Hot answers tagged wgs84
12
This question assumes an ellipsoidal model of the earth. Its reference surface is obtained by rotating an ellipse around its minor axis (plotted vertically by convention). Such an ellipse is just a circle that has been stretched horizontally by a factor of a and vertically by a factor of b. Using the standard parameterization of the unit circle,
t --> ...
11
Im a big fan of "preFeatureInsert"....
veclayer = new OpenLayers.Layer.Vector("vector", {
projection: map.displayProjection,
preFeatureInsert: function(feature) {
feature.geometry.transform(projWGS84,proj900913);
}
};
10
One simpler way would be to use the GDAL command line tools:
gdalwarp infile.tif outfile.tif -t_srs "+proj=longlat +ellps=WGS84"
That can be invoked easily enough via scripting for batch jobs. This will warp the raster to a new grid, and there are other options to control the details.
http://www.gdal.org/gdalwarp.html
The target (t_srs) coordinate ...
9
WGS-what? WGS-84? Depending on what accuracy you need, you may need to know a lot more information - my guess is that's why you've been down voted, though no-one bothered to leave a comment saying why.
Here are two ways:
Inaccurate, but probably 'good enough'
One degree of latitude is approximately 10001.965729/90 kilometres (distance from the equator ...
9
The geopy module provides the Vincenty formula, which provides accurate ellipsoid distances. Couple this with the wkt loading in Shapely, and you have reasonably simple code:
from geopy import distance
from shapely.wkt import loads
line_wkt="LINESTRING(3.0 4.0, 3.1 4.1)"
# a number of other elipsoids are supported
distance.VincentyDistance.ELLIPSOID = ...
8
As mdsumner said, it's much easier to use command line than the python bindings, unless you want to execute very complex tasks.
So, if you like python, like I do, you can run the command line tool with:
import os
os.sys('gdalwarp infile.tif outfile.tif -t_srs "+proj=longlat +ellps=WGS84"')
or iterate through a list o files:
listoffiles=['file1, file2, ...
8
PyProj assumes that your coordinates are in meters. I'd guess something relating to feet/meters is the cause of the issue.
Calling a Proj class instance with the
arguments lon, lat will convert
lon/lat (in degrees) to x/y native map
projection coordinates (in meters)
If the optional keyword
'preserve_units' is True, the units in
map ...
7
WGS-84 is unprojected data. It uses a geodetic coordinate system, which means points are located on a spherical (ellipsoidal to be exact) modelisation of the earth.
As a consequence, euclidian geometry is not valid for this kind of data.
PostGIS «geometry» data type and associated functions work with planar coordinates and euclidian geometry computations. ...
7
Here EPSG:32616 WKT, both are same
PROJCS["WGS 84 / UTM zone 16N",
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 longitude", EAST],
...
6
I get the same results as @geographika when I run gdaltransform and the proj.4 tool cs2cs:
$ gdaltransform -s_srs EPSG:3734 -t_srs EPSG:4326
739400.9 2339327.3
-87.3195485720169 45.9860670658218 0
cs2cs +proj=lcc +lat_1=41.7 +lat_2=40.43333333333333 +lat_0=39.66666666666666 +lon_0=-82.5 +x_0=600000 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=us-ft ...
6
GDAL runs on most platforms, including Windows, so I'm not sure where you get the idea it only runs on Macs! The easiest way of getting installed on your machine is to download OSGeo4W, which is an installer for all manner of desktop GIS goodness, from which you can just choose GDAL/OGR.
Once you've done that, you can use the command line tool gdalwarp to ...
6
As om_henners advised it is better to use available library for this purpose as it is already implemented and tested by many people...
So, take a look at pyproj Python lib.
Here is a sample code for reprojecting WGS-84 long/lat to ITM (EPSG:2157) x,y:
from pyproj import Proj, transform
def reproject_wgs_to_itm(longitude, latitude):
prj_wgs = ...
6
You have a closing paren in the wrong place towards the end of your query. I tried this and got a NaN return,
SELECT ST_AREA(ST_Transform(ST_GeomFromText('POLYGON((871325.790874952 6105405.3261047,871418.748307692 6105359.72944624,871346.22022442 6105215.141258,871254.85408906 6105261.72007212,871325.790874952 6105405.3261047))',4326),31467)) As sqm;
...
5
What you're looking for is an equal-area projection, and ideally one which also partially preserves shape. In the past, I've used the USGS projection DSS to help guide these decisions, it'll walk you through a process of choosing a good projection. More generally, tools like Flex Projector and Tissot's Indicatrix should help guide a decision: they provide ...
5
Here is the really easy way. Add a field to your existing feature class. Right click on the field title and choose "Calculate Geometry". You'll then have the option to pick your desired coordinate system and units of measure.
One note: This calculation is static, so you will need to recalculate anytime you make changes.
