I want to use long/lat (EPSG:4326) coordinates in a bokeh plot and have a map in the Background.
I tried with the tile provider maps as suggested in bokeh: Mapping geo data.
But the format is in web mercator coordinates (EPSG:3857) and I don't want to convert my coordinates.
The general question how to do this is unanswered in Is it possible to set figure axis_type in bokeh to geographical (long/lat)?
My idea was to use extra axes:
from bokeh.plotting import figure, show
from bokeh.models import Range1d, LinearAxis
from bokeh.tile_providers import CARTODBPOSITRON, get_provider
tile_provider = get_provider(CARTODBPOSITRON)
p = figure(x_range=(-180, 180), y_range=(-90, 90)) # EPSG:4326
# add extra axis
p.extra_x_ranges = {"EPSG:3857x": Range1d(start=-20026376.39, end=20026376.39)}
p.extra_y_ranges = {"EPSG:3857y": Range1d(start=-20048966.10, end=20048966.10)}
# place extra axis
p.add_layout(LinearAxis(x_range_name="EPSG:3857x"), 'above')
p.add_layout(LinearAxis(y_range_name="EPSG:3857y"), 'right')
p.add_tile(tile_provider, x_range_name="EPSG:3857x", y_range_name="EPSG:3857y")
show(p)
But the map is not visible.
Is there a way to use extra axis for a tile_provider?
If you are just asking about displaying lat/lng visually on the axes, then all you have to do is set the axis type to "mercator"
p = figure(x_range=(-2000000, 6000000), y_range=(-1000000, 7000000),
x_axis_type="mercator", y_axis_type="mercator")
This is demonstrated on the documentation page you linked.
If you are asking about using data that is in lan/lng coordinates to plot on a tile plot, then you will need to convert it to Web Mercator first. The underlying coordinate system for tiles is always Web Mercator.
If you are asking about something else, then your question is not clear (please update to clarify).
Related
I'm using this example to import a polygon on an Openlayer map. However I'm having issues with the coordinate formatting. I'm importing the coordinates with a space as the delimiter with a carriage return between lines. I achieve success with a set of example coordinates from the Openlayers example. E.g. -
-5e6 6e6
-5e6 8e6
-3e6 8e6
-3e6 6e6
-5e6 6e6
This format works as it does in the example. However, when I use decimal degree format with the exact code that the examples uses this doesn't work. E.g. -
-83.6743 43.5857
-83.6743 44.0603
-82.4072 44.0603
-82.4072 43.5857
-83.6743 43.5857
Any suggestions would be appreciated.
Usually you would not want your view in EPSG:4326, so you transform the data from EPSG:4326 projection to display features in the view projection (which is usually EPSG:3857) as in https://openlayers.org/en/latest/examples/wkt.html
In the example by OpenLayers the Web Mercator Projection is used. You can see this from the key crs in geojsonObject:
'crs': {
'type': 'name',
'properties': {
'name': 'EPSG:3857',
},
},
"EPSG:3857" is the code for Web Mercator projection.
However, your coordinates are in the reference system WGS84 (code: "EPSG:4326"). Thus, you need to replace in the example "EPSG:3857" by "EPSG:4326". In addition, you have to adapt center and zoom in new View().
I have a SCNPlane that I created in the SceneKit editor and I want 1 side of the plane to have a certain image and the other side of the plane to have another image. How do I do that in the Scenekit editor
So far what I've tried to do is adding 2 materials to the plane. I tried adding 2 materials and unchecking double-sided but that doesn't work.
Any help would be appreciated!
Per the SCNPlane docs:
The surface is one-sided. Its surface normal vectors point in the positive z-axis direction of its local coordinate space, so it is only visible from that direction by default. To render both sides of a plane, ether set the isDoubleSided property of its material to true or create two plane geometries and orient them back to back.
That implies a plane has only one material — isDoubleSided is a property of a material, letting that one material render on both sides of a surface, but there's nothing you can do to one material to turn it into two.
If you want a flat surface with two materials, you can arrange two planes back to back as the doc suggests. Make them both children of a containing node and you can then use that to move them together. Or you could perhaps make an SCNBox that's very thin in one dimension.
Very easy to do in 2022.
It's very easy and common to do this, you just add the rear as a child.
