I have trying to get Latitude and Longitude of a Point.
But While transforming it's not returning the correct LonLat. It's big number that is not a lonlat point for sure.
I have tried for some solutions but didn't get result.
What else could be failing?
JS Code I have Tried
map = createMap("deviceMap");
var fromProjection = new OpenLayers.Projection("EPSG:4326");
var toProjection = new OpenLayers.Projection("EPSG:900913");
map.events.register('click', map, function handleMapClick(e) {
lonLat = self.map.getLonLatFromViewPortPx(e.xy).
transform(map.getProjectionObject(), toProjection);
prompt("",lonLat);
});
Finally got answer
map.events.register('click', map, function handleMapClick(e) {
var toProjection = new OpenLayers.Projection("EPSG:4326");
var lonLat = map.getLonLatFromPixel(e.xy).
transform(map.getProjectionObject(), toProjection);
});
EPSG:4326
should refer to WGS 84,
has decimal degree values
EPSG:900913
refers to WGS84 Web Mercator
has metric values, it is x/y axis coordinate system, so "high numbers" are expected
If I understand you right, you should have in variable lonLat a high number.
"LonLat" in OpenLayers does not mean, it will be only longitude/latitude, see documentation here:
lon {Number} The x-axis coordinate in map units. If your map is in a
geographic projection, this will be the Longitude. Otherwise, it will
be the x coordinate of the map location in your map units.
lat {Number} The y-axis coordinate in map units. If your map is in a
geographic projection, this will be the Latitude. Otherwise, it will
be the y coordinate of the map location in your map units.
So if you want to get a real LonLat coordinates, you should not convert it (and use EPSG:4326) or convert it to the other coordinate system, not EPSG:900913.
By the way, OpenLayers started to use 900918 (numeric equivalent to GOOGlE), It was define by Mr. Christopher Schmidt, firstly it was not accepted by European Petroleum Survey Group (EPSG). Then EPSG changed their mind and gave them number: 3857 - WGS84 Pseudo-Mercator.
Related
I'm not too familiar with the D3 mercator projection function, and I'm getting some unexpected results. I'd like to project the following latitude and longitude (somewhere in Mexico):
var geo = [19, -99]
I define my mercator projection using d3
var projection = d3.geo.mercator();
projection(geo)
> [529.7418836818384, NaN]
which is a point obviously not on a map. What exactly am I doing wrong? Thanks!
Javascript has it's lat and long round the opposite way to the rest of the world, so what you've given D3 is a longditue of 19 and a latitude of -99. Obviously there is no latitude of -99 hence the NaN. Now if you just reverse your geo variable to
var geo = [-99, 19]
all should be good.
I want to use decimal Lon and Lat like Google Maps uses. But it seems I need to transform the LonLat object in OpenLayers, e.g.
var map, layer;
function init(){
map = new OpenLayers.Map('map');
layer = new OpenLayers.Layer.OSM( "Simple OSM Map");
map.addLayer(layer);
map.setCenter(
new OpenLayers.LonLat(-1.60400390625, 54.07228265560386).transform(
new OpenLayers.Projection("EPSG:4326"),
map.getProjectionObject()
), 6
);
var markers = new OpenLayers.Layer.Markers( "Markers" );
map.addLayer(markers);
var size = new OpenLayers.Size(21,25);
var offset = new OpenLayers.Pixel(0,0);
var icon = new OpenLayers.Icon('http://www.openlayers.org/dev/img/marker.png', size, offset);
markers.addMarker(new OpenLayers.Marker(new OpenLayers.LonLat(-1.60400390625, 54.07228265560386).transform(new OpenLayers.Projection("EPSG:4326"),map.getProjectionObject()),icon));
}
Each time I place a marker the position needs to be transformed to EPSG:4326. Is there a way to tell the map to always use this projection?
