Layers and summarized positions

What is a layer

A layer have a layer-id and a layer name + some explanations (possibly)
All processing is done within layer
One tracker are always connected to a Layer
User might create layers
for no only two layers, real and simulated drones
All layers are selectable on map page

Position calculation

A layer contain a list of positions for each zoom level
For all some levels less that 18, position are a sum of all tracker within a certain area
A map on a certain zoom level have a grid, for ex 100 X 100 squares for summarize all drones in each square into on position

Zoom level calculation

Zoom Longitude = ROUND( LONGITUDE / ( 360 / ( 2 ^^(ZOOMLEVEL-1) ) ) , 1) * 10
Zoom Latitude = ROUND( LATITUDE / ( 180 / ( 2 ^^(ZOOMLEVEL-1) ) ) , 1) * 10

Solution to zoom level calculation

For each zoom level we calculate position lists longitude and latitude, containing the calculated Zoom Longitude and Zoom Latitude positions from each tracker position.
If more than one tracker present in a certain positions, we increment a counter number_of_trackers
When ask for positions on a certain zoom level, we use this lists to retrieve a positions, instead of direct tracker positions
Each tracker level has its own set of calculated position between zoom level 1 and zoom level 17

Code implementation

class ZoomLayerServiceImpl contain and calculate posistion for one zoomlevel
class TrackerLayer contain a list of 15 ZoomLayerServiceImpl objects, one for each calculating zoom level.
Test class ZoomLayerTest

