I'm not quite sure if I'm phrasing this right. It's just occurred to me that lat/longs are two dimensional coordinates like any other projected coordinate system, so it's presumably possible to create a two dimensional map based on these unprojected coordinates.   It would obviously be centred on the point (0,0) (off the west coast of Africa, on the equator), and the 180 meridian would be exactly on the left and right borders.  Is there a name for this kind of "non-projection"? Presumably there are images of it, but I'm just not sure what to look for.
121624
May I know what is the correct specific term for latitude longitude coordinate system?  With "", it seems to be a general term for every other system?
39146
I learned on ArcGIS, and I'm familiarizing myself with the use of QGIS.  So far I love it, but the process of re-projecting and transforming datums seems less intuitive than in Arc.    I recently geocoded 63 locations, pulled in the csv and transformed into a points shapefile. I then set the projection for that points layer as the same for my block groups multi-polygon (EPSG 102121- NAD_1983_Michigan_GeoRef_Feet_US).    The 2 layers are still misaligned, even if I save each layer with the specified projection and try to reopen in a blank project.  Can anyone help?
118235
I copied the example from geotools, which shows how to transform a shapefile into a different projection. () But when transforming from Gauss Krueger 4 into Pseudo Mercator (3857) the shapes are not at the correct position, they are displaced several meters.  What can I do to fix this?  The sample code contains :   CoordinateReferenceSystem dataCRS = schema.getCoordinateReferenceSystem();             CoordinateReferenceSystem worldCRS = map.getCoordinateReferenceSystem();             boolean lenient = true; // allow for some error due to different datums             MathTransform transform = CRS.findMathTransform(dataCRS, worldCRS, lenient);   ... and then ...  Geometry geometry2 = JTS.transform(geometry, transform);   additional information:  The sample data of the source as the following CRS  PROJCS["PD_83_3_degree_Gauss_Kruger_zone_4",    GEOGCS["GCS_PD/83",      DATUM["D_Potsdam_Datum_83",        SPHEROID["Bessel_1841", 6377397.155, 299.1528128]],      PRIMEM["Greenwich", 0.0],      UNIT["degree", 0.017453292519943295],      AXIS["Longitude", EAST],      AXIS["Latitude", NORTH]],    PROJECTION["Transverse_Mercator"],    PARAMETER["central_meridian", 12.0],    PARAMETER["latitude_of_origin", 0.0],    PARAMETER["scale_factor", 1.0],    PARAMETER["false_easting", 4500000.0],    PARAMETER["false_northing", 0.0],    UNIT["m", 1.0],    AXIS["x", EAST],    AXIS["y", NORTH]]   and the target has the following CRS:  PROJCS["WGS 84 / Pseudo-Mercator",    GEOGCS["WGS 84",      DATUM["World Geodetic System 1984",        SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]],        AUTHORITY["EPSG","6326"]],      PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],      UNIT["degree", 0.017453292519943295],      AXIS["Geodetic latitude", NORTH],      AXIS["Geodetic longitude", EAST],      AUTHORITY["EPSG","4326"]],    PROJECTION["Popular Visualisation Pseudo Mercator"],    PARAMETER["semi_minor", 6378137.0],    PARAMETER["latitude_of_origin", 0.0],    PARAMETER["central_meridian", 0.0],    PARAMETER["scale_factor", 1.0],    PARAMETER["false_easting", 0.0],    PARAMETER["false_northing", 0.0],    UNIT["m", 1.0],    AXIS["Easting", EAST],    AXIS["Northing", NORTH],    AUTHORITY["EPSG","3857"]]   Any idea? D3
64290
I have raster displaying Lat/ Long grid, but map information shows that, it s been mapped in Gauss Krugger projetion/ Beijing 1954. So, technically we need to geo reference the map in Gauss Krugger/ Beigjing 1954 Projectec Coordinated System in ArcGIS.   So, basically what I need to do is, georeference raster by input of Lat/Long, but need to update the georeferencing by projected coordinated system mentioned above.  In Global mapper, we can load the raster and enter Lat/Long available in the map, straight away it will be recalculated to Projected coordinated system.   Can we get anything same in ArcGIS?
