Monitor - vector tiles

[vmarc]

Today, when displaying monitor maps, the details about the routes, deviations and segments are sent to the browser in geojson format. The geojson contains the coordinates of all nodes in all ways, independent of the zoom level. This is also how it works in waymarked trails when highlighting a particular route on the map. This worked very well for the routes that were originally added in the monitor. It was known from the start that with large routes being added to the monitor this would not scale very well. The amount of data that has to be sent to the browser for cross-continent routes is just too large and takes too much time. This is why for super-routes the map always just shows the information per sub-relation, and there is no map for relations only containing other relations.

Issues have been opened asking for also displaying complete super-routes (see issues #361, #356 and also to lesser extent #352). With the current technique of shipping geojson this would lead to unacceptable performance.

A solution that would scale better for large routes would be to use vector tiles instead of geojson (just like is done today for node network routes). This would allow to only ship the amount of data that is appropriate for the current zoom level (DouglasPeuckerSimplifier).

[vmarc]

Some initial investigation, these are more or less the number of tiles that have to be generated per zoom level:

level	tile count
2	4
3	6
4	12
5	27
6	79
7	230
8	645
9	1676
10	4248
11	10253
12	23999
13	54249
14	119737
total	215165

[vmarc]

Some further investigation: what would it take to do hiking- and bicycle-route analysis and vector tile generation for all routes worldwide?

route	type	node_network	other	total
bicycle	route	40 983	66 155	107 138
bicycle	superroute	0	1 062	1 062
foot	route	42 958	12 233	55 191
foot	superroute	0	43	43
walking	route	0	131	131
walking	superroute	0	4	4
hiking	route	45 371	168 382	213 753
hiking	superroute	0	1 304	1 304
mtb	route	30	16 898	16 928
mtb	superroute	0	67	67
inline_skates	route	55	166	221
inline_skates	superroute	0	3	3
motorboat	route	454	1	455
motorboat	superroute	0	0	0
canoe	route	350	287	637
canoe	superroute	0	3	3

• node network routes: 130 201

• non node network routes: 266 739

• total routes: 396 940

Estimated size for mongodb monitor-relations collection: 700Mb.

Time to create monitor-relations collection with 4038 relations (reading relations from overpass database one by one) remote: 1:30h, non-remote: 1:05h.

Estimated time to create all remote: 6 days!

[vmarc]

Additional test to create collection monitor-relations remotely, but using batches of 100 routes for the requests to the Overpass API database, estimate: 25 hours.