debate 2015.04.22

good morning
[11:17:25] Thai Huynh: Good morning
[11:17:52] Duong Thanh Huy: morning
[11:18:09] Leif H. Auke: all vell?
[11:18:29] Duong Thanh Huy: I think so
[11:18:31] Duong Thanh Huy: :)
[11:18:32] Duong Thanh Huy: how about you
[11:18:43] Leif H. Auke: fine to
[11:18:57] Leif H. Auke: Do you have 2 minutes for discussion?
[11:19:05] Duong Thanh Huy: sure thing
[11:19:05] Duong Thanh Huy: :)
[11:19:13] Thai Huynh: I am fine :)
[11:19:16] Thai Huynh: yes
[11:20:06] Leif H. Auke: I figures out a function for recalculate postions on different zoom levels so we dont have to show every tracker postions, but instread use summarized positions.
[11:20:28 | Redigert 11:20:57] Leif H. Auke: Could you have al look and see if this is understandable according to description
[11:20:31] Leif H. Auke: ??
[11:20:39] Leif H. Auke: https://wiki.cantara.no/display/drone/Layers+and+summarized+positions
[11:20:42] Duong Thanh Huy: ok can you give us
[11:23:38] Leif H. Auke: (its on wiki page)
[11:23:39] Duong Thanh Huy: ok
[11:23:41] Duong Thanh Huy: just had a look
[11:24:14] Leif H. Auke: got the idea ?
[11:24:55] Duong Thanh Huy: not really, sorry
[11:25:02] Leif H. Auke: you might see from the attached excel sheet how it calculate
[11:25:16] Leif H. Auke: I explain
[11:26:12] Leif H. Auke: case: If there are 10.000 drone spread out of the world and you show map on zoom level 1, you will only show maximum 10 X 10 posistions
[11:26:41] Leif H. Auke: each postition on map contain a numer of trackers included
[11:26:46] Leif H. Auke: follow...
[11:26:47] Leif H. Auke: ?
[11:26:55] Duong Thanh Huy: ok, please go on
[11:27:06] Leif H. Auke: can you open the excel sheet ?
[11:27:10] Duong Thanh Huy: I did
[11:27:37] Leif H. Auke: ok, look for ex zoom level 10
[11:28:31] Leif H. Auke: this give for longitude -2560 to 2560 decree sectors around the world
[11:28:41] Leif H. Auke: and same for longitude
[11:29:35] Leif H. Auke: that means there are 5120 X 5120 possible positions to show globally on this zoom level.
[11:29:42] Leif H. Auke: (using this calculation)
[11:30:22] Duong Thanh Huy: ok, understood
[11:31:17] Leif H. Auke: the shown size og a map on this zoom is one of 512 x 512 possible areas around the globe
[11:31:55 | Redigert 11:32:26] Leif H. Auke: this means, we only retrive a max og 100 positions on any viewed area on this zoom level.
[11:32:03] Leif H. Auke: got the Idea?
[11:32:49] Duong Thanh Huy: got it
[11:32:54] Leif H. Auke: (cool)
[11:33:10] Duong Thanh Huy: so that's the view calculation we could do
[11:34:13] Leif H. Auke: so, when we calculate positions for a tracker level, we simply precalcuate a list of postions for each zoom level beforehand (zoom 1 to 17)
[11:34:40] Leif H. Auke: and use this lists to retrive postions, reather that the basice tracker list.
[11:35:13] Leif H. Auke: UI stays the same, it simply get a diffrente postions list for each zoom level.
[11:35:25] Duong Thanh Huy: Each tracker level has its own set of calculated position between zoom level 1 and zoom level 17
[11:35:34] Leif H. Auke: yepp
[11:35:36] Duong Thanh Huy: this would mean we have to calculate a lot
[11:35:52] Duong Thanh Huy: and store such data is very costly for memory
[11:36:46 | Redigert 11:37:57] Leif H. Auke: My quess is, its 17 x 2 calculation for each tracker each time using this spcesial function. I think its pretty fast.
[11:37:16] Leif H. Auke: The list will not be to big, because there are not that many areas covered
[11:37:31] Leif H. Auke: I like to try?
[11:38:12] Duong Thanh Huy: it's ok, but I think we will run into performance issues.
[11:38:34] Leif H. Auke: hmm
[11:38:50] Duong Thanh Huy: for examples: you have 10000 drones
[11:38:55] Leif H. Auke: java in memory on a modern computer are suprisingly fast
[11:40:00] Duong Thanh Huy: then you have to store 18 levels, thatn means 10000 x 18 objects
[11:41:05] Leif H. Auke: you dont store one object pr. tracker. You store one object pr. calulated position
[11:41:24] Leif H. Auke: it means on zoom 1, maximun 10 X 10 = 100 entries
[11:41:28] Leif H. Auke: and so on....
[11:41:52] Leif H. Auke: imagine speed ->
[11:42:38] Leif H. Auke: a cpu with 2 GHZ clock, spending for ex 100.000 cycles pr. calculation do 20.000 calculations a second
[11:43:20] Leif H. Auke: if is use 10.000 cycles, it will be 200.000 calculations a second. (CPU's are stubidetly fast)
[11:43:25] Leif H. Auke: ;)
