Create getZoomFromCoordinates function

[nstjean]

From @sagarpreet-chadha in https://github.com/publiclab/plots2/issues/6946:

Now for the existing users who do not have zoom:xx tags yet,

We need to implement a function in LBL getZoomFromCoordinates(lat, lng) -> This function takes lat and lng as input and returns a zoom level. To implement this you need to change LBL API to take an array as input of format - More details here: https://github.com/publiclab/leaflet-blurred-location-display#zoom_filter--changing-the-zoom-levels-range-where-x-precision-marker-should-be-visible- If this array is not passed we can use default array : zoom_filter = [[0,4,0] , [5,7,2] , [8,11,4] , [12,18,5]] ; Using this zoom_filter array, the getZoomFromCoordinates will return zoom level. So in plots2 now, if zoom:xx is not present we will call this function.

[nstjean]

I will be working on this :smile:

[sagarpreet-chadha]

Awesome!!! Thank you :)

[nstjean]

@sagarpreet-chadha just want to clarify. How does the zoom_filter array calculate and return a zoom level? Does it exist anywhere already or is it something brand new?

[sagarpreet-chadha]

Yes it has already be done in LBLD (https://github.com/publiclab/leaflet-blurred-location-display)! Implementation wise would be same but the _meaning of zoomfilter would be little different.

Check more about zoom_filter array here: https://github.com/publiclab/leaflet-blurred-location-display#zoom_filter--changing-the-zoom-levels-range-where-x-precision-marker-should-be-visible-

Briefly: Let zoom_filter = [[0,4,0] , [5,7,2] , [8,11,4] , [12,18,5]] ; Each array corresponds to [lower precision level , upper precision level , zoom level to set]. So for example: [5,7,2] means if the precision of lat/lng is >=5 (lat = 23.12345 , lng = 78.32123) and <=7 then we should set zoom = 2.

Here is how it is implemented in LBLD : https://github.com/publiclab/leaflet-blurred-location-display/blob/b46195a8b407ed55cf41801a5c4fe6f3085d61fa/src/blurredLocationDisplay.js#L23

We take zoom_filter as input when we initaiize LBLD object: https://github.com/publiclab/leaflet-blurred-location-display/blob/b46195a8b407ed55cf41801a5c4fe6f3085d61fa/examples/index.html#L103

Makes sense? Thanks!

[nstjean]

Ahhhh! Ok, I see now! So that function returns whether or not a marker should be visible at the current zoom level. But in our new function we want to check the filters to find which zoom level to return. Yes?

[nstjean]

@sagarpreet-chadha I understand your explanation, however when I look at the code it doesn't seem to be doing what you describe. Say we are looking at [0,4,0]... this should correspond to a precision level between 0 and 4 equals a zoom of 0.

if(current_zoom >= options.zoom_filter[i][0] && current_zoom <= options.zoom_filter[i][1])
...
          if(precision >= options.zoom_filter[i][2]){
            return true ;
          }

This is checking if the zoom level is between is between 0 and 4, and then comparing the precision to 0.

[nstjean]

Currently on LBL exammples/index.html when I look at the map zoom levels and precision it is showing on the screen I get the following: Precision -1 : (rounded to nearest 10s) -- Zoom level 1, 2, 3, 4, 5 Precision 0 : Zoom 6, 7, 8, 9 Precision 1 : Zoom 10, 11, 12 Precision 2 : Zoom 13, 14, 15 Precision 3 : Zoom 16, 17, 18

[sagarpreet-chadha]

Yes that function is coded in context of LBLD (which marker should be visible according to zoom). For LBL we need different yet similar implementation. Makes sense? Thanks!

[nstjean]

Then here in this file is this code, which matches what I was seeing on the screen. https://github.com/publiclab/leaflet-blurred-location/blob/1040824864a3e05a83e1e3d9ac75626d56a01ae6/src/blurredLocation.js#L204-L207

[nstjean]

Ahhh, ok. :) I'll just use the precisionTable then, since it's already in use and is the same concept... but with converting precision to zoom we don't need a range, it's just 1 to 1.

[sagarpreet-chadha]

Yes okay we can do 1:1, but we need to also allow people to add their 1:1 mapping array as input to API. Thanks!

[nstjean]

Ahh, ok. Yes. Is the format of precisionTable above acceptable or should it be an array of arrays like this? var precisionTable = [[-2, 2], [-1, 3], [0, 6], [1, 10], [2, 13], [3, 16]]

[sagarpreet-chadha]

I think it is more easy to understand if we do it as we have done in LBLD. [x, y, z] For x <= precision <= y, zoom should be z. What do you think? Thanks!

On Wed, 18 Dec 2019, 00:39 Natalie St Jean, notifications@github.com wrote:

Ahh, ok. Yes. Is the format of precisionTable above acceptable or should it be an array of arrays like this? var precisionTable = [[-2, 2], [-1, 3], [0, 6], [1, 10], [2, 13], [3, 16]]

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[nstjean]

That's fine, but it will be the same on all of them... because precision is a single number, not a range. var precisionTable = [[-2, -2, 2], [-1, -1, 3], [0, 0, 6], [1, 1, 10], [2, 2, 13], [3, 3, 16]]

We could do precision, then a range of zooms? var precisionTable = [[-2, 1, 2], [-1, 3, 5], [0, 6, 9], [1, 10, 12], [2, 13, 15], [3, 16, 18]]

Or honestly for consistency's sake we could keep it in the exact same order as in LBLD. Min zoom -> max zoom -> precision. That might be the best option. var precisionTable = [[1, 2, -2], [3, 5, -1], [6, 9, 0], [10, 12, 1], [13, 15 , 2], [16, 18, 3]]

[sagarpreet-chadha]

Hey @nstjean , sorry for not able to clear this. This function should return zoom, right? Why do you think there is 1:1 mapping between precision and zoom? Why we can not have multiple precisions mapped to 1 zoom level?

Example: if precision is in between [2,5] then this function should return lets say zoom level 8. Makes sense?

@jywarren can you chime in here? Thanks!

[nstjean]

Because based on the code there is a range of zooms for each precision level. There is only precision levels -2 through 3. The zoom levels are 1 through 18.

[nstjean]

This is what shows on the map itself when it's in use... Precision level -2 isn't even used.

Currently on LBL exammples/index.html when I look at the map zoom levels and precision it is showing on the screen I get the following: Precision -1 : (rounded to nearest 10s) -- Zoom level 1, 2, 3, 4, 5 Precision 0 : Zoom 6, 7, 8, 9 Precision 1 : Zoom 10, 11, 12 Precision 2 : Zoom 13, 14, 15 Precision 3 : Zoom 16, 17, 18

[nstjean]

I've pushed what I have complete #224 - and it works as-is. I suggest we merge this so that I can continue working in plots2 using this function, and then later if we want to change the format of the object/array I can do another PR with the change.