Calculate distance between two PFGeopoints in a NSPredicate for a Parse Query - objective-c

Question

I have a special case when I want to do something like
let predicate = NSPredicate(format:"
DISTANCE(\(UserLocation),photoLocation) <= visibleRadius AND
DISTANCE(\(UserLocation),photoLocation" <= 10)"
var query = PFQuery(className:"Photo", predicate:predicate)
Basically, I want to get all photos that are taken within 10km around my current location if my current location is also within the photo's visible radius
Also, photoLocation and visibleRadius are two columns in the database, I will supply UserLocation as a PFGeoPoint.
Is it possible to achieve this? In my opinion, I don't think that I may call, for example, photoLocation.latitude to get a specific coordinate value. May I?
I'll appreciate you a lot if this can be achieved!!

Answer 1

I found this at the pares.com docs here is the link
let swOfSF = PFGeoPoint(latitude:37.708813, longitude:-122.526398)
let neOfSF = PFGeoPoint(latitude:37.822802, longitude:-122.373962)
var query = PFQuery(className:"PizzaPlaceObject")
query.whereKey("location", withinGeoBoxFromSouthwest:swOfSF, toNortheast:neOfSF)
var pizzaPlacesInSF = query.findObjects()
This code fetch you all the objects that are in a rectangle area defined by the swOfSF & neOfSF objectc, where seOfSF is in the south-west corner and neOfSF is in the north-east corner.
You can make some alterations to the code and get all the objects in rectangle area that your object is in middle
i would recommend that you don't use a radius, because it will take a lot of calculations. Instead use a rectangle area (like in the code i gave you).
just calculate what is the max/min longitude & max/min latitude from your position and fetch all the objects that are in between. you can read about how to fine the min/max longitude & latitude here Link

Answer 2

I managed to solve it using Parse Cloud Code, here is the quick tutorial
Parse.Cloud.define("latestPosts", function(request, response) {
var limit = 20;
var query = new Parse.Query("Post");
var userLocation = request.params.userLocation;
var searchScope = request.params.searchScope;
var afterDate = request.params.afterDate;
var senderUserName = request.params.senderUserName;
query.withinKilometers("Location", userLocation, searchScope);
query.greaterThan("createdAt", afterDate);
query.notEqualTo("senderUserName",senderUserName);
query.ascending("createdAt");
query.find({
success: function(results) {
var finalResults = results.filter(function(el) {
var visibleRadius = el.get("VisibleRadius");
var postLocation = el.get("Location");
return postLocation.kilometersTo(userLocation) <= visibleRadius;
});
if (finalResults.length > limit) {
var slicedFinalResults = results.slice(0, 20);
response.success(slicedFinalResults);
} else {
response.success(finalResults);
}
},
error: function() {
response.error("no new post");
}
});
});
The code above illustrate a basic example of how to use Cloud Code. Except, I have to make sure that all the returned image are in the union of user's search scope and photo's visible circle. There are more techniques such as Promises. But for my purpose, the code above should just suffice.