A map projection is any method of representing the surface of a sphere or other three-dimensional body on a plane
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Real-world example of Affine Transform?
From the Wikipedia article:
In geometry, an affine transformation or affine map or an affinity (from the Latin, affinis, "connected with") between two vector spaces (strictly speaking, two affine ...
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What is the right solution (and map projection) to compute distances between points located all over the World?
After my study on map projection I realized that it is very difficult to choose a projection that allows to compute simultaneously the distances between a great deal of points if these points are ...
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629 views
What kinds of line segments/edges require high accuracy in a true surface-of-the-ellipsoid representation?
I've been musing (and doing prototype coding) for a 'projection free' geographic codebase with your basic point, line & polygon primitives.
Rather than dealing with all the sacrifices that come ...
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1answer
179 views
Great-circle lines in Equirectangular projection
Just to check that I'm on the right track:
Are all great-circles on the sphere and in equirectangular projection (i.e. latitude, longitude pairs) either:
meridians (i.e. going pole to pole)
of the ...
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1answer
659 views
What is the standard Mercator projection?
I'm using QGIS in order to re-project a shapefile I have into "Mercator" so that something like protoviz understands my co-ordinates. Protoviz tells me "Mercator" ...
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1answer
228 views
An example Tissot ellipse for an Equirectangular Projection?
I am trying to calculate distortion of an equirectangular projection via Tissot indicatrices. I have tried following the directions on this post (among other things) but it is beyond my understanding ...
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What happens to a feature class when importing to a feature dataset?
I am creating a model that needs to ensure that all input datasets end up in the same coordinate system (among other things). I was originally going to batch project all of the datasets whether they ...
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2answers
236 views
how to produce a Peirce quincuncial map?
As far as I know neither PROJ4 nor ESRI tools can apply the Peirce quincuncial projection.
Does anybody know what libraries/softwares can manage it?
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1answer
551 views
QGIS- “On the fly” projection ON by default?
In QGIS 1.6, can users set "on the fly projection" to be checked ON by default (at application launch)? I know how to turn it on, but some users find they use it more often than not, and would like ...
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5answers
2k views
Better Distance Measurements in Web Mercator Projection
I am working with an ESRI stack, storing my layers in a sql-spatial-enabled-SDE- geodatabase (Geometry type, Web Mercator-3857).
I am building a web mapping application, so by default, the tiles are ...
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2answers
2k views
EPSG 3857 or 4326 for GoogleMaps, OpenStreetMap and Leaflet
The discussion at What is the difference between WGS84 and EPSG4326? shows that 4326 is just the EPSG identifier of WGS84..
Wikipedia entries for Google Maps and OpenStreetMap shows that they both ...
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Is the quadrilateralized spherical cube map projection the same as Snyder's cubic equal area map projection?
Is the quadrilateralized spherical cube map projection [1] the same as Snyder's cubic equal area map projection [2]?
I know both are equal area polyhedral map projections ( ...
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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 ...
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2answers
271 views
Why are there both square and rectangle world maps?
When i search for images of earth divides to longitude ans latitudes seems that the are 2 major types:
is a perfect square and the latitudes in it are grow a different rate from the equator to up ...
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3answers
396 views
Method to generate points in any projection
I am writing an application in ArcMap to generate a grid of points. These points have a very defined layout and I have worked out an algorithm that works great under a projected coordinate system. ...
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2answers
268 views
How to determine projection parameters when customizing a projection
I am trying to customize an Albers and a Hotine Oblique Mercator (HOM) projection to minimuze distortion in the region I am analyzing. The region extends from about 51 to 62 degrees latitude, covering ...
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5answers
881 views
Calculate distance in km to nearest points (given in lat/long) using ArcGIS
I have two point datasets in ArcGIS, both of which are given in WGS84 lat/lon co-ordinates and the points are spread across the whole world. I would like to find the nearest point in Dataset A to each ...
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2answers
598 views
Bertin 1953 map projection settings
I am trying to use the Bertin 1953 map projection, as described in the book "Semiology of graphics" by Jacques Bertin. But I can't find the settings in any of my GIS software.
Does anybody have a ...
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2answers
426 views
How do I rotate the OSM map before printing?
What is the simplest way to rotate and render Openstreetmap data, and still get a nice render? For example Toronto, would fit best rotated slightly on a page in landscape mode, so the northern ...
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1answer
95 views
Which training courses in Geodetics can you recommend?
Can anyone recommend any training courses in geodesy which would cover the following objectives:
Case studies on coordinate issues
Overview of geodetic datums, coordinate reference systems and ...
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2answers
235 views
What projection does the global climate region map from Wikipedia use?
I would like to use this global climate region map from Wikipedia as a "basemap" (by plotting over the image in R).
Is it possible to determine the projection of this map?
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5answers
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OpenLayers: ALL image layers are out of place on google maps v3 and OSM base layers
Summary:
I have 2 different image layers that looked fine with my old mapstraction/google maps based system. Using the same coordinates as bounds in openlayers results in a shift to the north by like ...
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2answers
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Is it possible to reproject spatial data using SQL Server?
SQL Server takes an SRID when creating spatial data, but is it possible to retrieve an object as a different spheroid?
For example, let's say I have a bunch of spatial polygons using SRID 4258, but ...
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2answers
2k views
Derive WGS84 Longitude & Latitude from British Northings & Eastings
I'm looking for a fairly simple way to append columns with WGS84 longitude and latitude to a table containing northings and eastings. The source data is Ordnance Survey's CodePoint Open, which I is ...
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2answers
98 views
IDW spatial interpolation: appropriate projection?
I am wondering if anyone can clarify whether point data should be projected to an equidistant projection when using ArcGIS IDW spatial interpolation?
I am working on a dataset from Western North ...