95327
The ultimate question, I need a transformation matrix to take a point in local space representing a roughly 500m x 500m place in New Mexico centered at -108.619987456 long 36.234600064 lat.  The final output needs to be in geocentric coordinates and I can during initialization get any number of points on the map such as the corners, center, western most along the center etc.  During run time I would like to have a transformation matrix that can be applied to a position in local space expressed in meters and get back an approximate GCC coordinate.  The center of the point in GCC: -1645380 -4885138 3752889 The bottom left corner of the map in GCC: -1644552, -4881054, 3749220  During run time I need to be able to multiply (-250, -250, 0) with the transformation matrix and get something close to (-1644552, -4881054, 3749220).  I've spent more than a week trying to research a solution for this and so far nothing.  Given an identity matrix as our starting position and orientation. Then using geotrans and the known lat, long, and height of the starting position I get an x,y,z geocentric coordinate. A vector from the origin of (0,0,0) gives both the up and translation for the matrix. However, I need the forward and right so that I can pass a distance in meters from the origin into the transformation matrix and get a roughly accurate GCC. Do I have all of the inputs I need to calculate the right and forward?  Inputs Origin: 0, 0, 0 Global: -1645380, -4885138, 3752889 Up (Normalized): Global - Origin  Desired Outputs Right: ? ? ? Forward: ? ? ?  So with the right and forward added to the up and translation I already calculated I would have a transformation matrix.  I could then apply the matrix to a vector of say (50, 50, 0) and get something within about 0-3 cm of the output if I feed the lat/long back into geotrans.  This matrix would only ever be used small maps of about 500m x 500m so the curvature of the earth is negligible.  In reply to whuber,  I don't know your level of experience so I will start with the very basics.  An identity matrix is a 4x4 matrix that you can multiply by a vector and it returns the vector unchanged. Such as below.  1 0 0 x=0 0 1 0 y=0 0 0 1 z=0 0 0 0 1  The x, y, and z of the matrix are how much to translate the vector by and the first 3 rows and columns are the rotation.  Below is a tranformation matrix that does nothing to the orientation of a vector but does translate.  This is what you would want for two axis aligned worlds in different locations.  1 0 0 13 0 1 0 50 0 0 1 -7 0 0 0 1  If you were to multiply a vector of (10, 10, 10) with the above transformation matrix you would get an output of (23, 60, 3).  My problem is the axes are not aligned and the "plane" of the world I am trying to get the local coordinate converted to is projected on the ellipsoid of the earth.  Geotrans is library that you can use to pass a coordinate from one system such as geodetic or GDC (lat, long, height) and get back another such as geocentric or GCC (x,y,z).  For example: If my game world was representing a map centered exactly on the prime meridian and equator the transformation matrix would look something like below. I am just guesstimating the Y and Z rotations and might have them flipped and/or the wrong sign.    0 0 1 6378137 0 1 0 0 1 0 0 0 0 0 0 1
42945
There are few ways of articulating my question. It starts with a known circle on a sphere, i.e. a point-radius, and one that does not cover a pole.  I would like to calculate the point furthest west on this circle and the point furthest east. These points are the tangent points of lines of longitude which encircle the poles and are vertical.  These points are opposite each other along the vertical axis so there is one hard problem to solve from which the other is trivially determined.  This is highly related to calculating the minimum bounding lat-lon box of a circle.  I know how to determine the longitude delta from the center to the edges, which is:  asin( sin( dist_rad / cos(center_lat_rad) ) )   whereas dist_rad is the circle's radial distance is radians, and center_lat_rad is the latitude point of the circle's center in radians.  This equation was elusive to me until I discovered it with a wonderful explanation .  It contains a wonderful illustration:  .  The illustration shows T1 and T2 which are the points I am trying to calculate. What is left to figure out is at what latitude the eastern and western boundary meridians intersect this circle.  If the circle is at the equator, then it's zero, and if it's north of the equator, then this latitude is going to be higher than the circle's center latitude.
20653
I am using GeoServer and have a layer in EPSG:900913 ("Google Mercator").  I need to "rotate" the map around certain point (say, 1500000, 7000000) by certain degree (say, 30 degrees clockwise). How could I define such a coordinate system based on EPSG:900913?  GeoServer's  does not work for my purposes as I need to tile the map later on.  As far as I understand this, my only option is to define an own coordinate system. For GeoServer I'd need to . The configuration seems to be straightforward, but I have a difficulty defining my rotated CRS in .  I am wondering how to apply a rotation around certain point onto a CRS like Google Mercator:  PROJCS["WGS84 / Google Mercator",    GEOGCS["WGS 84",      DATUM["World Geodetic System 1984",        SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]],        AUTHORITY["EPSG","6326"]],      PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],      UNIT["degree", 0.017453292519943295],      AXIS["Longitude", EAST],      AXIS["Latitude", NORTH],      AUTHORITY["EPSG","4326"]],    PROJECTION["Mercator_1SP"],    PARAMETER["semi_minor", 6378137.0],    PARAMETER["latitude_of_origin", 0.0],    PARAMETER["central_meridian", 0.0],    PARAMETER["scale_factor", 1.0],    PARAMETER["false_easting", 0.0],    PARAMETER["false_northing", 0.0],    UNIT["m", 1.0],    AXIS["x", EAST],    AXIS["y", NORTH],    AUTHORITY["EPSG","900913"]]   My questions, specifically:   How to write a WKT which transform an existing CRS? My guess would be that I need a new PROJCS wrapping an existing one and adding a PROJECTION clause. How would I found out the projection id (like Mercator_1SP above) and the required parameters (the PARAMETER clauses)? Can I "reference" EPSG:900913 in CRS WKT instead of copy-pasting the whole PROJCS clause?
