What should i send GET or POST if field calculating based on query params?

I have resource /api/v1/serviced-objects/ and when i send regular GET request, i get server response and each element in it contains distance field which has null value.

{
  "count": 2,
  "next": null,
  "previous": null,
  "results": [
    {
      "id": 1,
      "point": "0,30",
      "distance": null
    },
    {
      "id": 2,
      "point": "30,0",
      "distance": null
    }
  ]
}

Also i have query param user_point. If i send GET request like /api/v1/serviced-objects/?user_point=0,0, i'll get calculated value for distance field between given user_point and serviced object point in meters.

{
  "count": 2,
  "next": null,
  "previous": null,
  "results": [
    {
      "id": 1,
      "point": "0,30",
      "distance": 2000
    },
    {
      "id": 2,
      "point": "30,0",
      "distance": 1000
    }
  ]
}

So general question is - Is it still idempotent or it's better to use POST in this case?

How you choose between using a GET request with query parameters or a POST request relies on how you think about the process of calculating and updating the distance field in your application's context. Using the GET request is acceptable if the action primarily involves retrieving resources. A POST request on the other hand, would be more appropriate if it's about creating or modifying a resource.

In the given example, the inclusion of the user_point parameter and distance field calculation does not affect the idempotency of the GET request because more probably no data is being modified on the server and it is simply retrieving information based on the provided parameter. While the response may differ based on the user_point parameter, requests with the same user_point value should always produce the same response.

The short answer is till the time you are not modifying any resource value in your system you should go for the GET request, otherwise POST