Tagged Questions

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

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3
votes
1answer
1k 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 ...
8
votes
1answer
2k 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 ...
1
vote
2answers
2k views

What do I need to change to get scale bar units other than degrees?

Measurements done in QGIS on my project are done properly using whatever unit is set in: Settings > Options > Map Tools > Preferred measurements units but the scale bar decoration and scale bar in ...
1
vote
1answer
2k views

How to Project shapefile from NAD 1983 UTM Zone 12 to WGS 1984 UTM Zone 13N?

I have a question and I have a shapefile that is in NAD UTM Zone 12 and Datum is North American Datum of 1983. What I would liket to reprojection it to NAD 1983 UTM Zone 13N and change the Datum to ...
1
vote
0answers
384 views

Possible to do a datum shift using dotSpatial?

I was hoping to be able to use Reproject.ReprojectPoints to achieve a datum shift between lat/lon values in NAD27 and NAD83. I'm able to correctly reproject from NAD27 lat/lon to NAD27 UTM and from ...
2
votes
3answers
386 views

Datum transformations, do we use wgs84 as an intermediate common reference?

I was transforming some data the other day using the 7 param helmert transformation and it got me thinking. I have a set of transformation parameters, but these only describe the transformation from ...
11
votes
3answers
330 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 ...
0
votes
0answers
108 views

How to determine Earth co-ordinates?

I just read about latitudes and longitudes. I read latitudes are imaginary lines that run around the earth and longitudes are lines that run around from top to bottom. Using this system: 1. ...
1
vote
1answer
136 views

Tool For Generating Formula for Projection

I am using Proj4Js for northing,easting to lat,long transformation. My Datum is "AGD84" and projection is "Transverse Mercator". While doing so I found that if I don't specify "+proj" parameter in ...
27
votes
2answers
2k 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 ...
1
vote
0answers
343 views

Conversion From Transverse Mercator To Longitude & Lattitude

I have to transform (7-parameters datum transformation) coordinates from northings & eastings to lattitude & longitude. Following are details of source coordinate system(i.e. northings & ...
20
votes
1answer
4k 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 ...
3
votes
1answer
1k 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 ...
8
votes
1answer
3k 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 ...
1
vote
2answers
3k views

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

I'm developing a web application that uses ESRI 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. ...
1
vote
1answer
369 views

What datum (reference ellipsoid) does Nasa Worldwind use?

What datum (reference ellipsoid) does Nasa Worldwind use? I can't seem to find where Nasa Worldwind tells explicitly what datum they use. I need some sort of valid link.
7
votes
2answers
4k 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 ...
2
votes
3answers
130 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 ...
4
votes
2answers
590 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 ...
2
votes
3answers
2k views

What Geotransformation (NAD27 to WGS84) should I use for Gulf of Mexico?

I'm working with datasets that are spread out across the northern part of the Gulf of Mexico, stored in NAD 27. I've been told the polygons shown above were obtained from BOEMRE (formerly known as ...
3
votes
1answer
313 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: ...
3
votes
3answers
776 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 ...
12
votes
1answer
510 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 ...
4
votes
1answer
980 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 ...
5
votes
2answers
5k 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 ...
8
votes
1answer
618 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 ...
3
votes
1answer
599 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?
5
votes
2answers
3k 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 ...
44
votes
7answers
3k views

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 ...
5
votes
2answers
600 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 ...
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: ...
5
votes
3answers
277 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 ...
129
votes
12answers
31k views