArcMap ...
1k views

Which UTM zone to use for a large country?

I want to reproject OpenStreetMap roads data from the current projection (WGS 84) to UTM, since I read in another GIS.SE discussion (How to get \$length in meters in QGIS?) that WGS 84 cannot be used ...
5k views

java vividsolutions jts wgs-84 distance to meters

my (java) project uses com.vividsolutions.jts.geom, which provides a distance function. After some googling I finally found that the return value from this function is in central angle degrees, when ...
930 views

What's the best projection for rasterization of random latitude and longitude data in the northern Atlantic?

I have a dataset in the WGS84 geographic coordinate system that I would like to interpolate along a grid using Python. It appears gdal_grid is not available through the Python bindings, so I plan to ...
574 views

Find intercept WGS84 coordinates between two segments defined by (Lat1-Long1 and Lat2-Long2) and (Lat3-Long3 and Lat4-Long4)

I need to determine the WGS84 coordinates for a point that is defined by the interception of two segments represented by two sets of WGS84 coordinates each (lat1-long1, lat2-long2) and (lat3-long3, ...
14k views

Converting projected geoTiff to WGS84 with GDAL and Python

Apologies if the following question is somewhat stupid, but I am only VERY new to this whole GIS thing. I am trying to convert some projected geoTiff images to WGS84 using gdal in python. I have ...
1k views

How to find ring of coverage of GPS Satellite on WGS-84 ellipsoid?

Given the following: Time, t The set of IS-200 Ephemeris data, E, of a GPS Satellite corresponding to time t The ECEF position of the GPS satellite, P=(x,y,z), derived from the time and ephemeris, (...
3k views

Looking for a pythonic way to calculate the length of a WKT linestring

I was quite unsatisfied with Calculating Length of Linestrings in WGS84 in Miles. It kept me wondering if there is a more convenient, Pythonic way to calculate the length of a WKT linestring according ...
5k views

How do I get the area of a WGS84 polygon in square meters?

The following gives me the area of the polygon in square degrees: SELECT ST_Area(ST_GeomFromText('POLYGON((871325.790874952 6105405.3261047,871418.748307692 6105359.72944624,871346.22022442 6105215....
4k views

Converting Lambert Conformal Conic to WGS84 using Proj.4

I am attempting to transform data from Lambert Conformal Conic lat/long and I am having some issues with the results. The shapefile I am attemtping to transform can be found here: http://tfr.faa.gov/...
12k views

How to calculate new point coordinates from distance and angle using ArcGIS SDK for iOS?

I want to calculate the coordinates of a new point. What I have: The source point coordinates, the distance (meters) and the angle For example: I want to create a point within 100 meters and 45 ...
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 ...
2k views

Converting Ordnance Survey raster maps to WGS84 webmap tiles

I would like to generate Google/Bing-like map tiles from Ordnance Survey's 1:25000 and 1:50000 raster maps, which are provided as 4000x4000 UK national grid tiles (GeoTIFF). A sample tile can be ...
1k views

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(...
672 views

How do I convert Eastings and Northings projection to WSG84 in geopandas?

I'm very new to projections and struggling to convert a map dataset from OSGB36 (Eastings and Northings) to WGS84 (lat/longs). I've used geopandas to import a shapefile. Now I want to export it as ...
1k views

Proper gdaltransform syntax to transform a list of coordinates?

this is probably a very simple question, but I'm very new to GIS so I just need one last nudge. I've got a sense of the Linux utility gdaltransform and I am feeding it coordinate pairs in line-by-...
3k views

How to reproject MODIS Swath data to WGS84

Im new to GIS and now working with MODIS04L2 Aerosol Optical Thickness image. I need to reproject the image to other coordinate system such as WGS84 for later work but now Im stuck with it. I have try ...
150 views

Rhombus shaped pixels when viewing an image referenced in WGS84

Following the Question What is the projection of WGS84 in GIS software?, in the comments section of the answer http://gis.stackexchange.com/a/73578/5256, Jake very well explains that Because the ...
3k views

How to convert (geodetic pose + cartesian offset) to geodetic position

I am in search of an algorithm to solve the first/direct geodetic problem precisely in 3D. The input is: a geodetic (not geocentric) position (WGS84, height is above the WGS84 reference ellipsoid) ...
5k views

Code to convert WGS84 coordinates to British National Grid Easting/Northings

I'm looking for some code, ideally C#, to convert a WGS84 coordinate to British National Grid Easting and Northings. Does anyone have this to hand? I tried converting the Javascript code here: http:...
4k views

