Hot answers tagged coordinates
29
The terms are medieval:
latitude (n.) late 14c., "breadth," from Old French latitude (13c.) and directly from Latin latitudo "breadth, width, extent, size," from latus "wide," ... . Geographical sense also is from late 14c., literally "breadth" of a map of the known world...
In the fourteenth century, most known-world maps made in the Christian and ...
20
There can be some confusion over the difference between a Spatial Reference System (SRS) and a Coordinate Reference System (CRS), and unfortunately WGS84 is often used for both. EPSG:4326 is merely the reference number of EPSG's database entry describing a CRS. Typing 4326 into their website here gives us this:
The things to note here are that 4326 refers ...
15
Any equal-area projection will do the job well. There are loads of equal-area projections that cover the entire earth (minus a point or two). Many of them are versions of a Cylindrical Equal-Area projection (such as the Gall-Peters).
You don't have to permanently reproject your polygons: create a temporary copy of the layer if you like, reproject it, ...
14
This is tricky for two reasons: first, limiting the points to a circle instead of a square; second, accounting for distortions in the distance calculations.
Many GISes include capabilities that automatically and transparently handle both complications. However, the tags here suggest that a GIS-independent description of an algorithm may be desirable.
To ...
13
Yep sure can. Like alexgleith said you can use the qgsaffine plugin (from the plugin installer)
The top of the first line is at 0,0 and the top of the second line is at 5,5. At the start the points are along 0 on the X.
Using the Affine plugin we can add 5 to all the X coordinates:
Then after they are all on the second line at X 5, Y 5:
8
You have two tasks: (a) find the grid data for the vertices of a grid cell in which a GPS location (x,y) lies and (b) interpolate those data.
An efficient way to accomplish (a) is to store the grid as an array with a single index. Often grids are stored by rows with data progressing left to right within each row. A grid is determined by the coordinates of ...
8
Yes you can place a point at exact coordinates. There are a couple of ways you can do this. One is interactively by digitizing a point and then, while still in edit mode select the "Numerical Vertex Edit" button at the right hand end of the edit toolbar. You highlight a point and then type in the location in the popup box.
The other way, if you have ...
6
The Generate Conditional Random Points tool from Geospatial Modelling Environment should do the job for you. If you specify the BVUNIFORM option for the distrib atttribute (distribution) you can supply a radius around the input points within which new points will be generated in a uniform distribution. The number of points generated (the sample attribute) ...
6
In order to have the z value of your waypoints or tracks I usually use GPS babel. In Babel you can load a GPX file and then translate it to a csv file.
The resulting csv will have each point of the track or each waypoint with the altitude value
this is an example of what you can get.
Since it is a csv file, you can load it in to qgis with the "add ...
6
Open your point shape in QGIS
Check that the projection is right and open the "Export/Add Geometry Values" function in the vector menu -> Geometry tools.
This will add two columns to your point shape containing the exact coordinates.
Now you can export the attribute table to a external program. Here the easiest ways to do that
Select all points and simply ...
6
With EPSG:2227 NAD83 / California zone 3 (ft US) The result looks quiet good:
EPSG:2872 and 3494 have the same proj definition.
You can load the data as delimited text layer into QGIS, assign projection EPSG:2227 to it, and Rightclick -> Save As ... to WGS84 (EPSG:4326) under a different name. Just take care that usually x is positive East, and y is ...
5
You just need to re-project the geometry before displaying it:
var bounds = event.features[0].geometry.getBounds();
Should be:
var mapProj = map.getProjectionObject();
var epsg4326 = new OpenLayers.Projection("epsg:4326");
// OR in your case ...
// var epsg4326 = map.displayProjection;
var boundsNative = event.features[0].geometry.getBounds();
var ...
5
Hossein, combining spatial maps with databases is the heart of GIS. Practically any GIS will allow you to do both of those things in a variety of ways - though a desktop interface, programatically, served remotely, etc. Here is an excellent list of free and open source desktop GIS packages. Quantum GIS, with a powerful collection of tool and an easy-to-use ...
5
If you have your spatial data in a PostGIS database, try ST_AsSVG, e.g.:
postgis=# SELECT ST_AsSVG(ST_MakePoint(1797227.3141, 5431330.2559));
st_assvg
--------------------------------------------------
cx="1797227.3141000001" cy="-5431330.2559000002"
(1 row)
(The linestring and polygon conversions are much more tricky, and thus very ...
5
With coordinates that close to each other, you can treat the Earth as being locally flat and simply find the centroid as though they were planar coordinates. Then you would simply take the average of the latitudes and the average of the longitudes to find the latitude and longitude of the centroid.
