A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions.
35
votes
7answers
2k 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 ...
29
votes
3answers
4k views
LatLon or LonLat, what's the “right” way to display coordinates and inputs?
I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it?
I think almost everyone pronounces it as "LatLon". Who ...
21
votes
3answers
11k views
Algorithm for offsetting a latitude/longitude by some amount of meters
I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...
19
votes
3answers
1k views
What was the rationale for the non-standard UTM zones near Norway?
UTM zones 30V, 31V, 32V, 31X, 33X, 35X, and 37X do not line up with the rest of the UTM zone grid.
Why was this allowed? According to Wikipedia, UTM was developed by the U.S. Army Corps of ...
18
votes
8answers
4k views
Best practices for identifying the unknown coordinate system of a Shapefile
I got a Shapefile but it's coordinate system is unknown and there is no .prj file.
How I can identify it now? Are there any tools that could help?
18
votes
3answers
9k views
What is the difference between WGS84 and EPSG4326?
What is the difference between WGS 84 and EPSG 4326? It seems like for a given dataset it might be both WGS 84 and EPSG 4326.
17
votes
7answers
513 views
Spatial reference for dummies?
Can anyone recommend a good reference or tutorial that explains the principles of spatial references, projections, and coordinate systems? We are a small team of programmers working with GIS ...
17
votes
1answer
2k 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 ...
15
votes
6answers
9k views
How can I define projections for multiple shape files in ArcMap 10 at once?
I have over 100 shape files that don't have .prj file and thus when I bring them into ArcMap they show the coordinate system as unknown. I know all of the shape files coordinate system is GCS WGS ...
15
votes
5answers
2k views
How do you best deal with data that spreads across UTM Zones?
I have data that spreads across two UTM Zones GDA/MGA94 UTM Zone 55 and 56. I have layers such as a cadastre, roads, pipelines etc where I want to store measurements like lengths and areas in metres ...
14
votes
7answers
4k views
ArcCatalog 10.0 complains that spatial references don't match between a feature dataset and a feature class that have the same coordinate system?
I have a feature dataset that is using the GCS_WGS_1984 as the geographic coordinate system. It includes a few feature classes.
This feature dataset is itself in a file geodatabase that contains a ...
11
votes
7answers
303 views
Public reprojection services
Are there any free public services where I can send one point in a coordsystem and it returns the point reprojected in a specified coordinate system?
I will not be doing many requests, for now it is ...
11
votes
5answers
9k views
Get list of coordinates for points in a layer?
I've got a layer in QGIS that is comprised of points. Its attribute table doesn't have the corresponding x y coordinates for each point. Is there a way for me to extract a list of coordinates for ...
11
votes
3answers
996 views
Official term for latitude longitude coordinate system?
May I know what is the correct specific term for latitude longitude coordinate system?
With "Geographic Coordinate", it seems to be a general term for every other system?
10
votes
3answers
894 views
Is the GEO tag for QR codes lat/long or long/lat
I just found out that you can add a geographic component to a QR code.
I also just found you can create one on the Google Chart API using this:
...
10
votes
2answers
1k views
Lon/lat transformation
First I should clarify I don't have previous experience with the field, so I don't know the technical terminology. My question is as follows:
I have two weather datasets:
The first one has the ...
9
votes
9answers
4k views
Batch convert lat longs to UTM?
I've got a .csv file that contains a long list of latitude and longitude points. Is there an efficient way to batch convert the list into a projected UTM coordinate system?
Thanks.
9
votes
0answers
449 views
ArcGIS Length and Area Calculation Scenarios
Trying to get a handle on how length and area are calculated in different scenarios in ArcGIS. I don't know why I can't find a answer on the feature class fields, but I can't find a precise answer, ...
8
votes
7answers
787 views
Looking for a tool to convert DD to DMS
I am looking for either an online tool or one that I can download to convert DD to DMS.