How to convert projection

I got sample shape files with the following *prj file content: *PROJCS["RGF93_Lambert_93",GEOGCS["GCS_RGF_1993",DATUM["D_RGF_1993",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",...
147 views

Polygons across international dateline [-180..+180 longitude]

I'm trying to generate polygons for satellite orbital swaths. So far I have a method to generate two lines which represent the edge of each swath in [lat,long]. Some of the swath's cross the ...
8k views

How to recalc WGS84 Shape_Area field to square miles in ArcGIS 10

What are the units of the Shape_Area field in a wgs84 feature class? Is it decimal degree squared? I would like to convert that to something more meaningful like square miles without reprojecting the ...
2k views

Merge geojson polygons with WGS84 coordinate

I have a Geojson file with some adjacent polygons and I want to merge them into one. I know it's a recurrent question but I can't find information for polygons with latitude and longitude coordinates ...
26 views

Given WGS84 bounding box, is there service that returns most accurate projection to use?

I'd like to find a service to convert lat/lon in WGS84 to an arbitrary coordinate system in metric that will be the most accurate for my bounding box. Does something like this exist? For instance, ...
1k views

Finding projection of point to line?

I have a segment defined by 2 LatLon points(A and B) and a third LatLon point (C). I need an alghorithm, formulae, or some code to find the projection point of C on the segment AB (call this point D) ...
5k views

Searching for c# code to convert from UTM to WGS1984 (and back)

I'm looking for code in c# that converts coordinates from UTM to WGS1984 (and preferably backwards as well). I need to convert coordinates from only one zone (36N). I've found this and this, but they ...
259 views

Mis-aligned shapefiles in QGIS?

I'm a beginner at QGIS and I'm having trouble aligning my shapefiles. I have two datasets: one originally in WGS84 (lat/long) and another in Corrego Alegre/UTM zone 24S. I need to convert the second ...
3k views

Transform from WGS84 to EPSG 3785 (google maps)

I am a Java Developer and I was given this coordinates from a database verbat_sistema_coordenadas verbatim_SRS datum verbat_longitud verbat_latitud UTM WGS84 ...
339 views

What is the altitude difference between WGS84 and NAD27 Zone II?

I have a point cloud in a piece of software and have exported the point in both WGS84 and NAD27 State Plane California Zone II (in US survey feet). The WGS data looks like this, with elevation in ...
633 views

On the fly transformation From WGS84 to NAD27 with proj4 code

I want to use this proj4 code: +proj=utm +zone=19 +ellps=WGS84 +toclrk66=-3,142,183,0,0,0,0 +units=m +no_defs or this one +proj=utm +zone=19 +ellps=WGS84 +tonad27=-3,142,183,0,0,0,0 +units=m +no_defs ...
5k views

Converting from British National Grid (27700) to WGS84 (4326) to Web Mercator (102100)

I'm developing a web application that uses ArcGIS to display a map using JavaScript. We are holding all our data in MS SQL Server 2008 as Easting/Northing against the British National Grid. ...
1k views

How do you convert SRTM HGT elevations from WGS84 into meters above sea level?

I am building a JavaScript script that reads binary HGT files - as generated by the SRTM - and converts the data into bitmaps viewable in your browser. You can try out the script and view the source ...
6k views

Convert Lambert Conformal Conic to WGS84

I am trying to convert my "Lambert Conformal Conic map with 2 standard parallels" to the basic/standard WGS84 projection that Google Maps use. I have 30 of these maps which I need to convert. They ...
327 views

Scalebar gives error in measurement in Qgis: Different measurements of distance on OSM tiles and GoogleEarth

I've created a map of Bordeaux using the QGIS map compositor by following this procedure: Used the OSM plugin to display an OSM map and zoomed to Bordeaux Used the print composer to create a map of ...
2k views

Transform Shapefile from WGS84 to NAD83 using QGIS? [duplicate]

Possible Duplicate: How to reproject a vector layer in QGIS? I have some shapefiles whose CRS is WGS 1984 and I have some shapefiles whose CRS is NAD 1983 State Plane Illinois East. I want ...
811 views

Converting Lat/Lon to Pixel-XY on cropped map?

I have a GPX-Track containing LatLon coordinates based on WGS84. The track should be drawn on a cropped map, and for this, I need the pixel coordinates. The map tiles are from OSM I'm not quite sure ...