[Nearest Neighbor] Code and basic test for nearest neighbor by kushalpokharel · Pull Request #28 · geocaml/ocaml-rtree

kushalpokharel · 2023-10-14T19:26:30Z

I have added two functions: mindist and minmaxdistance, which will be helpful in pruning the tree while searching for the nearest neighbor. The code doesn't work yet. I have some doubts about the implementation:

Should we add the distance functions to the Value module as I have added or do we make it specific to module Point in n dimension?
If I make another module called Point with floatarray representing points in n dimensions. How do I make sure that the second parameter is of type Envelope?

AryanGodara · 2023-10-16T07:18:35Z

+  let mindist (p:floatarray) (e:envelope) = 
+    let (x0,y0,x1,y1) = Rtree.Rectangle.coords e in 
+    let gete ind = if ind==0 then x0
+                else if ind==1 then y0 else if ind==2 then x1 else y1 in


multiple if-else is not a good idea IMO
Maybe you can use a match statement here, something like this

let gete = match ind with ... | 1 -> ... |2 -> ... ...

Agree with @AryanGodara here, also note the difference between = and == in OCaml (both can be used to check for equality): https://cs3110.github.io/textbook/chapters/mut/refs.html?highlight=physical#physical-equality

AryanGodara · 2023-10-16T07:19:27Z

+
+  let minmaxdist p e = 
+    let (x0,y0,x1,y1) = Rtree.Rectangle.coords e in 
+    let gete ind = if ind==0 then x0


match here as well

Thank you @AryanGodara. I also need some feedback on how the point shall be stored?

Thank you @AryanGodara, I will change this but I also need feedback on where the point is stored in the code. @patricoferris I am waiting for the feedback

patricoferris · 2023-10-26T22:22:45Z

  (** Given a value, calculates the envelope for it. *)
+
+  val mindist: t -> envelope -> float
+  val minmaxdist: t -> envelope -> float


Do these need to be exposed in the interface?

I wanted to test these functions as well. Is that not necessary?

Now that they're a part of the Value signature then we need them here and can be tested individually. Could we add some documentation strings to them ? minmaxdist is a little opaque I think ?

patricoferris · 2023-10-26T22:23:23Z


 module R = Rtree.Make (Rtree.Rectangle) (V)

+module Vp = struct


What is Vp short for?

It is short for (Value for Point)

…envelope

kushalpokharel · 2023-10-27T10:08:42Z

Hi @patricoferris, please review the latest changes. I have listed my approach below which is based on the paper you provided.

Within the envelope, we have two functions mindist and minmaxdist which we need to provide to calculate the distance from a point to that envelope (bounding box).
The nearest neighbor function is available inside rtree which takes a rtree and a point (float list) and traverses each node and sees if the distance from the envelope of the node to the point is greater than the minmaxdist. If the distance is greater then it doesn't traverse, else it traverses that node.
I have added tests for two distance functions and one nearest_neighbor.

There might be some mistakes as I have only tested a basic case for nearest neighbor. Please guide me on how to create a deterministic large R tree to correctly test the nearest neighbor function.

kushalpokharel · 2023-10-29T07:23:16Z

@patricoferris, today is the last day for some contribution, if you could review this and hopefully we could resolve this, it would be an addition for the outreachy application

patricoferris · 2023-10-29T08:54:34Z

@harshey1103 please do still reference unmerged PRs in your application :))

patricoferris

This is a great step in the right direction @kushalpokharel. When I was thinking about the interface for this feature, I thought the distance functions would end up in the Rtree_intf.Value module? Users would then provide their own distance functions from whatever item they're storing to whatever envelope they are using? This would allow us to have a nearest neighbour function that works for all Rtree's and not just points, what do you think? Am I missing something?

patricoferris · 2023-10-29T09:01:09Z

+
+let mindist p e =
+  let x0, y0, x1, y1 = (x0 e, y0 e, x1 e, y1 e) in
+  let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in


I think these indirections are potentially a little more confusing than helpful. I think it would be clearer and more maintainable to write these in full, even if it seems a little more verbose. Seem my overview comment before making changes to this directly though.

patricoferris · 2023-10-29T09:02:01Z

+
+let minmaxdist p e =
+  let x0, y0, x1, y1 = (x0 e, y0 e, x1 e, y1 e) in
+  let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in


Similar to the previous comment.

patricoferris · 2023-10-29T09:02:51Z

+let minmaxdist p e =
+  let x0, y0, x1, y1 = (x0 e, y0 e, x1 e, y1 e) in
+  let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in
+  let rm k =


A slightly more descriptive name would be helpful here, and also so we don't confuse rm and rM.

patricoferris · 2023-10-29T09:03:33Z

+  in
+
+  let rM k =
+    if get p k >= (gete k +. gete (k + 2)) /. 2. then gete k else gete (k + 2)


The gete indirection could just be replace with direct use of the x0 etc. variables no ?

patricoferris · 2023-10-29T09:04:20Z

  val contains : t -> t -> bool
  (** [contains a b] asks whether [b] is contained by [a]. *)
+
+  val minmaxdist : float list -> t -> float


Why are these needed in envelope?

