Andrew Leach schrieb: > On Mar 15, 9:07 am, "neil.young" <[email protected]> wrote: > >> a) Querying for routes - OK >> b) Decoding returned polyline and levels - OK >> c) Transform polyline geocodes to picture coordinates and drawing the >> line - OK >> d) Question: How to interpret the level for each point? >> > > What the level does is to provide information about whether a > particular point is "necessary" at a particular zoom. Points are only > missed out if they will make no material difference to the shape of > the polyline. The relationship between letters and zoom levels is > explained by Professor McClure at > http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/description.html > > Hmm. Sorry for insisting. I'm not sure with the "particular zoom" claim.
Concerning http://code.google.com/intl/en/apis/maps/documentation/polylinealgorithm.html "An encoded level value of 3 in this case would ensure that a point appears in all zoom level, while a level of 0 will ignore points specified beyond zoom level 5. The endpoints of a polyline should often be set to the largest encoded level, to ensure that the endpoints will appear in all zoom levels and the line is drawn correctly." and further: Level 0 Zoom levels 0-5 Level 1 Zoom levels 6-10 Level 2 Zoom levels 11-14 Level 3 Zoom levels 15-18 Means to me: In the current realization (numLevels = 4) a level describes not a particular zoom (the encoding method used _could_, but it doesn't), but a group of zoom levels. And from all, what I can see, currently the 4 levels subdividing the available zoom stages into 4 groups (BTW, 18? Why 18?). With every increasing level a point is visible in more zoom stages (is "more visible"). I.e. from the spec a point at level 3 is visible at all zooms, but a point at level 0 just for zooms from 0 to 5. If a point is given level 1, it inherits 0-5 and adds zoom 6-10. If a point is at level 2, it inherits from level 0 and 1. The 3 has it all...This is my interpretation, but the Google spec is very unclear on this. To be more specific: Here is a direction (polyline and levels) returned by Google, describing a short drive in Berlin (from Brandenburg Gate to Großer Stern): 52.51639, 13.37819, Level 3 52.51625, 13.37821, Level 3 52.51625, 13.37821, Level 3 52.51629, 13.37951, Level 3 52.51629, 13.37951, Level 3 52.51638, 13.38084, Level 3 52.51638, 13.38084, Level 3 52.51674, 13.3807, Level 0 52.51809, 13.38044, Level 3 52.51809, 13.38044, Level 3 52.51787, 13.37725, Level 0 52.51779, 13.37696, Level 3 52.51779, 13.37696, Level 3 52.51705, 13.37723, Level 0 52.51681, 13.37727, Level 0 52.51668, 13.37722, Level 0 52.5165, 13.37698, Level 0 52.51629, 13.37686, Level 3 52.51629, 13.37686, Level 3 52.516, 13.37197, Level 0 52.51579, 13.36927, Level 0 52.51472, 13.35265, Level 0 52.51468, 13.35193, Level 0 52.51479, 13.35106, Level 3 52.51479, 13.35106, Level 3 52.51491, 13.35095, Level 0 52.5151, 13.3506, Level 0 52.51519, 13.35025, Level 0 52.5152, 13.34995, Level 1 52.51518, 13.34979, Level 0 52.51507, 13.34947, Level 0 52.51474, 13.34912, Level 3 The first "Level 0" after the initial 3s describes a small bend in the straight line between "The Adlon" and the left turn at Dorotheenstrasse, so I would understand, that this bend isn't necessary to be drawn at zooms below 5 (it isn't necessary for all zooms < 10, I would say). The last sequence 3 0 0 0 1 0 0 3 forms a curve with a radius of ~100m, I bet, this isn't really necessary to be shown, if Europe is in the scope. But I don't really understand the notation used in the documentation. If I'm right with my interpretation, the documentation should better say: Every next level adds this and that zoom level(s) to the zoom levels, a point is visible in. Am I right with this? If yes, 1 would _not_ mean "Visible from 6 to 10" (as implied by the doc) but visible from 0 to 10. Sure, you are not the right persons to address this, but interpretations welcome. > Andrew > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/Google-Maps-API?hl=en -~----------~----~----~----~------~----~------~--~---