Edit: As whuber points out, the above method would not work ...
5
In amateur (licensed) radio, this is routinely done using APRS, which you might research. It involves an interface from the radio to the PC, including a TNC (Terminal Node Controller). I suppose there is no reason it couldn't be adapted to non-licensed VHF frequencies. More detail about your need would enable me to help you more.
5
Just like any other function, you will get out the same unit of measurement you put in. In this example you are using lat/long and so will therefore get the distance between your two points (the hypotenuse) in degrees. The number of kilometers/miles/inches/whatever that the output corresponds to depends entirely on where on the surface of the earth the ...
5
I think you could do it simply in the attribute table. Firstly add fields with existing X and Y coordinates (if you don't have them already) by Add XY Coordinates (Data Management tools). Then you can add a new field and using Field calculator turned to Python you can create random values which you wish by the arcgis.rand() function (described in the help ...
5
I think the difference is likely due to the way that the Android phone with a GPS, and the iPhone using 3GS, are determining their location.
I am not sure about all Android phones, but it is likely that they are all using similar GPS for location purposes. This could be verified if you provided the similar models that you tested with. Anyway, the point is ...
5
Using SAGA-GIS you can use the tool Add Polygon Attributes to Points
On the commandline (linux or windows):
$ saga_cmd shapes_points 10
library path: C:\Program Files\SAGA-GIS\Modules
library name: shapes_points
module name : Add Polygon Attributes to Points
author : O.Conrad (c) 2009
Usage: 10 -INPUT <str> [-OUTPUT <str>] ...
5
In R, you can use my geonames package to access the www.geonames.org API:
> library(geonames)
Loading required package: rjson
Warning message:
In fun(libname, pkgname) :
No geonamesUsername set. See http://geonames.wordpress.com/2010/03/16/ddos-part-ii/ and set one with options(geonamesUsername="foo") for some services to work
> ...
4
If you want to move them manually, simply start editing, select the features you want to move and then select the move tool and shift them.
To move them by a particular x,y offset, you might be able to use the python plugin "qgsaffine".
I am not up to date with using the python console, but there is probably a solution there too.
4
I have done this when comparing collected GPS points to known positions. You want to use the distance formula Sqrt((x2 – x1)² + (y2 – y1)²).
What I did was to add two new columns (X2 and Y2) to my GPS points and populate those columns with the known X and Y coordinates. In my dataset I had the X and Y coordinates of my GPS data in columns X1 and Y1. ...
4
Depends on your accuracy requirements. One iteration of Heiskanen is efficient, but it takes 3 iterations to match the accuracy of a single iteration of Bowring's 1985 method. Even Lin and Wang's algorithm cannot match the efficiency of Bowring, if the trigonometric optimizations included below are used. Therefore, for all around performance I would ...
4
It looks to me like you need to perform the trigonometry in radians not degrees. You use a function toDeg() so presumably you have one called toRad() (or possibly fromDeg() if you're odd). Call that function with your latitude and longitude values before the calculations, and you should be set.
Edit
I just tried this in Python (the syntax isn't dissimilar ...
4
The only way that I know to visualize your data in 3 dimensions is using grass' nviz module which should be accessible via the qgis' grass plugin.
There are some video tutorials on the subject at youtube. For reference I am posting two of those:
http://www.youtube.com/watch?v=xn4nOhequgk
http://www.youtube.com/watch?v=ib1-mBbWkv4
4
The GeoNames API would be a good place to start if you are able to write a script to pull the data for you. There is a nice example, written in Python, in this github project.
You can also download the GeoNames data set here. Natural Earth also provides a data download.
4
I decided to develop a python script using the Nominatim tool by Open Streetmap to find the coordinates of the locations and it is working pretty good.
I made a screenshot, because for some reason, I am not able to add the code here:
There are some things you should not forget, when using this script:
According to the rules of Nominatim you should have ...
4
The coordinates reported on the bottom of the QGIS window are reported in the project CRS. That would be Web Mercator if you have OpenLayers loaded.
I guess you are expecting WGS84 (GPS) coordinates? You can use the coordinate capture plugin to get WGS84 coordinates independent of the project CRS.
4
A good guide and illustration into the process of Aerial Photography and Calibrating them to be correctly orthorectified
http://www.nrcan.gc.ca/earth-sciences/products-services/satellite-photography-imagery/aerial-photos/about-aerial-photography/891
Fiducial marks: small registration marks exposed on the edges of a photograph. The distances between ...
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