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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5
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318 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 ...
39
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5answers
10k views

Why is the 'straight line' path across continent so curved?

This is the result of mapping the straight line path from a point in US to Poland using Distance Measurement Tool. Also, planes from Asia to US would travel almost over North Pole. Why is the path ...
4
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1answer
261 views

Using projections to obtain perspective views

I understand that a perspective view is essentially a type of projection. Is it possible to create projection definitions for a typical GIS system that will mimic a perspective view from a particular ...
2
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2answers
914 views

albers projection to Lat, Lon

Thanks in advance for helping me with my issue. This GIS stuff is using parts of my brain that have remained idle since high school, and some parts are working faster than others. I have land data ...
5
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1answer
3k 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: ...
4
votes
1answer
528 views

How can I specify a PROJ.4 projection with the north pointing *down*?

I would like to create a world map "upside down", with the south on top (in Mapnik). Can I take an existing projection string, e.g. Robinson projection +proj=robin +lon_0=0 +x_0=0 +y_0=0 ...
8
votes
1answer
706 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 ...
3
votes
1answer
2k views

OpenLayers doesn't show an overlay with a different SRS than the base layer

I need to add an overlay layer that uses EPSG:4326 to a map with a base layer that uses EPSG:32628. Every time I add the overlay OpenLayers automatically switches the SRS param of the overlay to ...
8
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3answers
804 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 ...
6
votes
2answers
6k 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 ...
10
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3answers
2k views

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 ...
1
vote
2answers
601 views

How to add new projection using ArcObjects of ArcGIS for Desktop?

I want to use "Mars MOLA" { 86 3396000.0 3396000.0 "Mars MOLA" 0 0 0 0 0 0 0 } with my shapefiles.
2
votes
2answers
1k views

Converting google map api coordinates into meters

How would I go about converting the results of my map bounding box into meters within javascript? For example, if I have the coordinates 51.52366625446907, -0.07467269897460938 decimal degrees, can I ...
8
votes
2answers
712 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 ...
4
votes
1answer
452 views

No difference between distances measured in projected and non-projected data

I'm performing measurements of distances in Km between a lot of localities by using the "Point Distance" in ArcGis 9.3. I realized that the results obtained after using projected coordinate system are ...
22
votes
1answer
2k views

How to create an accurate Tissot Indicatrix?

A Tissot Indicatrix is useful method for communicating at a glance the kinds of distortion a given projection is prone to (in the figure below, each of the red circles occupies the same area). I've ...
20
votes
6answers
15k views

Defining projections for multiple shapefiles in ArcMap?

I have over 100 shape files that don't have .prj file and thus when I bring them into ArcMap 10 they show the coordinate system as unknown. I know all of the shape files coordinate system is GCS WGS ...
9
votes
4answers
742 views

World map projection with United States in center

I am creating a map showing flight paths originating in the United States and traveling to Asia and Europe. I need a projection for the world that will focus the United States in the center of the ...
2
votes
1answer
1k views

Conversion of any projection to latlong using proj4 string

I am using a tool which uses proj4 lib to project maps. I have a set of xy coordinates to be converted to latlongs with that tool. as I have the source projection string say +proj=aea +datum=NAD83 ...
8
votes
6answers
1k views

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 ...
4
votes
2answers
1k views

Projected maps don't overlap

I am very new to arcGIS and so apologise if this is a really simple question, but it has had me (and what I can find on the internet beat for 2 days now. I am trying to build a series of layers of ...
6
votes
1answer
9k 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 ...
3
votes
3answers
383 views

Is there a projection issue with the NRC Canada Atlas hydrology data?

I have been using the Natural Resources Canada (NRC) data for various generalized maps but it is not until now when i overlaid higher resolution features obtained from the provincial government ...
6
votes
2answers
1k 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 ...
5
votes
3answers
855 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 ...
4
votes
3answers
229 views

Does a projection's WKT reflect the computer's locale?