For example, I want to convert from:
41.590833, -93.620833 to 41° 35′ 27″ N, 93° 37′ 15″ W ... Those are the ...
8
votes
3answers
4k views
Coordinate System Transformation in ArcMap
For the Data Frame Properties on a map in ArcMap, what is the difference between selecting a new coordinate system and using a Transformation?
8
votes
3answers
281 views
Global grid, which reference system to use?
I have seen a couple global studies using WGS84 as geographic reference, with the problem that the area of raster cells is not constant. Which reference system would you use for a global analysis in ...
8
votes
1answer
166 views
Reprojection - Learning the ins and outs
I would like to expand my knowledge coordinate systems, projections and reprojecting data, with a view of writing a reprojection engine.
Could you provide me with some resources (books, websites, ...
8
votes
1answer
244 views
How can I see the coordinate transformation parameters in QGIS?
How can I see (and edit if possible) the transformation method and parameters used by QGIS for "on-the-fly" transformation, and then for saving data in another CRS? Like in ArcGIS?
Here is the ...
8
votes
2answers
645 views
How can I convert geomagnetic coordinates to geographic coordinates without doing the math myself?
I have some data which are in geomagnetic coordinates; that is, they are latitude and longitude, but in reference to the magnetic north pole in Canada rather than the geographic north pole. As you ...
8
votes
1answer
964 views
How to compute the bounding box of multiple layers in lat/long?
I am writing an application to performance test all kinds of map services, primarily AGS 9.x, AGS 10, and WMS 1.x.
Part of the application involves generating random bounding boxes for individual ...
7
votes
5answers
1k views
What are the advantages / disadvantages of reporting location in decimal degrees versus degree min sec?
Many scientific articles report site location in units of degree/min/sec, but for analysis in with non-GIS software, it is easier to use decimal degrees. Is there a reason for degrees / min / sec to ...
7
votes
2answers
2k views
Measuring distance in spherical Mercator vs zoned UTM
I've got points in WGS84 lat/long and I'd like to measure "small" (less than say 5km) distances between them.
I can use the haversine formula from http://www.movable-type.co.uk/scripts/latlong.html ...
7
votes
1answer
1k views
getExtent() in OpenLayers returns strange values
I'm trying to get the bounding box of the map area displayed by OpenLayers.
I tried to use map.getExtent() because it should be exactly what I need, but the returned values are "strange":
For ...
7
votes
2answers
98 views
Which SRS to use for global distance queries?
I have a database with a lot of points in WGS84.
Now I am building an cache that performs NN and points in range queries using a KDtree. The point [sic] is that the search radius will be provided in ...
7
votes
1answer
532 views
Computational most efficient way to convert Cartesian to Geodetic Coordinates
As far as I understand the literature there are several ways to convert a set of geoecentric cartesian coordinates to geodetic coordinates
Bowring, 1976
Borkowski, 1989
Lin & Wang, 1995
Toms, ...
7
votes
2answers
479 views
Nearest point on a line ( Spherical / Mercator projection )
I have a line (Ax,Ay - Bx,By) over a mercator projection (google maps) and a random point (Cx,Cy) nearest to that line, i would to know the closest point (transparent blue on the image) over that line ...
7
votes
3answers
528 views
Longitudinal Issues with NetCDF data
I am seeking advice on working with world data sets where the GCS has a positive range (0 degrees to 360 degrees). The data I am working with are NetCDF oceanographic data and have positive coordinate ...
6
votes
4answers
425 views
Where should I start advanced GIS learning
I am relatively familiar with most of the GIS stuff. I develop GIS applications as well with open source offerings. Still I find some lapses in my theoretical knowledge in GIS. What resources can you ...
6
votes
7answers
1k views
How can I digitize a PDF image?
I have an image file in pdf format which includes some drawings (lines, closed areas, and points). I want to digitize it into a shapefile so that I can show it on a Google map. I have a couple of ...
