I have coordinates, which are assigned a corresponding geohash in my database. Now I want to retrieve all of the coordinates within two bounding coordinates (top right and top left corner). How can I do that properly?
I tried getting the geohash that fits both of those bounding coordinates, but this solution does not work when they are in completely different regions of the world (so they are not sharing anything in common).
Is there a better way to do that?
Thanks for your help
Unfortunately, this isn't something you can do out-of-the-box with datastore / App engine. (There are no built in spatial queries.)
For early prototyping, etc., you can do it the hard way - retrieve all the rows, and discard the ones not meeting your query in code. Obviously, probably not viable with real production data.
See related question Query for Entities Nearby with Geopt for some possible production solutions.
Related
Is there a simple/quick way to find out the dimensions of a 3D axis aligned bounding box for an item with rotations in the <x,y,z> axes? I know that in math there are different methods/equations to come up with the same answer for a problem and I've previously in the past explained with bare bones information about a method that worked for me, that I probably didn't explain well.
I also know that there are (downloadable)functions available for some languages like java and python to help solve/tackle parts of the math. Though that might not help those that want to understand those different methods better or might not have access to those particular functions for the language they are using.
So if a person has the following information:
The item center point coordinate in the x,y,z
The item x,y,z size
Along with the x,y,z rotation(s)
What would be the easiest approach with a person knowing that information, while either using or not using the item center point, matrix/matrices or cos and sin. Though an approach that would also be compact enough to take up the least amount of memory usage.
I am a beginner user of Foursquare API.
Most of the Foursquare techniques I learned so far is to do query such as search for or explore from a single location point (e.g. a café or a hotel) in a single geographical coordinate pair of longitude and latitude.
My question is, if it is possible to make an query to explore venues within an area, instead of in the vicinity of a single location point. By ‘an area’, I specifically mean the unit of the administrative division, such as a borough, of a neighbourhood.
In other words, my intending query, if possible, would start from an area specification of the administrative division of my interest (e.g. borough), such as its name or its border’s geographic coordinates—as a 'key' to link with Foursquare data, rather than start from a single location point.
I downloaded GeoJson file that already defined the geographical coordinates of the border of the administrative division of neighbourhoods in a city that I am interested in (link: http://cdn.buenosaires.gob.ar/datosabiertos/datasets/barrios/barrios.geojson). Just FYI, in this link, the neighbourhood is described as ‘barrio’ and the border is defined in the form of 'Polygon'.
I just wonder if I can use an area specification—either the name of an administrative division or a set of the geographic coordinates of an administrative division's border—as a key to make an query about venues such as restaurants, hospitals, and polices within the unit of an administrative division (e.g. borough) from corner to corner.
I guess that the underlying question is if Foursquare side has such info stored in somewhere in its system: if not, my contemplated approach would not work.
Or there might be a totally different workaround to achieve my goal.
If anyone can advise me on this matter, I would highly appreciate it.
Thanks
Given the parameters listed in the docs I think that the best approach would be to use the ll or near parameters and also include a radius so you can limit the search for a given area or region.
To get the middle point for the polygon I guess you would need to do some math but shouldn't be that difficult.
Besides this I think there doesn't seem to be any other parameter in Foursquare API to search by area or by a coordinates array (polygon).
Anyways, I would suggest that you go through the Foursquare API docs for both search and explore endpoints and check for yourself.
since you already have the polygon of interested region:
you could fit many small radius circles within to cover majority of the area.
this is not recommended as it may be rate limited or get you blacklisted but: the foursquare website has a 'draw' tool that allows you to draw a polygon and search venues within. (open networks tab under inspect in your browser and see request) I have noticed that it also can't take very complex polygons, no enclaves, and it further aggressively simplifies polygons to remove holes/dents/land bridges.
here's my demo requests. polygon search isn't strict and might show some venues outside the border.
the url:
https://foursquare.com/explore?mode=url&polygon=35.957999786220704%2C-80.41236877441406%3B35.897393965545646%2C-80.38215637207031%3B35.87847989454576%2C-80.55107116699219%3B35.954664894270834%2C-80.54901123046875%3B35.994118756097%2C-80.386962890625%3B35.957999786220704%2C-80.41236877441406
the corresponding get for venues:
https://api.foursquare.com/v2/search/recommendations?locale=en&explicit-lang=false&v=20210302&m=foursquare&limit=30&intent=bestnearby&polygon=40.8252411857252%2C-74.00630950927733%3B40.817446884558805%2C-73.99772644042969%3B40.81147063339219%2C-73.99875640869139%3B40.80757278825516%2C-74.00768280029297%3B40.80887209540822%2C-74.01729583740234%3B40.81406906961218%2C-74.02175903320312%3B40.8197852710803%2C-74.02210235595702%3B40.826280356677124%2C-74.01695251464844%3B40.8252411857252%2C-74.00630950927733&wsid={}&oauth_token={}
SITUATION
I have a database with 2,000,000 cities. All of them have coordinates of the city center and mostly all - GeoJSON boundaries. I'm trying to implement a geocoding service that would find cities that intersect with a given point using node.js, mongodb, redis, memcached (and golang, if that is necessary, cause I'm just totally new to it )
PROBLEM
I know how to work with points (lat and lng) since both MongoDB and Redis support geoindexes but I've never seen anything about polygons.