This should be quick - we're trying to determine if there are problems parsing some WKT text because the system locale considers the decimal separator to be a comma instead of a period. Anyone know? ...
9
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2answers
3k 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 ...
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 ...
2
votes
1answer
653 views

I have several layers (polylines and polygons) that are of the same area but they don't overlap in ArcMap as they should, what do I do?

For my GIS project for my class, I have downloaded several vector layers from different websites (polyline of the continental divide, a boundary polygon of New Mexico, a rivers and water bodies layer ...
4
votes
4answers
7k views

Correcting a table's projection in MapInfo

Occasionally I have a MapInfo TAB file that doesn't match up with others. Presumably this is because MapInfo is interpreting it as a different projection to the one it was saved as. I am also assuming ...
7
votes
3answers
463 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. ...
11
votes
7answers
396 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 ...
6
votes
1answer
466 views

Equal Area SRID for Australia

This has been bothering me for some time so I figured I would put it out there. Does anyone know the SRID for an equal area projection that is suitable for the whole of Australia? I realize that I ...
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 ...
11
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3answers
3k 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?
7
votes
2answers
4k views

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 ...
4
votes
1answer
403 views

what are the main advantages of using a Double Stereo projection?

I'm not per say a GIS guru, I'm more of a user of the technology. On a recent project we were asked to analyze, provide, and submit all our analysis using a Double Stereo projection. What are the main ...
21
votes
3answers
2k 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 ...
5
votes
2answers
653 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 ...
30
votes
2answers
1k views

What coordinate system should be used to store geography data for celestial coordinates?

I am doing an astronomy project. I want to have the information about our images stored in a spatially enabled database. This, I would think, should be a very easy special case for GIS functions ...
14
votes
5answers
2k views

Does Re-Projecting ShapeFile only update content of *.prj file?

if i wish to change the projection of some shapefiles from .. lets say NAD83 (4269) to WGS84 (4326) ... and by using some 3rd party app .... does this mean the .prj file is only updated .. and not the ...
4
votes
1answer
302 views

Is a WMS map always a constant scale?

If I get a map back from a WMS server is the scale always constant over them map regardless of the reference system? So if I have a map which is 100 pixels wide, will the point at 50 pixels always ...
3
votes
2answers
941 views

Which ESRI defined geographic transformation do I need to use to convert my “ NAD83 Northern Virginia” data into WGS 1984 Web Mercator?

My title pretty much tells it all.. I have a number of datasets in which I want to batch project from NAD83 Northern Virginia Datum into the correct Web Mercator projection.. When I do a straight ...
11
votes
6answers
638 views

Where can I find GIS data to test GIS coordinate operations?

I am trying to find some data that can be used to test GIS coordinate operations from one CRS to another CRS. So far all I have found is the Gold Data set and also various example points in the EPSG ...
5
votes
1answer
672 views

What is north-up projection?

How do I know what projection to use for north-up or 0 rotation? I have a gtiff (ND83-nf) that gives me the error when importing to Grass. Should I re-project or recreate the image with the rotation ...
2
votes
1answer
2k views

How can I convert from EUREF-FIN coords to Lat/Long?

See question title, how can I Translate EUREF-FIN coords to Lat Long?
2
votes
3answers
3k views

How to change default projection in ArcPad 10?

Is there a way to set a default projection in ArcPad 10? The only way I can tell is by creating a quickProject based on a project that contains a shapefile with the same projection, but that's just ...
19
votes
10answers
3k views

Discontinuous or Interrupted map projections?

Do any of the current open source GIS softwares support discontinous projection systems? E.g. sinusoidal, dymaxion, butterfly, etc? If not, are there any affordable commercial ones that do (affordable ...
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: ...
3
votes
2answers
339 views

How does ESRI, and how should anyone, transform a coordinate that lies outside a grid transform (e.g. NADCON)?

As I understand it, a datum transform (e.g. urn:ogc:def:coordinateOperation:EPSG::1241) based on a grid interpolation method, e.g. NADCON, is undefined outside of the grid of points. Therefore the ...