Tag Info

New answers tagged

2

Set lon_0 to the middle of your study area. k can be set to 0.9996 (as UTM has). lat_0, x_0 and y_0 have no effect on the quality of the projection. They are usually set to the equator and/or the inverse of the lower left point so that all coordinates are positive.


3

There is a bug in the Project Raster Tool. The output raster from the Project Raster tool is a little too big on the eastern edge, and on the southern edge (bottom of the easternmost gore/lobe). So the data extent doesn't quite match what the extent of a Goode's Homolosine projection is, and triggers the "not consistent extent" warning. A workaround is to ...


1

There's an svg of this projection on wikipedia. All country codes in main map group and easily editable in illustrator https://commons.wikimedia.org/wiki/File:Perlshaper_Winkel-Tripel_example1.svg#/media/File:Perlshaper_Winkel-Tripel_example1.svg


0

well the winner is to not use the = sign. this works for anyone looking.. ogr2ogr -overwrite -t_srs EPSG:3978 -f "ESRI Shapefile" -dialect SQLite -where "GIVEN_CLASS LIKE 'CLAS% A" dst src indicating dialect + using -where + Like operator.


2

The official definition for EPSG:3857 is +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs As you see, it is calculated on a sphere (a=b). Your formula is a bit contradictory: You define a lat-long coordinate system on the WGS84 ellispoid, then you add +init=epsg:3857 which should ...


2

You can pull this out of the DBs that ship with GeoTools as well. There is a method on CRS for it whose name escapes me but should be obvious.


4

You can download the EPSG data from http://www.epsg.org/DownloadDataset after you register. No cost to register, and no delay between registration and download. There are two formats that might be useful - a set of PostgreSQL scripts (also other databases, but PostgreSQL is the one I checked) that insert data, so you can do a query of the epsg_area table. ...


4

Download the MS Access database and/or the polygon shapefiles from the EPSG Geodetic Dataset Registry (upper right, "export registry"). You do have to register, but we don't spam or sell the list of registered users. The MS Access database contains the rectangular extent areas of use only. Or you can download the files from the OGP website, same login ...


1

Ok, I've figured it out. It is possible to apply an affine transform onto some existing CRS using FITTED_CS. Below is an example of rotation of 60 degrees counterclockwise and movement: FITTED_CS["BPAF", PARAM_MT["Affine", PARAMETER["num_row", 3], PARAMETER["num_col", 3], PARAMETER["elt_0_0", -0.5], PARAMETER["elt_0_1", ...


0

The "Without PoK" data is a shapefile that has been converted from an image. The shapefile extents are (0,0) and (1496,1497) which represent the cell/pixel sizes of the original image. If you have the original image, you could try georeferencing it directly to your other data. Otherwise, you could try using the Spatial Adjustment toolbar, again to ...


1

You can define a local rotated coordinate sytem as I explained here: Using customized Coordinate System for Archaeological site data Center point and rotation have to be defined in degrees. Your idea of wrapping one projection with another is not defined in PROJ.4. You can try it out, but don't expect it to work.


2

While not fish eye, you can make this style of map as a cartogram. The benefits of this is that there are ready made tools for the job and will work with a robust set of datasets. Just make the value for the Czech Republic much larger than the rest of Europe, adjusting the values to suit needs. A great tool for this is: ScapeToad


3

Here's a pseudo-fisheye done in Postgres/Postgis. I used QChainage plugin to create 1000 points along each country border. The points were reprojected around null island (0,0) using the logarithm of distance, but with azimuth preserved. I used Plat Caree to make it circular, as wgs84 gives a more ellipsoid appearance. select st_asewkt( ...


0

I think you will need an extreme distortion for the Czech Republic to look like that. There is a fairly popular photographic "stereographic projection" technique sometimes used in panorama photography to create "globe worlds" which may work if you used the result as overlay over Europe. (Do not consider this an answer as this is purely hypothetical and I've ...


5

You might try one of Snyder's Magnifying Glass projections found on http://www.csiss.org/map-projections/Azimuthal.html No 32 to 36. They are based on this publication: https://pubs.er.usgs.gov/publication/70014498 I'm not sure if there is an online resource with the formulas. Hägerstrand’s Logarithmic Map might also fit your needs: ...


1

@whuber's assertion that an equal-area projection "will give absolutely correct areas" comes with an asterisk, namely, assuming that the edges of the polygon are straight lines in said projection. This is often a good approximation, particularly if the edges are short; but it is rarely strictly true. If, on the other hand, the edges of your polygon are ...


1

D3 has a fisheye distortion plugin, which I found by Googling "svg fisheye transform".. It might be useful for your situation. Basically, I'm suggesting converting some of your shapefiles to SVG (or GeoJSON?) making your map using the increasingly popular D3.js library. My thinking was, I knew the country boundary geometries could be converted to SVG vector ...


1

It depends on the use case of your application. Make some considerations: Raster warping is not supported by OpenLayers. Is your map server propagating layers also in EPSG:4326? If not, you cannot use that projection. Is high coordinate precision a necessity? Transforming coordinates usually come with some minor distortions as a ramification of rounding. ...


