The information connecting numerical coordinates to actual locations on the earth.

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163
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11answers
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48
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7answers
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What strategies, criteria, or rules to use for selecting coordinate systems?

What strategies, criteria, or rules do you use for selecting coordinate systems for (a) storing, (b) analyzing, and (c) displaying GIS data? (I humbly offer my reply to a related question ...
31
votes
2answers
4k views

How accurate is approximating the Earth as a sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
25
votes
1answer
9k views

Is WGS84 itself a Coordinate Reference System?

I was wondering the difference between WGS84 and EPSG:4326 (see this). Can then WGS84 on its own be defined as a Coordinate Reference System? Or is it just a datum so that a Coordinate System must ...
12
votes
1answer
628 views

How is a “conformal latitude” used in ellipsoidal stereographic projections?

At my work, I've been doing some maintenance on internal software that claims to implement a Stereographic projection whose formulas were copied from an old system a long time ago. From what I've ...
11
votes
1answer
687 views

why does the North American Datum not actually include north america in it's boundary?

http://spatialreference.org/ref/epsg/4269/ That link shows the area that the North American Datum 1983 covers and one thing I note is that it doesn't cover North America. It covers all of Asia and ...
11
votes
3answers
374 views

Does Earth's magnetic field affect any datum definition?

I had an interview last week. One very interesting question was "does earth's magnetic field affect any datum definition?" I was sure it does not for geocentric datums. But I thought maybe the ...
11
votes
2answers
729 views

Huge differences between results for 7-param datum transform

I'm trying to transform a WGS84 lat/lon point 11d42'32.10629" E 5d12'56.75371" S in three different software packages (Proj4, GeoTrans and Leica GeoOffice) but I receive very big differences ...
10
votes
3answers
663 views

What is the meaning of “Elevation above the surface of the 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 ...
9
votes
1answer
5k views

How to reproject a raster file in QGIS with datum transformation?

I want to reproject a tiff raster file from projection A (ETRS89/UTM Zone 32) to projection B (DHDN/Gauss-Kruger zone 2). The two projections have a different datum so I have to use a datum ...
9
votes
1answer
6k 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 ...
9
votes
2answers
414 views

How do I perform a 3 parameter geotransformation and projection in Sql Server 2012?

I have a table with latitude longitude (NAD27) columns in it. I compute two other columns, X and Y, representing Web Mercator (WGS84) location. Currently I'm using a Arcmap to do this, by applying ...
8
votes
3answers
8k 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 ...
8
votes
1answer
748 views

WGS72 to NAD83- how to find correct transformation

I am trying to get this raster file to convert from WGS72 to NAD83, but ArcMap10 doesn't appear to have the correct transformation listed. Where can I find this transformation, and/or how do I import ...
7
votes
2answers
286 views

Geo-referencing an old map

I'm trying to georeference this part of an old map of Indochina. . The full extent gives more information: . To do so, I used QGIS and tried to infere the datum, I tried "Unknown datum based on ...
6
votes
3answers
111 views

Vertical datum query for coastal modeling

This may be very specific. I have a USGS derived DEM with a vertical datum of EGM96 from NASA satellite data. My Bathymetry uses a lowest astronomical tide datum. Has anybody come across this or ...
6
votes
1answer
2k views

Determine the UTM zone/hemisphere in a particular datum

I'm using GDAL to convert coordinates from one system (geographic or projected) to another. Assume I want to convert geographic coordinates (latitude and longitude) in the WGS84 datum, to UTM ...
6
votes
2answers
7k views

Basic proj4 conversion UTM grid -> longlat and back

I'm a GIS novice, and am struggling to understand how to drive proj4 to accomplish what seems like a simple thing. I've googled for a couple of days, but everything I find seems to presuppose quite ...
5
votes
2answers
2k views

How to convert from one ellipsoid to another?

Introduction I have the following problem: I want to convert from WGS84 to "Anguilla 1957 / British West Indies Grid" (EPSG 2000). This seems to be straight-forward, as the transformation is a simple ...
5
votes
2answers
4k views

How do I use GDAL to convert from an arbitrary projection/datum into Equirectangular/WGS84?

I've been trying to use GDAL to convert from an arbitrary projection/datum into Equirectangular (aka Plate Caree, aka Equidistant Cylindrical, aka Geographic, aka Lat/Long) with WGS84 datum. All of ...
5
votes
1answer
116 views

Is there a way to determine the datum used when all you have is a lon and lat?

I have a dataset of US intersections from 2011 that I'm going to be using in a project together with data based in WGS84. Included in the CSV file is a variety of fields two of which are the lat and ...
5
votes
2answers
743 views

Why are the coordinates transformed with proj.4 off compared to http://valdemar.kms.dk/trf/?

I am trying to transform from epsg:4326 (wgs84) to epsg:25832 (utm ETRS89) using Proj.4. I am comparing the results with results from http://valdemar.kms.dk/trf/ . it seems like the results ...
5
votes
3answers
315 views

How to manually change from GPS (WGS84) to web based maps projection systems?

I have collected location point data and wish to display this on a web based map. It was collected using a Garmin Etrex GPS using the WGS84 datum. I wish to display the points using Ushahidi and have ...
4
votes
2answers
111 views

Are Australian Height Datum and GDA94 applicable to Christmas, Lord Howe, and Norfolk islands?

