I'm creating a hyper local delivery service app . I can only receive order if there is a store within 5 km radius from the user . I stored the store locations in geojson format . Is there a function in h3-js which will take radius , array of stores , h3 index and then give back the list of stores which are within 5 km range from the given h3 index . or how can i implement this using h3-js?
There are a few different parts here:
Pick a resolution: Pick an H3 resolution for lookup. Finer res means more accuracy but more memory usage. Res 8 is roughly a few city blocks in size.
Indexing Data: To use H3 for the radius lookup, you need to index the stores by H3 index. If you want this to be efficient, you'd be better off indexing all the stores ahead of time. How you do this is up to you; one easy way in JS might be to create a map of id arrays:
const lookupIndexes = stores.features.reduce((map, feature) => {
const [lon, lat] = feature.geometry.coordinates;
const h3Index = h3.geoToH3(lat, lon, res);
if (!map[h3Index]) map[h3Index] = [];
map[h3Index].push(feature.id);
return map;
}, {})
Perform the lookup: To search, index your search location and get all the H3 indexes within some radius. You can use the h3.edgeLength function to get the approximate radius of a cell at your current resolution.
const origin = h3.geoToH3(searchLocation.lat, searchLocation.lon, res);
const radius = kmToRadius(searchRadiusKm, res);
// Find all the H3 indexes to search
const lookupIndexes = h3.kRing(origin, radius);
// Find all points of interest in those indexes
const results = lookupIndexes.reduce(
(output, h3Index) => [...output, ...(lookupMap[h3Index] || [])],
[]);
See a working example on Observable
Caveats: This is not a true radius search. The k-ring is a roughly hexagonal shape centered on the origin. This is good enough for many use cases, and much faster than a traditional Haversine radius search, especially if you have many rows to search over. But if you care about the exact distance H3 might not be appropriate (or, in some cases, H3 might be fine, but you might want the indexes inside a "true" circle - one option here is to convert your circle to a close-to-circular polygon, then get the indexes via h3.polyfill).
Related
I want to do text detection in an image using only tensorfow.js or opencv.js, i have already build a EAST model on keras and converted to tensorflowjs model
can anyone help me with this, any resource will be great
Thanks.
So, initially you need to download the East frozen model and then conver it to tensorflow.js model by using the below command
tensorflowjs_converter --input_format=tf_frozen_model --output_node_names='feature_fusion/Conv_7/Sigmoid,feature_fusion/concat_3' /path_to_model /path_to_where_you_want_save_converted_model.
Next after taking an input image and loading the model the below code will detect the text is there or not
$("#predict-button").click(async function () {
let image = $("#selected-image").get(0);
let tensor = tf.browser.fromPixels(image)
.resizeNearestNeighbor([640, 320])
.expandDims(0);
tensor = tf.cast(tensor, 'float32')
const [output1, output2] = await model.predict(tensor);
const data1 = await output1.data();
const data2 = await output2.data();
As the east model gives two outputs i.e. scores and geometry. so here data1 will give the geometry (which I ignored because my end goal was to detect if the text is present not to localize it) and data2 will give the scores.
Next, I put a threshold of 0.5 to differentiate between the text is present or not. if the probability is greater than 0.5 then the text is present and if less than 0.5 than the text is not present on text.
Note: for now, I have skipped the preprocessing step (except resize) where they subtract the mean RGB value from an RGB value of input image.
I have an NSManagedObject class that's persisted in a SQLite database in Core Data. This object has persistent Latitude and Longitude properties. I'm trying to create an NSFetchedRequestController that fetches all of the instances of that class that are within a certain distance from the user. Having done some research, it seems impossible to do this with Core Data, because Core Data only supports bounding-box style queries, not predicates with blocks.
For example, I have a class of Groups with latitude and longitude properties. Given the latitude and longitude (of, say, a user), fetch all groups that are within a 6 mile radius of the given latitude and longitude.
class Group{
var latitude: Float
var longitude: Float
}
I'd like to take advantage of Core Data's R-Tree Indexing to do a fast bounding-box query on the latitudes and longitudes of instances of my class near my user. Then I'd like to filter the results with a more precise predicate, using my own block of code to see which of the instances are within my users current location. Here's the "Bounding box" query.
let request: NSFetchRequest<Group> = Group.fetchRequest()
let (topLeft,bottomRight) = boundingBox(center: center, radius: searchRadius)
let maxLat = topLeft.latitude
let minLon = topLeft.longitude
let minLat = bottomRight.latitude
let maxLon = bottomRight.longitude
let predicate = NSPredicate(format: "(%f < longitude AND longitude < %f) AND (%f < latitude AND latitude < %f)", minLon, maxLon, minLat, maxLat)
request.predicate = predicate
The problem is that I'd like a fetch that looked like this:
let location: CLLocation = /* Initialize a CLLocation */
let predicate = NSPredicate { (obj, _) -> Bool in
let object = obj as! Group
let objLocation = CLLocation(latitude: Double(object.latitude), longitude: Double(object.longitude))
return location.distance(from: objLocation) < 9656 //6 miles in meters
}
NSFetched results controller doesn't allow predicate with block. There's a significant difference between these two fetches. The first gets all groups in a Bounding Box, (the minLat, minLon, maxLat, and maxLat), the latter gets all groups in a Circle of a given radius.