1

NAD83(CSRS) (which is based on ITRF96(1997.0)) is not a simple transformation away from WGS84. It's anchored to the North American plate, which is rotating counter-clockwise, and uplifting -- in some places rapidly -- due to isostatic rebound. Proj doesn't know anything about this. It can transform from geographic to geocentric and UTM, and it can shift from ...


1

You were are actually converting from EPSG:4917 (ITRF96), not EPSG:4326 (WGS84). See the TRX online utility from NRCan to do this conversion: Unfortunately you cannot use PROJ.4 to convert ITRF projections; see enhancement ticket #154. If you were using WGS84 in place of ITRF96, then your steps with pyproj were fine. However, if you need ITRF96, then ...


7

"EPSG:3488, EPSG:NAD83(NSRS2007) / California Albers" is an equal-area projection. It is based on the Albers Conic, which is defined for the northern hemisphere. Because Sweden is within its range of definition, it is equal-area in Sweden. This means that (up to floating point rounding error) it will give absolutely correct areas. Neither the Mollweide ...


1

Geodetic area calculations are not part of GDAL. You would probably need to write your own function to do it and exact solutions are computationally intensive. You're better off using an Equal-Area projection, such as Albers, Azimuthal, or Lambert azimuthal (https://en.wikipedia.org/wiki/Category:Equal-area_projections). For largish regions in Africa, ...


3

The length of degree in north-south is about the same so you could use 1/110574 degree/meter as a factor. However, the farther to south or north you go the bigger the error is in east-west direction. For example, take these two shapes which have a 1 degree buffer in EPSG:4326 transformed into EPSG:32630 (UTM zone 30N). First one is from 40°N and the second ...


0

The WGS84 geoid is not a sphere with a constant radius, but rather an ellipsoid. According to https://en.wikipedia.org/wiki/World_Geodetic_System, the ellipsoid has a = 6378137 m and b = 6356752 m. It seems that without OTFR the distance is calculated using the sphere, and with OTFR using the ellipsoid.


1

The following code might seem a little long-winded as it represents a manual approach rather than relying on OpenStreetMap, but maybe it's of any help to you anyway. I took the country boundaries and the referring country labels from the wrld_simpl dataset (class 'SpatialPolygonsDataFrame', projected in EPSG:4326) that comes with maptools. The shapefile data ...


4

I don't think you get what the problem is at all. The problem is that the earth is curved; It isn't an sphere; It's not an oblate spheroid, it an even more complex shape, called the Geoid. And whenever you try to go from this Curved shape to a flat plane (like the paper you are talking about) you will have some or the other distortions. That is why ...


2

If you reproject a raster with labels, you will obviously get squeezed labels. The only way to avoid this is to render the raster from vector data directly into the desired projection. You might want to look into mapnik, tilemill or maperitive to do this from Openstreetmap raw data (which is vector data). The R openstreetmap package only offers raster ...


2

If you build a local transverse mercator CRS where lon_0 and lat_0 is in the center of your scene, you will have true distances within 5 kilometers: +proj=tmerc +lon_0=7 +lat_0=51 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +towgs84=0,0,0,0,0,0,0 +no_defs It should work in the ARCGIS world just the same.


1

No, it's not possible at the moment. Maps within the composer will always use the same projection as the main map canvas.


1

Maybe you should re-save again your data (right click on the layer,save as).. this time make sure you change the crs which has distance unit (e.g wgs 84 world mercator - meter units). This new layer should have new distance unit. You can check again whether you already use the right crs through metadata (you can also use qgis browser)


0

As a potential starting point for a list of differences it might help to see my new PyCRS package, where I have attempted to create a class for each crs element, parameter, and datum/ellips/proj name, along with their esri_wkt vs ogc_wkt spelling. I have also specified how I see the parsing differences in terms of the wkt structure as a whole in the ...


0

It seems to me your question has two parts--1) what do the tags tell you about the coordinate system, and an implied 2) how to extract positional data based on the image's coordinate system. TAGS: L_Holcombe is right, in that the PCS (projected coordinate system) holds an EPSG code for the coordinate system that is supposed to describe the image. I prefer ...


1

The info tool only displays the tabular data stored in the file. This is NOT linked to the spatial data so any changes to the spatial data may require an update of the tabular data in order for the two to agree. In addition, check the projections of the session, map window, and table. You can ensure that the map window and session are using the same ...


1

Rightclick -> Saxe As ... to reproject a layer only works for vector layers. Raster layers are a bit more complicated, you have to use Raster -> Projections -> Warp(Reproject) with a new file name and source CRS different from target CRS.


1

I always prefer coordinates in latlon WGS84 because they are usable worldwide and easy to understand once you know which is latitude and which is longitude. I happen to live in a country that spans across several UTM zones, and before that used several smaller Gauss-Krueger zones. As long as you are within one zone, everything is ok, but cross-zone ...


0

From a visualization point of view I was though you should use projected coordinate systems for even things on a US State size scale. Any size State that is broken into multiple State Planes, looks best in a Web Mercator or WGS projection. When you get to a region or city level, most data looks a little better in a state plane or utm projection.



Top 50 recent answers are included