I've been asked to recommend a mapping coordinate reference frame for use for Australian mapping, which I've said AHD for the vertical component and GDA94 for the the horizontal component. However, ...
4
votes
2answers
898 views

Geographic Transformations in Alaska Between NAD83 and WGS84

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 ...
4
votes
3answers
1k views

Vertical Datum Conversion Utilities

I have some data (points and rasters) that I would like to be able to convert to and from several vertical datums, including MLLW in coastal Florida. I would appreciate it if people could provide some ...
4
votes
3answers
3k views

Parameters for ED50 -> ETRS89/WGS84 seven-parameter transformation which are good for Denmark?

I am looking for parameters for a seven-parameter transformation (Rx, Ry, Rz, Tx, Ty, Tz, s) from ED50 UTM (zone 32U) to ETRS89 and/or WGS84. The best match I could find is here: ...
4
votes
1answer
420 views

Canadian Geodetic Vertical Datum of 2013 (CGVD2013)

"Natural Resources Canada (NRCan) has released the Canadian Geodetic Vertical Datum of 2013 (CGVD2013), which is now the new reference standard for heights across Canada. This new height reference ...
4
votes
2answers
141 views

towgs Definition for European Datum 1950

I am new to all things GIS so apologies for a basic questions. I am trying to specify the CRS of a climatic raster layer in R. It is an equal area projection based on Europe Equidistant Conic and the ...
4
votes
1answer
296 views

Error in Min. Bounding Geometry results

I'm getting consistent, weird results from using Minimum Bounding Geometry to make circle polygons. I'm not sure if a datum issue, but I'm leaning more towards something wrong with Minimum Bounding ...
4
votes
2answers
871 views

Converting Geocentric to Geodetic

I am only looking for a confirmation of what I believe to be true. If my explaination or conclusion is not accurate I would appreciate it if the reason can be explained to me. Background ...
4
votes
1answer
15 views

WRF Spherical Earth to WGS 84

Weather Research Forcasting Model assumes a spherical earth model with a radius of 6370km. I'm looking to display the data onto the WGS-84 Ellipsoid model as that is the model my system uses for its ...
3
votes
2answers
2k views

What is the process to calculate Helmert parameters?

I have some double points (the same points in 2 different datums). I'd like to calculate the Helmert parameters but I don't understand how. NOTE: I don't need software. I need an algorithm in order ...
3
votes
1answer
220 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 ...
3
votes
1answer
102 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 ...
3
votes
2answers
46 views

How to re-project a shapefile to be compatible with another shapefile or raster?

I have a polygon shapefile and a raster. The shapefile and raster have different coordinate systems. Coordinate System for the shapefile: NAD_1983_UTM_Zone_19N WKID: 26919 Authority: EPSG ...
3
votes
4answers
1k 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 ...
3
votes
2answers
452 views

GeometryServer > Project with Datum Transformation

I am facing the problem that when i use the extent in the url and i go from Amersfoort(WKID 4289) to WGS84(WKID 4326) that without the tranformation the point from longitude and latitude is placed ...
3
votes
2answers
2k views

Where is list of Geographic Transformations in ArcGIS, and their areas of applicability?

I have some data in Provisional South American Datum 1956, and I need to project it to Web Mercator with WGS84 as the datum. When I use the project tool in ArcGIS desktop, it requires a Geographic ...
3
votes
1answer
2k views

ArcGIS 10.0/10.1 - arcpy - automate projection tool with different datum or projection

I am getting stuck with a task that is slightly different from the posts I found so far on this same website. Assumption: all layers have a defined coordinate system Problem: I would like to ...
3
votes
1answer
2k views

How to perform datum transformation in ArcGIS server REST API exportmap

I have a ArcGIS server 10.0 mapcontext in one projection (swedish grid sweref99 TM) which uses its own datum, also named Sweref99 . When I use the REST API's map service export function I want to ...
3
votes
1answer
46 views

What does it mean for two datums to be navigationally equivalent?

I read from NOAA that NAD83 and WGS84 are "navigationally equivalent" NOAA uses the North American Datum of 1983 (NAD 83) for all of its charts. This datum is navigationally equivalent to the ...
3
votes
2answers
65 views

What is the closest CRS to “Meridiano de Greenwich”

I have a 1906 scanned map that I am trying to georeference in QGIS for Mac. The map has French and English lat-long, indicating them as either "Meridiano de Greenwich" or "Meridiano de Paris." I would ...
3
votes
1answer
754 views

datum conflict when creating buffer in arcgis 10

A buffer I created successfully executed, but I received the following message: "WARNING 000632: Datum conflict between map and output." How can I fix this?
3
votes
2answers
219 views

methods for converting coordinate datum and format in python?

Related to an earlier Q&A of Missing grid shift files for cs2cs.exe? ... what are the various methods to convert coordinate datum and format in python? (Windows Vista, python 3.4) For example, ...
3
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1answer
169 views

Reprojecting between NAD27 and WGS 84 part III

I am trying to perform a reprojection for data with datum Nad27 to WGS84 datum. According to AndreJ in some previous questions in Stackexchange (CRS reprojection for instance) QGIS uses internally by ...
3
votes
0answers
46 views

Do locations “move” when shifting datum?

I hope that this is the right Stack Exchange for this question. I may be oversimplifying this, but I'm looking for verification in my understanding of the following: If I have a spatial dataset in 2 ...
3
votes
0answers
698 views

How to set GDAL/cs2cs/proj to use NTv2 grid shift file when using EPSG codes?

I am using the GDAL API for Python for a script that takes only EPSG codes for inputs to specify source and target coordinate systems. While the cs2cs command seems to handle quite well ...
3
votes
1answer
383 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: ...
2
votes
3answers
139 views

What Danish position format is this?

I have been given a list of locations within Denmark. Most of the are in decimal degrees. However, some of the positions are in different formats and I can't figure them out. Does anyone recognize ...