To be clear the node (and the rear you add) should both use the single-sided shader.
Obviously, the rear you add points in the other direction!
Do note that they are indeed in "exactly the same place". Sometimes folks new to 3D mesh think the two meshes would need to be "a little apart", not so.
public var rear = SCNNode()
private var theRearPlane = SCNPlane()
private func addRear() {
addChildNode(rear)
rear.eulerAngles = SCNVector3(0, CGFloat.pi, 0)
theRearPlane. ... set width, height etc
theRearPlane.firstMaterial?.isDoubleSided = false
rear.geometry = theRearPlane
rear.geometry?.firstMaterial!.diffuse.contents = .. your rear image/etc
}
So ...
///Double-sided sprite
class SCNTwoSidedNode: SCNNode {
public var rear = SCNNode()
private var thePlane = SCNPlane()
override init() {
super.init()
thePlane. .. set size, etc
thePlane.firstMaterial?.isDoubleSided = false
thePlane.firstMaterial?.transparencyMode = .aOne
geometry = thePlane
addRear()
}
Consuming code can just refer to .rear , for example,
playerNode. ... the drawing of the Druid
playerNode.rear. ... Druid rules and abilities text
enemyNode. ... the drawing of the Mage
enemyNode.rear. ... Mage rules and abilities text
If you want to do this in the visual editor - very easy
It's trivial. Simply add the rear as a child. Rotate the child 180 degrees on Y.
It's that easy.
Make them both single-sided and put anything you want on the front and rear.
Simply move the main one (the front) normally and everything works.
I have spent dozens of hour trying to find is it possible to change projection with mapserver with no luck so far. My input format is EPSG 3067 and I need to convert it to EPSG 900913 for Google Map use.
In the MAP object add
PROJECTION "init=epsg:900913" END
this sets the output projection of the map. Then in t LAYER object add
PROJECTION "init=epsg:3067" END
this set the projection that the incoming data for the layer is already in.
You will also need to add the following line to your /usr/share/proj/epsg or the equivalent path if you are on Windows:
Spherical Mercator projection
<900913> +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 +over +nadgrids=#null +no_defs <>
How to get Circle radius in meters
May be this is existing question, but i am not getting proper result. I am trying to create Polygon in postgis with same radius & center getting from openlayers circle.
To get radius in meters I followed this.
Running example link.
var radiusInMeters = circleRadius * ol.proj.METERS_PER_UNIT['m'];
After getting center, radius (in meters) i am trying to generate Polygon(WKT) with postgis (server job) & drawing that feature in map like this.
select st_astext(st_buffer('POINT(79.25887485937808 17.036647682474722 0)'::geography, 365.70644956827164));
But both are not covering same area. Can any body please let me know where i am doing wrong.
Basically my input/output to/from Circle will be in meters only.
ol.geom.Circle might not represent a circle
OpenLayers Circle geometries are defined on the projected plane. This means that they are always circular on the map, but the area covered might not represent an actual circle on earth. The actual shape and size of the area covered by the circle will depend on the projection used.
This could be visualized by Tissot's indicatrix, which shows how circular areas on the globe are transformed when projected onto a plane. Using the projection EPSG:3857, this would look like:
The image is from OpenLayer 3's Tissot example and displays areas that all have a radius of 800 000 meters. If these circles were drawn as ol.geom.Circle with a radius of 800000 (using EPSG:3857), they would all be the same size on the map but the ones closer to the poles would represent a much smaller area of the globe.
This is true for most things with OpenLayers geometries. The radius, length or area of a geometry are all reported in the projected plane.
So if you have an ol.geom.Circle, getting the actual surface radius would depend on the projection and features location. For some projections (such as EPSG:4326), there would not be an accurate answer since the geometry might not even represent a circular area.
However, assuming you are using EPSG:3857 and not drawing extremely big circles or very close to the poles, the Circle will be a good representation of a circular area.
ol.proj.METERS_PER_UNIT
ol.proj.METERS_PER_UNIT is just a conversion table between meters and some other units. ol.proj.METERS_PER_UNIT['m'] will always return 1, since the unit 'm' is meters. EPSG:3857 uses meters as units, but as noted they are distorted towards the poles.