[11:43:42] Duong Thanh Huy: ok
[11:43:44] Duong Thanh Huy: :)
[11:43:51] Leif H. Auke: lets try?
[11:44:13] Duong Thanh Huy: ok... I'm still a little bit hesitate
[11:45:21] Leif H. Auke: alternativly the UI work harder to retrive 1000 tracker positions when showing world map (in case 1000 active trackers)
[11:45:50] Leif H. Auke: 1000 postions each 10 second X 100 users is also som network load.
[11:46:35] Leif H. Auke: a computer 1000 times faster than the network, so everything you can calculate to reduse network traffic is very good for scaling.
[11:46:39] Leif H. Auke: (its a fact)
[11:46:40] Leif H. Auke: :)
[11:47:39 | Redigert 11:47:47] Leif H. Auke: it cheaper add CPU capaseties than networking capaseties.
[11:48:28] Duong Thanh Huy: will there any changes in data structure? now we're showing a list of trackers every call
[11:49:05] Leif H. Auke: let me see....
[11:49:12] Duong Thanh Huy: how often we will recalculate for tracker layer, 10 seconds?
[11:49:52 | Redigert 11:49:57] Thai Huynh: maybe make set timer  in java code ?
[11:50:01] Leif H. Auke: we try every 10 second but actually we migh differ on different zooms possibly
[11:50:16] Leif H. Auke: a world view dont need that quick update.
[11:50:25] Thai Huynh: yep
[11:50:56] Leif H. Auke: for ex. zoom 1 every minute, and zoom 17 every 10 second and rest in between ?
[11:51:05 | Redigert 11:51:12] Thai Huynh: its depend on zoom level from user
[11:51:43] Leif H. Auke: data structure ...
[11:52:34] Leif H. Auke: we send tracker ID to UI, but on summarices positions we dont have tracker ID, but insead a figure = number of trackers on positions
[11:52:48] Leif H. Auke: I think its ony a minor adjustment ?
[11:52:56] Duong Thanh Huy: it is
[11:53:14] Duong Thanh Huy: so that means it is just for the number of trackers
[11:53:31] Leif H. Auke: yepp
[11:53:31] Duong Thanh Huy: showing drones moving is still the same?
[11:53:41] Leif H. Auke: yes
[11:53:57] Leif H. Auke: but for summarized level you possibly will not see any movements
[11:54:43] Leif H. Auke: I think is oly when you zoom in to individual drones (zoom > 17) (for ex) you will see anything move..
[11:55:05] Duong Thanh Huy: ok, so at which level we will see drones?
[11:55:52] Leif H. Auke: I think we summarize for level 1 to 17, above 17 se show individual drones ?
[11:56:31] Duong Thanh Huy: ok :)
[11:56:44] Duong Thanh Huy: but maybe 17 is a little bit too much
[11:57:11] Duong Thanh Huy: user will wonder why they don't see any drones when they are at level 14 for examples
[11:57:23] Duong Thanh Huy: just the number of drones
[11:57:50] Leif H. Auke: hmm
[11:58:18] Leif H. Auke: I calculated -> at zoom level 17 the with of the map will be 600 meters
[11:58:19] Leif H. Auke: ??
[11:58:26] Leif H. Auke: yes, maybe to small.
[11:59:03] Leif H. Auke: at zoom level 15 -> 2.5 KM
[11:59:57] Leif H. Auke: at zoom level 14 -> 4.9 KM
[12:00:19 | Redigert 12:00:34] Leif H. Auke: (rule is, map dooble in height and width for each zoom level up)
[12:00:20] Leif H. Auke: :)
[12:00:36] Duong Thanh Huy: thanks for the info
[12:00:37] Duong Thanh Huy: :)
[12:00:55] Leif H. Auke: (I did spend some hours yesterday study) :)
[12:01:05] Leif H. Auke: and figure out the function
[12:01:47] Thai Huynh: :)
[12:01:48] Leif H. Auke: oki, maybe 1 to 14 calculated
[12:01:56] Leif H. Auke: (we try, see how it looks)
[12:03:10 | Redigert 12:03:23] Thai Huynh: Okie, my summary >> still imrpove single web page, commit in todays. Remove more files un-used for js :) all refer to auke-js
[12:03:59] Leif H. Auke: cool
[12:04:10] Duong Thanh Huy: ok Leif, you will write an abstract for that?
[12:04:35] Duong Thanh Huy: honestly I'm a little bit confused how to proceed. Maybe I will screw up
[12:04:37] Leif H. Auke: yes, on this page https://wiki.cantara.no/display/drone/Layers+and+summarized+positions
[12:05:22 | Redigert 12:06:15] Leif H. Auke: you cant screw up any existing with this, Is added functionallity, with no change in existing :)
[12:05:32] Leif H. Auke: no problem............................... |-(
[12:06:02] Leif H. Auke: maybe I can make some stubs and commit
[12:06:12] Duong Thanh Huy: yes, that would be great
[12:06:20] Leif H. Auke: oki . i do
[12:06:36] Thai Huynh: better make more unit Test and then i and huy can study :)
[12:06:41] Duong Thanh Huy: thanks Leif
[12:06:57] Duong Thanh Huy: please pull first, we made some changes