I guess MongoDB won't really help cause of its speed (since it work on disks), but any memory database should deal with this problem. The thing is I can't even think of any way to implement it.
I'll be happy if someone point me how to make it. Thanks.
You may implement a point-in-polygon algorithm yourself. I've done something similar on https://api.3geonames.org
First do a bounding box to identify candidate polygons, then run a PIP. https://en.wikipedia.org/wiki/Point_in_polygon
geo.lua (https://github.com/RedisLabs/geo.lua) works with the requirements you have here but it's not very performant (not sure what has changed since last i checked).
I'm using the Overpass API to query Open Street Maps for nearby road segments. I am pretty sure that my query is returning all of the nodes of the nearby way... but I only want nearby nodes of the nearby way.
In the documentation it references this problem:
In general, you will be rather interested in complete data than just
elements of a single type. First, there are several valid definitions
of what "complete map data" means. The first unclear topic is what to
do with nodes outside the bounding box which are members of ways that
lie partly inside the bounding box.
The same question repeats for relations. If you wait for a turn
restriction, you may prefer to get all elements of the relation
included. If your bounding box hits for example the border of Russia,
you likely don't want to download ten thousands kilometers of boundary
around half the world.
But I looked at the subsequent examples and didn't see the solution.
Basically, in their example, how would I restrict the elements returned to those strictly in the bounding box (rather than returning the whole boundary of Russia)?
My current query is
way (around:100,50.746,7.154) [highway~"^(secondary|tertiary)$"];
>;
out ids geom;
I'm thinking maybe I need to change it to node (around:...) and then recurse upwards to the way to query for the highway tag but I'm not sure if I am even on the right track.
Actually, it's even a bit more complicated, as you need the set intersection of all nodes in a 100m distance and those nodes belonging to one of the relevant ways. Here's how your query should look like: Adjust distance, tags for ways as needed.
Note that depending on the tagging, there's no guarantee that you will find a node in a certain distance, especially if roads tend to be rather straight and longish. This for sure will impact your results, so a bit experimenting with a suitable radius is probably needed.
// Find nodes up to 100m around center point
// (center is overpass turbo specific for center point lat/lon in current map view)
node(around:100,{{center}})->.aroundnodes;
// recurse up to ways with highway = secondary/tertiary
way(bn.aroundnodes)[highway~"^(secondary|tertiary)$"]->.allways;
// determine nodes belonging to found ways
node(w.allways)->.waynodes;
(
// determine intersection of all ways' nodes and nodes around center point
node.waynodes.aroundnodes;
// and return ways (intersection is just a workaround for a bug)
way.allways.allways;
);
out;
check it out in overpass turbo: http://overpass-turbo.eu/s/hPV
What's the best way to determine if a point is within a certain distance of a GEOJSON polygon? Should one use TurfJS buffer method (https://github.com/Turfjs/turf-buffer#turf-buffer)? Can one perform queries on the buffered polygon?
It's clear to me one could us the TurfJS' inside method (https://github.com/Turfjs/turf-inside) to determine whether a point is within a polygon. I'm just curious what the best approach would be for finding whether or not a point is inside of a buffered polygon.
For example:
I have a number of neighborhoods provided as a GEOJSON polygon files. I also have a set of locations/addresses for employees (already geocoded to lat/long coordinates). What would be the best way to see whether or not my employees live within 10 miles of a given neighborhood polygon?
Thanks!
Yes, you can use buffer in conjunction with inside to find points within 10 miles of something else, eg, expanding on the existing examples,
var pt = point(14.616599, -90.548630)
var unit = 'miles'
var buffered = buffer(pt, 10, unit)
var ptTest = point(-1, 52)
var bIn = inside (ptIn, buffer)
which should obviously be false.
In general, though, buffering is somewhat expensive, so you would not necessarily want to do this every time you run the query. There are a couple of things you can do to speed things up:
1). Pre-buffer your search areas
2). Use some kind of R-tree type index, which will first check bounding box intersection, and avoid lots of unecessary point in polygon operations. turfjs, which I hadn't heard of until seeing your post, uses jsts under the hood for a number of operations, including buffering. This library has an implemention of R-tree indexes that you could potentially use. Here is a fun example of this being done.
In general, in situations where you have a spatial (R-tree type) index in place, such as a spatially enabled database like Postgis on top of Postgres, you would use an operator like ST_Dwithin (geom1, geom2, distance) in a where clause to find all points within some distance of another geometry, and this would be very efficient as many candidates would be rejected for failing an initial bounding box test.
Really, it depends on the size of your data and frequency of queries. There is nothing, in principle, wrong with doing contains queries on a buffer. I hope I haven't created more questions than answers.
I'm using GeoScript to do that sort of calculations in JavaScript. It has a distance method in the geom.Geometry class which can return the minimum distance between two geometries. You could use that, or take a look at the source on GitHub to see how they do it if you want to roll your own solution.