Solution (use after reading and understanding the above)
To get the actual on-the-ground radius of an ol.geom.Circle, you must find the distance between the center of the circle and a point on it's edge. This could be done using ol.Sphere:
var center = geometry.getCenter()
var radius = geometry.getRadius()
var edgeCoordinate = [center[0] + radius, center[1]];
var wgs84Sphere = new ol.Sphere(6378137);
var groundRadius = wgs84Sphere.haversineDistance(
ol.proj.transform(center, 'EPSG:3857', 'EPSG:4326'),
ol.proj.transform(edgeCoordinate, 'EPSG:3857', 'EPSG:4326')
);
More options
If you wish to add a geometry representing a circular area on the globe, you should consider using the method used in the Tissot example above. That is, defining a regular polygon with enough points to appear smooth. That would make it transferable between projections, and appears to be what you are doing server side. OpenLayers 3 enables this by ol.geom.Polygon.circular:
var circularPolygon = ol.geom.Polygon.circular(wgs84Sphere, center, radius, 64);
There is also ol.geom.Polygon.fromCircle, which takes an ol.geom.Circle and transforms it into a Polygon representing the same area.
My answer is a complement of the great answer by Alvin.
Imagine you want to draw a circle of a given radius (in meters) around a point feature. In my particular case, a 200m circle around a moving vehicle.
If this circle has a small diameter (< some kilometers), you can ignore earth roudness. Then, you can use the marker "Circle" in the style function of your point feature.
Here is my style function :
private pointStyle(feature: Feature, resolution: number): Array<Style> {
const viewProjection = map.getView().getProjection();
const coordsInViewProjection = (<Point>(feature.getGeometry())).getCoordinates();
const longLat = toLonLat(coordsInViewProjection, viewProjection);
const latitude_rad = longLat[1] * Math.PI / 180.;
const circle = new Style({
image: new CircleStyle({
stroke: new Stroke({color: '#7c8692'});,
radius: this._circleRadius_m / (resolution / viewProjection.getMetersPerUnit() * Math.cos(latitude_rad)),
}),
});
return [circle];
}
The trick is to scale the radius by the latitude cosine. This will "locally" disable the distortion effect we can observe in the Tissot Example.
Do my tiles need to adhere to any particular specs?
I have a large image file which I'd like to turn into a map with LeafletJS. I am going to be using the Python Imaging Library to cut it up into all the various tiles I need.
However, I can't find any information about using custom maps in Leaflet. Do I provide Leaflet with the range of X,Y,Z info somehow? Do I give it the pixel size of each tile? Does it figure this out on its own?
To put my question into one concise question: What do I need to do in order to have image files that can double as map tiles with LeafletJS, and what, if anything, do I need to do in my front-end script? (beyond the obvious specifying of my custom URL)
You are looking for a TileLayer. In this TileLayer, you give the URL for the to-be-fetched images to leaflet with a template like this:
http://{s}.somedomain.com/blabla/{z}/{x}/{y}.png
When you are at the specified zoom, x and y level, Leaflet will automatically fetch the tiles on the URL you gave.
Depending on the image you want to show, the bigger part of the work will however be in the tile generation. Tiles by default have a 256x256px size (can be changed in the TileLayer options), and if you are using geodata the used projection is Mercator projection. It may take some time to get the tile ids right. Here is an example on how the tile ids work.
You can even serve tiles directly from a database.
The format leaflet specifies is very flexible.
Leaflet just uses the z,x,y place holders to request specific tiles.
For example:
L.tileLayer('http://localhost/tileserver/tile.aspx?z={z}&x={x}&y={y}', {
minZoom: 7, maxZoom: 16,
attribution: 'My Tile Server'
}).addTo(map);
where Tiles.aspx
Option Strict On
Partial Class tile
Inherits System.Web.UI.Page
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
Dim z, x, y As Integer
z = CInt(Request.QueryString("z"))
x = CInt(Request.QueryString("x"))
y = CInt(Request.QueryString("y"))
Dim b() As Byte = DB.GetTile(z, x, y)
Response.Buffer = True
Response.Charset = ""
'Response.Cache.SetCacheability(HttpCacheability.NoCache)
Response.ContentType = "image/png"
Response.AddHeader("content-disposition", "attachment;filename=" & y & ".png")
Response.BinaryWrite(b)
Response.Flush()
Response.End()
End Sub