6
votes
3answers
1k views
Geodetic Coordinates And Latitude, Longitude
Would it right to say that geodetic coordinates (phi & lambda) are the same as latitude & longitude?
6
votes
2answers
220 views
Why do my Shapefiles not align correctly?
First: I'll summarize what I understand so far so please confirm or correct me.
When On-the-Fly is selected a layer is re-projected from
that of the layer's CRS to that of the project CRS, IF
...
6
votes
2answers
3k views
How do I convert affine coordinates to lat/lng?
I am extremely new to GIS.
I'm using gdal to read in a landuse/landcover map and I need to pick out the lat/lng of certain land cover types to index into a different dataset which is expressed only ...
6
votes
1answer
129 views
Coordinate system in aerial imagery
I am calculating WGS84 coordinates of points in an aerial image, given the WGS84 coordinates of the center of the image and the ground distance width and height (calculated from altitude and lens ...
6
votes
1answer
602 views
Difference between Geographic-3D and Geocentric CRS
I'll start with the OGP definitions:
Geographic. A coordinate reference system based on a geodetic datum and using an ellipsoidal (including spherical) model of the Earth. This provides an accurate ...
6
votes
1answer
74 views
Should I Reproject Data Which Has Been Captured Incorrectly?
I'm working on a project for a client which is migrating data from an Oracle database to an ESRI Geodatabase. When data for this project was initially captured over 15 years ago, the coordinate ...
5
votes
7answers
970 views
Problem with Swiss coordinate system overlay in WMS
I have administrative boundaries data for communities in Switzerland from SwissTopo. Original data came in shape files with 'Bessel 1841 Hotine Oblique Mercator Azimuth Natural Origin' projection.
...
5
votes
2answers
535 views
What is the SRID of census.gov shapfiles?
I downloaded the county files from:
http://www.census.gov/cgi-bin/geo/shapefiles2011/main
I cannot figure out what SRID to use with them. When I am trying to generate a class file from ./manage.py ...
5
votes
1answer
5k views
QGIS - Change unit of measure from degrees to meters
I am running QGIS 1.7.0 on windows, and I donwloaded a shapefile of census block group boundaries from TIGER. This file appears to be in the WGS 84 coordinate system, and when I open it in QGIS the ...
5
votes
2answers
533 views
Quick way to determine if facing a given lat/lon pair with a heading
I'm looking for a fast way, preferably without trigonometric operations (just multiply, divide, add, sqrt and subtract) to determine if a point is visible. E.g. say I am facing 0 degrees N, I am at ...
5
votes
2answers
405 views
Location of Coordinate Systems folder in ArcGIS 10.1
To make it easier to find and select the 3 or 4 coordinate systems we use most often in ArcGIS 9.x and 10.0 we would copy them to the top of the Coordinate Systems folder, generally located in ...
5
votes
1answer
76 views
Where is the Spatial reference ID stored in SpatiaLite?
I have loaded a shapefile into a SpatiaLite Database using the spatialite-gui. In which table is the Spatial reference ID or EPSG code (of the stored data)stored in SpatiaLite?
5
votes
2answers
259 views
What is the origin of the Degrees, Decimal Minutes format?
In my experience, for most non-GIS folks, the most commonly used and understood coordinate system is good old Latitude and Longitude, displayed as degrees, minutes, and seconds (DDMMSS.ss). In GIS, ...
5
votes
1answer
595 views
MGRS in OpenLayers
I am trying to view the Military Grid Reference System coordinates in Openlayers through the MousePosition control. Is there an easy way to accomplish this just through Javascript? I am looking at the ...
5
votes
2answers
409 views
Identify the latitudinal and longitudinal point directly beneath an object in space
Given the azimuth and altitude / latitude and longitude from the observer to the satellite, how can I accurately find the latitude and longitude of the point of intersection directly under the ...
5
votes
2answers
1k 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 ...
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