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1answer
4k views
How can I transform GCS_North_American_1983 to GCS_WGS_1984?
I posted a thread today describing a shift in some of the NRC data (not all). Apparently, this shift has to do with conversion between Geographic coordinates, latitude and longitude and Transverse ...
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1answer
175 views
Create Mercator map with arbitrary center/orientation?
I want to see a Mercator map where I choose what latitude/longitude is
in the center and what direction is "north". In some sense, a Mercator
map of a rigid rotation of the globe.
Does such a ...
6
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2answers
696 views
ArcGIS 10 British National Grid Transformation
In ArcGIS 10 a new transformation has been added for converting between WGS84 and British National Grid. What is OSGB_1936_To_WGS_1984_NGA_7PAR? How should it be used when compared with the other ...
6
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1answer
626 views
Python script to convert Lat Long to ITM (Irish Transverse Mercator)
I am currently working on a python script that converts Lat Long (WGS84) to ITM. The formulas used are based on a paper published by OSGB (Appendix B):
...
6
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1answer
359 views
SRID error in mapserver
I've created a network topology using QGIS, saved it as a shp, imported it into PostGIS using shp2pgsql and I'm now trying to output some of the geometry using mapserver.
Unfortunately mapserver is ...
6
votes
1answer
77 views
Is there a name for map projections that produce two disks?
I've seen lots of world maps in the shape of two disks that touch, each one a separate projection of one hemisphere onto a disk -- usually the Western Hemisphere and the Eastern Hemisphere -- so ...
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1answer
153 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 ...
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1answer
110 views
Is there a difference between projecting shapefiles then rasterizing & rasterizing shapefiles then projecting?
I currently have a project where I rasterize shapefiles into simple presence/absence (1 & 0) rasters and then add each one to a running total to create a total richness raster at the end. The ...
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1answer
82 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 ...
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1answer
561 views
Which is the correct projection in ArcGIS for EPSG:3857/900913?
I want to publish a mapservice in ArcGIS server, which will be overlayed on Google Maps or Bing Maps. For this, the Map Service needs to be in EPSG:3857/900913.
The Google Maps projection is supposed ...
6
votes
1answer
154 views
What's a robust strategy for displaying 3D map data for navigation?
3D map data, specifically the kind you see on GPS units, or more recently on smart phones, almost always features a 'HUD' like view, which I'm trying to implement in an application of mine. I have ...
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6answers
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Southern hemisphere projections for Landsat upsets GRASS
Hi All
does anyone have the last word on why Landsat scenes don't project in the southern hemisphere. This causes no end of trouble in GRASS, less so in QGIS.
What I mean is, take an original scene ...
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3answers
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Why don't my Shapefiles and OSM data overlap in Quantum GIS?
So I'm pretty new to GIS, and I'm working on a mapping project using data for Vancouver, Canada. I want to combine Open Street Map data along with data provided by the City of Vancouver. But the City ...
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2answers
241 views
Mass-update the projection in compressed GeoTIFF files
I have a huge set of compressed GeoTIFF files. Someone forgot to set the projection while creating the GeoTIFF files and I would like to add it now.
If I use
gdalwarp -t_srs source.tif ...
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2answers
231 views
Arcmap: Create a projection to emphasize a given direction?
Suppose one had a dataset (centered on a given coordinate) of lines that were very close together in terms of longitude but also had important turns/bends far separated by latitude. In order to map ...
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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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1answer
927 views
Mercator projection: problem with latitude formula
I'm trying to get the position of a coordinate on this map (source Wikipedia):
If I'm correct than the formula for the position of the latitude would be:
R * ln(tan(pi/4 + latitude / 2))
But ...
5
votes
1answer
271 views
How does OpenLayers determine a layer's projection?
Could anyone explain the strategy OpenLayers take to determine the layer's projection?
For example, if I didn't explicitly specify any projection for a marker layer, what projection would the layer ...
5
votes
1answer
266 views
Which projection casts rays from a point on the surface of the globe to a cylinder?
What is the name of a map projection that casts rays from a point on the surface of the globe to a cylinder?
Some people who make sundials put a map of Earth on the sundial.
I want to use the "right" ...
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votes
2answers
228 views
Does the Chamberlin trimetric projection map (some) great circles to straight lines?
I know that, in general, the Chamberlin trimetric projection maps most great circles on the sphere to some sort of non-straight curve on the flat map.
But what about the 3 special great circles ...
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1answer
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Projections appropriate for global analysis that preserve area and that preserve distance (but not necessarily in the same projection)
I am looking for a projection (or a set of projections) that decently preserve distances so that I can buffer every country in the world and have a similar level of minimal distortion for each.
I ...
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1answer
65 views
Having trouble finding out what coordinate system a map is using, and how to convert it
I'm using Small Area shapefiles in Ireland from the Central Statistics Office (CSO) website. The link to these is here http://census.cso.ie/censusasp/saps/boundaries/ED_SA%20Disclaimer1.htm (Look for ...
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1answer
346 views
Custom Geographic Transformation on QGIS
Is there a way to create a custom geographic transformation with specifics parameters in QGIS like in ArcGIS?
Okay, I want to tranform SAD69 system into WGS84. Well, I'm in doubt because in ArcGIS ...
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1answer
154 views
What is the definition for a geographic coordinate system with east/west bounds of 0 to 360
I need the coordinate system reference or a projection definition that uses geographic (i.e. lat/lon) coordinates but instead of east/west bounds being defined as 180 to -180, I need them to be ...
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3answers
674 views
Plot a EPSG:4326 KML File using Google Maps V3
I have a KML file that uses EPSG:4326.
Is there any way to plot this onto a Google Map (v3) which uses Mercator?
Here is the page I am working on
The district data comes from one source and is ...