I want to then use an NSFetchedRequestController to display the results in a table, and take advantage of the nice auto-update features. But of course, Core Data only supports bounding-box style queries, not the two-step filter method I need. Is there a proper solution?
I'm open to using other databases, if Core Data simply won't work with this type of use. I took a look at YapDatabase, and it seems more flexible, and includes R-Tree indexing, but I'm concerned that it's not well supported. Realm doesn't support R-Tree Indexing.
I am new to AzureMap with limited knowledge of JavaScript and looking help in getting the real time alert based on some random flag during the fleet movement based on the co ordinates .
I tried multiple sources to design it like followed Sample code enter link description here
My requirement is :
Pip should pop up or appear only on arrival of the fleet (truck) .
Thanks
To verify, when the truck gets to the end of the line you want to open a popup. I'm assuming you have a constant flow of data updating the truck position and that you can easily grab the trucks coordinate. As such you would only need a function to determine if the truck coordinate is at the end of the route line. You will likely need to account for a margin of error (i.e. within 15 meters of the end of the line) as a single coordinate can represent a single molecule with enough decimal places and GPS devices typically have an accuracy of +/- 15 meters. With this in mind all you would need to do is calculate the distance from the truck coordinate to the last coordinate of the route line. For example:
var lastRouteCoord = [-110, 45];
var truckCoord = [-110.0001, 45.0001];
var minDistance = 15;
//Get the distance between the coordinates (by default this function returns a distance in meters).
var distance = atlas.math.getDistanceTo(lastRouteCoord, truckCoord);
if(distance <= minDistance){
//Open popup.
//Examples: https://azuremapscodesamples.azurewebsites.net/index.html#Popups
}
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.
I have a model in angularJS which is bound to firebase $scope.items=$firebase(blah) and I use ng-repeat to iterate through the items.
Every item in firebase has a corresponding geofire location by the key of the item.
How can I update my controller to only include items by a custom radius around the user? I don't want to filter by distance in angular, just ask firebase to only retrieve closer items (say 0.3km around a location). I looked around geoqueries but they have a different purpose and I don't know how to bind them to the model anyway. The user may change the radius and the items list should be updated accordingly, so they need to be bound somehow.
Any suggestion is welcome, but an example would be greatly appreciated as I don't have fluency in this trio of angular/firebase/geofire yet :P
It's difficult to figure out what you need to do without seeing your code. But in general you'll need to query a Firebase ref that contains the Geohash as either the name of the child or the priority.
A good example of such a data structure can be found here: https://publicdata-transit.firebaseio.com/_geofire/i
i
9mgzcy8ewt:lametro:8637: true
9mgzgvu3hf:lametro:11027: true
9mgzuq55cc:lametro:11003: true
9mue7smpb9:nctd:51117: true
...
l
...
lametro:11027
0: 33.737797
1: -118.294708
actransit:1006
actransit:1011
actransit:1012
...
The actual transit verhicles are under the l node. Each of them has an array contains the location of that vehicle as a longitutude and latitude pair.
The i node is an index that maps each vehicle to a Geohash. You can see that the name of each node is built up as <geohash>:<metroarea>:<vehicleid>.
Since the Geohash is at the start of the name, we can filter on Geohash with a Query:
var ref = new Firebase("https://publicdata-transit.firebaseio.com/_geofire");
var query = ref.child('i').startAt(null, '9mgzgvu3ha').endAt(null, '9mgzgvu3hz');
query.once('child_added', function(snapshot) { console.log(snapshot.name()); });
With this query Firebase will give us all nodes whose name falls within the range. If all is well, this will output the name of one node:
9mgzgvu3hf:lametro:11027
Once you have that node, you can parse the name to extract the vehicleid and then lookup the actual location of the vehicle under l.
Calculating Geohashes based on a location and a range
In the snippet above, I hardcoded the geohash values to use. Normally you'll want to to get all nodes in a certain range around a center. Instead of calculating these yourself, I recommend using the geohashQueries function from GeoFire for that:
var whitehouse = [38.8977, -77.0366];
var rangeInKm = 0.3;
var hashes = geohashQueries(center, radiusInKm*1000);
console.log(JSON.stringify(hashes));
This outputs a number of Geohash ranges:
[["dqcjqch","dqcjqc~"],["dqcjr10","dqcjr1h"],["dqcjqbh","dqcjqb~"],["dqcjr00","dqcjr0h"]]
You can pass each of these Geohash ranges into a Firebase query:
hashes.forEach(function(hash) {
var query = geoFireRef.child('i').startAt(null, hash[0]).endAt(null, hash[1]);
query.once('child_added', function(snapshot) { log(snapshot.name()); });
});
I hope this helps you settings things up.
Here is a Fiddle that I created a while ago to experiment with this stuff: http://jsfiddle.net/aF9mN/.