We could put this in a separate module called Point, or create a function in an envelope, to calculate the distance from a point to that envelope. This seemed easier to me. I know this is not the appropriate place for the function. Need to find its home.

kushalpokharel · 2023-10-30T04:35:13Z

This is a great step in the right direction @kushalpokharel. When I was thinking about the interface for this feature, I thought the distance functions would end up in the Rtree_intf.Value module? Users would then provide their own distance functions from whatever item they're storing to whatever envelope they are using? This would allow us to have a nearest neighbour function that works for all Rtree's and not just points, what do you think? Am I missing something?

Exactly my thought and my question in the first comment. I wanted to do the same. However, calculating distances from a value to an envelope was confusing to me. I think the users can give the distance function between two envelopes in the R-tree because we could turn the value into an envelope. Is this approach correct?

kushalpokharel · 2023-11-02T18:08:40Z

Hi @patricoferris, I made some changes to the code especially the location of distance functions inside V module. Can you review this?

Regarding other comments:

Naming is still the same, will change after the structure is set
about using x0 instead of gete, what I am actually doing is setting up the function for one axis. For example: if I was to implement distance for 3D I would just have to add gete 2. If this doesn't make sense to you, we can discuss.

kushalpokharel · 2023-11-08T05:52:32Z

Hi @patricoferris, I made some changes to the code especially the location of distance functions inside V module. Can you review this?

Regarding other comments:

Naming is still the same, will change after the structure is set

about using x0 instead of gete, what I am actually doing is setting up the function for one axis. For example: if I was to implement distance for 3D I would just have to add gete 2. If this doesn't make sense to you, we can discuss.

Hi @patricoferris, can you provide some feedback on this?

patricoferris · 2023-11-08T10:46:39Z

+  let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in
+  let rm k =
+    if get p k <= (gete k +. gete (k + 2)) /. 2. then gete k else gete (k + 2)
+  in


Was this file committed by mistake? If so can it be removed ?

patricoferris · 2023-11-08T10:47:30Z

    let y1 = Float.max arr.(1) arr.(3) in
    Rtree.Rectangle.v ~x0 ~y0 ~x1 ~y1
+
+  let mindist _a _b= 0.


Do run a dune build @fmt --auto to run the formatter as currently the CI will not like the _b= part I think

patricoferris · 2023-11-08T10:53:01Z

  (** Given a value, calculates the envelope for it. *)
+
+  val mindist: t -> envelope -> float
+  val minmaxdist: t -> envelope -> float


Now that they're a part of the Value signature then we need them here and can be tested individually. Could we add some documentation strings to them ? minmaxdist is a little opaque I think ?

patricoferris · 2023-11-08T11:39:36Z

about using x0 instead of gete, what I am actually doing is setting up the function for one axis. For example: if I was to implement distance for 3D I would just have to add gete 2. If this doesn't make sense to you, we can discuss.

I don't quite understand, don't you already use gete 2 in this 2D case ?

let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in

kushalpokharel · 2023-11-18T10:14:51Z

about using x0 instead of gete, what I am actually doing is setting up the function for one axis. For example: if I was to implement distance for 3D I would just have to add gete 2. If this doesn't make sense to you, we can discuss.

I don't quite understand, don't you already use gete 2 in this 2D case ?
let gete ind = match ind with 0 -> x0 | 1 -> y0 | 2 -> x1 | _ -> y1 in

Sorry for the late reply, I missed the notification for this. I am using gete inside of the functions like dist (in mindist).
mindist function is calculated by identifying the nearest line of the bounding box parallel to x-axis and similarly the same process is done for the lines parallel to y-axis and if we work in higher dimension, similar is done to other axes. Hence, I want to get the coordinates according to the axis that I am working on.
For example: For minimum distance from point to rectangle: I do mindist 0 +. mindist 1.
Now mindist is parametrized by i (the axis we are working on), the gete will give us the points relating to that axis.
Does this make sense to you?

kushalpokharel · 2023-11-18T10:44:38Z

@patricoferris, I have made some variable name changes and deleted the file. Please review these changes.

Add mindist and minmaxdist functions. Tests not working

dc58d40

kushalpokharel marked this pull request as draft October 14, 2023 19:26

kushalpokharel changed the title ~~Add mindist and minmaxdist functions. Tests not working~~ [Nearest Neighbor] Add mindist and minmaxdist functions. Tests not working Oct 14, 2023

AryanGodara suggested changes Oct 16, 2023

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patricoferris reviewed Oct 26, 2023

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Add nearest_neighbor function and shift distance functions inside of …

efce65a

…envelope

kushalpokharel changed the title ~~[Nearest Neighbor] Add mindist and minmaxdist functions. Tests not working~~ [Nearest Neighbor] Code and basic test for nearest neighbor Oct 27, 2023

kushalpokharel marked this pull request as ready for review October 27, 2023 10:18

patricoferris reviewed Oct 29, 2023

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Locate distance functions inside of the V module

de89e18

patricoferris reviewed Nov 8, 2023

View reviewed changes

Change variable name and code formatting

b3d6034


		module R = Rtree.Make (Rtree.Rectangle) (V)

		module Vp = struct

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kushalpokharel commented Oct 27, 2023

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