Convert keypoints to point2f to store in a file or localstorage

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1

Hi! :slight_smile:
according to the documentation, its possible to convert an KeyPoint into a point2f…

Well im trying to convert an array of keyPoints from cvOrb.

let orb = new cv.ORB();
    orb.setMaxFeatures(MAX_FEATURES);

    cv.cvtColor(object.im, object.gray, cv.COLOR_RGBA2GRAY, 0);
    orb.detectAndCompute(object.gray, new cv.Mat(), object.kp, object.descriptors);

    let t = new cv.Mat();
    object.kp.convertTo(t, )

basically i want to known how-to convert in javascript! :slight_smile:

https://docs.opencv.org/4.5.3/d2/d29/classcv_1_1KeyPoint.html#acfcc8e0dd1a634a7583686e18d372237

other alternative would be to use filestorage to store the keypoints as yaml

https://answers.opencv.org/question/4040/to-save-vector-keypoint-to-file-using-builtin-write-function/

I didn’t find any example, and try to check the bindings and source code, but didn’t get far. is this even possible? thanks.

2

may i ask, why you want to do this ?
what do you plan to do with the point locations ?
(you’d basically make a loop and extract the pt member from each keypoint)

then, you’re usually not allowed to access the file system from js,
and it’s the same here - no FileStorage

3

well, i want to do this, because i need to load 40 images everytime i start this app… and it takes time to generate all the keypoints needed. then i could boost the load of the app :slight_smile:
instead of needing to load all the images, i could just load a file with keypoints, and the features matrix.

4

well, the matching uses descriptors only , so it’s far more imprtant to save those

last, this sounds, like you ty to match a query image to a “gallery” – what is the purpose of it ? if it’s “finding similar images”, you’re probably on the wrong bus, the matching process here is the wrong approach for that (lookup “BagOfWords” then)

5

are you sure? In here the ORB detectAndCompute is using the keypoints.

this.matcher.orb.detectAndCompute(this.scene.gray, new cv.Mat(), this.scene.kp, this.scene.descriptors);

Anyway I am more focus on just solving on how-to store the keypoints, not on how to detect Images. because that has been debated before and we are happy ORB for our purpose. Anyway i didn’t understand what is your suggestion about that. can you make it more clear? :slight_smile: thanks

6

it is calculating keypoints here, not using presupplied ones

finally tell us, what that is. (i think, i asked 2 times already …)

7

you are absolutely correct! thanks :slight_smile:

sorry i didnt explain. so we have a collection of many images that need to be detect using a camera in the real world. When an image is detected the app will redirect the person to a specific url, image, sound, video, or even an AR mode using jsartoolkit5 :wink:

8

do you have an example of an “image that needs to be detected” and another “using a camera in the real world.” one ?

do you have any code proving your idea works ? how would you measure “similarity” here ?

9

I released this code (the example is not working yet):

So similarity is measured in here:

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10

nice, that you could finish this (without any docs or tuts !)
we now also have a working js example for feature matching here, good !
(ppl will come for this !)

as long as ALL your images come from the (same) camera, it might even give meaningful matching results (just DONT add a feature, where users can upload their own images, then it’ll break, comparing apples to pears)

11

im finishing up an example on how-to to use it :slight_smile:
what do you mean from the same camera? it works with many different setups. lemme finish this example :slight_smile:
I used many tutorials, and different stuff. opencv is cool!

12

its working now :slight_smile: you can test it here:
https://albjeremias.github.io/trigger-cv/example/index.htm

So what i want to do is to store the object descriptors in the local storage of the browser or as a file (generated previously)

I wonder if generating it previously bring problems, but i will make some tests. the issue is that i use the videoWidth to calculate the descriptors, but it seems a bit irrelevant, since the image size changes on the camera image too…

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