41318
I'm working on a school project. I have  from Sacramento, California   I want to convert the XY coordinates to latitude and longitude, in order to import it into tableau and use its mapping features.   I also have the address, if that makes it easier.  I have about 10,000 records, so I need a powerful tool to perform this conversion.
98398
What is the formula for the Nicolosi Globular projection? In other words, what is the function that maps the coordinate (φ, λ) on the sphere to the coordinate (x, y) on the plane?   You can assume that there are two such functions, one for each of the two hemispheres of the projection, such that the origin (x = 0, y = 0) in both cases is in the center of the given hemisphere.  Example of a Nicolosi Globular projection:
108778
I have a non-georeferenced vector layer that I need to be georeferenced. With raster layers the task is easy and straightforward, but I have no idea what should I do with my vector layer. I have a few control points with known coordinates which should provide some basis to transformation. So, let's say I know points with id-s of 1, 2 and 3 should have the coordinates of x1,y1 ; x2,y2 ; x3,y3. There might be some rotation and scale transformation in addition to simple shifting.   Any ideas?
8672
I am considering the unit sphere (but an extension to one of radius $r$ would be appreciated) centered at the origin. Any coordinate system will do, though the standard angular one (with 1 radial and $n-1$ angular coordinates) would be preferable.   I know that on the 2-sphere we have $ds^2 = d\theta^2+\sin^2(\theta)d\phi^2$ (in spherical coordinates) but I'm not sure how this generalizes to $n$ dimensions.  Added note: If anything can be discovered only about the determinant of the tensor (when presented in matrix form), that would also be quite helpful.
38752
I'm researching non-Euclidean geometry.  Now I am looking for a good source for it.  Please suggest me something.Thanks.
110907
I have a perspective projection.  When the user clicks on the screen, I want to compute the ray between the near and far planes that projects from the mouse point, so I can do some ray intersection code with my world.  I am using my own matrix and vector and ray classes and they all work as expected.  However, when I try and convert the ray to world coordinates my far always ends up as 0,0,0 and so my ray goes from the mouse click to the centre of the object space, rather than through it.  (The x and y coordinates of near and far are identical, they differ only in the z coordinates where they are negatives of each other)  GLint vp[4]; glGetIntegerv(GL_VIEWPORT,vp); matrix_t mv, p; glGetFloatv(GL_MODELVIEW_MATRIX,mv.f); glGetFloatv(GL_PROJECTION_MATRIX,p.f); const matrix_t inv = (mv*p).inverse(); const float     unit_x = (2.0f*((float)(x-vp[0])/(vp[2]-vp[0])))-1.0f,     unit_y = 1.0f-(2.0f*((float)(y-vp[1])/(vp[3]-vp[1]))); const vec_t near(vec_t(unit_x,unit_y,-1)*inv); const vec_t far(vec_t(unit_x,unit_y,1)*inv); ray = ray_t(near,far-near);   What have I got wrong?  (How do you unproject the mouse-point?)
82953
I'm trying to georeference a picture using Latitude and longitude. The points are these:  top-left:  (116.30950927734372,39.970805680527725)   top-right:  (116.35620117187497,39.970805680527725)   bottom-left (116.35620117187497,39.93606595478707)   bottom-right (116.30950927734372,39.93606595478707)    When I tried to calculate the area of a polygon,the result is very small(something like e-7).I realized to my horror that the QGIS had treated the Unit as meter.What should I do?  (QGIS1.8)
21645
the point represents rates like 10%, etc. (this was also pretty clear from 2 years ago) -- been trying to do this for 2 yrs...  the points dont represent numbers of events since they are rates ()    but the points have geo ids so they are attached to location, not distance (whatever distance is to imply) -- update: it represents z-value but we're just dealing with rates
23756
If you have a 2D vector expressed as x and y, what's a good way of transforming that into the closest compass direction?  e.g.  x:+1,  y:+1 =&gt; NE x:0,   y:+3 =&gt; N x:+10, y:-2 =&gt; E   // closest compass direction
32583
I don't know so much about coordinate systems...  In my office we use to deal with spatial data coming from archaeological sites. Each site has its own x-y-z coordinate system (GCS). Three simple ortogonal cartesian axis. In the last years we have been managing this spatial data through GIS software (ArcGIS), without using specific coordinate system (just leave it as "undefined")  I'd like to know if there exisits any GCS designed to deal with such datasets using simple cartesian orthogonal axis, without grid distortions of the typical GCS. In addition, I'd like to know if this system is suitable for using it in an online mapping application.  By the way, we manage 2D (ArcMap) and 3D (ArcScene) environments and work with "mm" as length base unit.   If such a thing doesn't exists, maybe someone knows how to create it.