Whether you can set the projection on a map or not, depends on which service you are using for the base layer. As far as I know, OSM only provides its rendered tiles in EPSG:900913, so there is no way around transforming your coordinates before adding them to the map. You could search for a service that provides its tiles in multiple projections, but I haven't seen one that is free to use so far. An alternative would be to render your own tiles in the needed projection and provide them through your own tile server.
Let's suppose you have such a map, you can change the projection using OpenLayers.Map.setOptions() like this:
map.setOptions({
projection: "EPSG:4326"
});
But you may also need to set some projection related properties, like maxExtent etc. See this question.
I'm trying to get the latitude/longitude from a draggable marker with Openlayers and OSM but I can't find the good settings for the projection conversion, what I am doing wrong ?
Here is the code: http://pastie.org/2300321 (see addMarker l140 & updateTargets l153) & and a little demo test.
If you submit an address, then drag the marker, the longitude and latitude are wrong. I tested a few different projections but I'm not sure what I've to use…
I think the problem is inside updateTargets method:
var point = this.feature.geometry;
var pixel = new OpenLayers.Pixel(point.x, point.y);
var coord = this.map.getLonLatFromPixel(pixel).transform(
new OpenLayers.Projection("EPSG:900913"),
new OpenLayers.Projection("EPSG:4326")
);
this.feature.geometry is already specified in lon/lat coordinates, not in pixels. So I suggest that you skip second line and do the conversion from OpenStreetMap projection to lon/lat directly on geometry object:
var coord = this.feature.geometry.transform(
new OpenLayers.Projection("EPSG:900913"),
new OpenLayers.Projection("EPSG:4326")
);
In Javascript.
I have a map of the world that is 1024 x 1024px - It is a spherical Mercator projection.
Im looking to convert long/lat to x,y for this map. I have a bunch of coordinates that I need to overlay on top of it.
Calculating longitude was very easy, and I am doing it like so:
pos.x = ((long + 180)/ 360) * 1024;
I just need to same for lat --> y
I looked around a saw a lot of reference to openlayers, but didn't see such a conversion.
To boil it down:
var mercator = function(lat, lng) {
return [lng, Math.log( (Math.sin(lat) + 1.0) / Math.cos(lat)) ] ;
};
Lat and long must be expressed in radians of course.
You can find the corresponding formulas in this wikipedia article: Mercator Projection.
I have polyline in my map. I want to know the pixel (screen) xy-coordinates, when user clicks the polyline. Click event only returns the LatLng object, so does anyone have a clue how to get the pixel coordinates from latLng?
I would appreciate very much if someone could help me!
If you have the LatLng object, you can use the google map projection object to transform it into tile coordinates and then into pixel coordinates:
For the docs on the projection class:
https://developers.google.com/maps/documentation/javascript/reference#Projection
Google's example explaining how to transform a LatLng into a pixel coordinate:
https://developers.google.com/maps/documentation/javascript/examples/map-coordinates?csw=1
There's one catch. The above will give you the pixel coordinates inside google's map div (which you may want depending on your needs). If you want the pixels relative to the top left corner of the screen, there's one more step. You need to do the same projection on the the viewport's top left corner and subtract the two. This will give you the pixel coordinates of the LatLng point.
The code I finally used looked like this (note that "latLng" is an input):
var numTiles = 1 << map.getZoom();
var projection = map.getProjection();
var worldCoordinate = projection.fromLatLngToPoint(latLng);
var pixelCoordinate = new google.maps.Point(
worldCoordinate.x * numTiles,
worldCoordinate.y * numTiles);
var topLeft = new google.maps.LatLng(
map.getBounds().getNorthEast().lat(),
map.getBounds().getSouthWest().lng()
);
var topLeftWorldCoordinate = projection.fromLatLngToPoint(topLeft);
var topLeftPixelCoordinate = new google.maps.Point(
topLeftWorldCoordinate.x * numTiles,
topLeftWorldCoordinate.y * numTiles);
return new google.maps.Point(
pixelCoordinate.x - topLeftPixelCoordinate.x,
pixelCoordinate.y - topLeftPixelCoordinate.y
)