5
Open Layers uses the term 'EPSG:4326' to mean the Plate Caree projection. Referring to 'WGS84' and EPSG:4326 as a projection has been common for so long that it is a source of confusion. This short-hand has been going on since before Google and OpenLayers came on to the scene. For instance, ESRI have been fudging the terms for as long as I can remember. ...
4
You can temporally re-project the data on the fly in arcmap and use
CTRL+SHIFT+G to open the Calculate Geometry dialog box
and calculate the area with the current projection (meter/feet)
after the field is populated you can go back to WGS84 but the area will remain (unless you recalculate the area again)
4
I like MerseyViking's answer but would suggest a slightly different workflow, still using FWTools though.
Define the LCC projection:
if nonstandard, define projection by adding definition in epsg file of proj4. See this article for an example.
Merge all 30 images into a virtual mosaic:
most easily done in GDAL using a VRT
Create tiles in (Google) ...
4
You can compare the two. In most applications I suspect the second (direct) method will be the one to choose.
Accuracy of the first (iterative) method depends on the accuracy with which you do the computations and when you decide to stop iterating. It therefore can be made as accurate as the second method for all inputs where both are valid (the first ...
4
Sightings constitute a (non-random) sample of some process or population. Accordingly, interpolation (especially) IDW is not a good idea: it solves a different problem altogether.
Consider making a density map. When doing so, it's probably better to favor equal-area projections over conformal projections (because changes of area bias the density, whereas ...
4
The coordinate format is not SpatiaLite specific - its WKT, and the meaning depends on the spatial reference system. In this case you're using EPSG:4326 which is WGS84 Longitude - Latitude. So the first coordinate is degrees of longitude and second is degrees of latitude, referenced from the WGS-84 origin.
The insert looks OK, but something is obviously ...
3
Took ASPMapper's approach but instead of doing math on my own, used geodesic package from PROJ.4 (python binding pyproj, http://code.google.com/p/pyproj/).
from pyproj import Geod
minX = -74.002747535706 # in degrees
minY = 40.722282672831
maxX = -73.98386478424
maxY = 40.733470232685
distance = 100 # in meters
g = Geod(ellps='WGS84')
coords = []
...
3
It's a good question, because gridding lat-lon usually introduces tremendous distortions and often they can be avoided. However, the answer depends on the analysis. Not all analyses need equal cell sizes. Many times you can weight a grid calculation to compensate for variable cell sizes: the appropriate weighting factor is the cosine of the latitude. ...
3
Have a look at the paper "A COMPARISON OF EQUAL-AREA MAP PROJECTIONS FOR REGIONAL AND GLOBAL RASTER DATA" http://carto-research.er.usgs.gov/projection/pdf/nmdrs.usery.prn.pdf which should help answer your question.
3
It's simple but messy.
Because you're working in ECEF, presumably you have the ray's origin (x,y,z) and direction vector (u,v,w) in ECEF coordinates, too. For the moment let's assume that during the time of travel to the earth's surface, the earth does not appreciably move. (The fastest part of the rotating earth, the Equator, moves about 0.45 km/sec and ...
3
Just done the process for Cambridge. [This is the fastest method]
Using PostGIS 2.0 (pgAdmin postgres SQL Tools 1.14)
Downloaded the Cambridge OpenStreetMap data from here:
http://download.geofabrik.de/osm/europe/great_britain/england/
selected Cambridge note the cambridgeshire.shp.zip 01-May-2012 06:08 11M ESRI Shapefile (EPSG:4326), zipped
Loaded ...
3
The shp2pgsql tool is used to load data into PostGIS. It is not meant for transforming projections. The -s flag of the command just tells shp2pgsql the SRID of your source data. It doesn't transform the projection at all. You can reproject it before you load it to PostGIS or after.
To transform the projection before you load it to PostGIS, you can use GIS ...
3
Hey I think this is your answer to the question:
http://www.quickclose.com.au/stanaway07pres.pdf
Dont know if it really helps but it does state what each is and that WGS is regularly aligned to ITRF.
Basically as you know, two types of Co-ordinate reference system.
3
This is not WGS84 System, WGS system is an angular system so the latitude value cannot exceed 90, and the longitude can not exceed 360. You need to figure out the coordinate system of your data, which i guess might be in WGS84 projected system which measures distance in meters. Any GIS softwares can convert it e.g. Quantum GIS.
Roughly: 3 sec in WGS84 ...
2
You could try the .NET library Proj.Net. See the Loading a projection by Spatial Reference ID page for how to add in the GB National Grid.
Example code from this forum post:
CoordinateSystemFactory c = new CoordinateSystemFactory();
ICoordinateSystem target = c.CreateFromWkt("PROJCS[\"OSGB 1936 / British National Grid\",GEOGCS[\"OSGB ...
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