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Support on-the-fly geometry clipping #1116
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initial support for geometry clipping : https://github.com/mapnik/mapnik/tree/move_bind_logic_to_layer |
@artemp - do you see a possible way to make clipping on/off per user control? This seems important in the case that we find clipping may not be desirable and also quite useful for testing. |
@springmeyer - we can, but I'm hoping that 'clipping' will be always desirable. Also, we can make clip_box configurable. |
@springmeyer I think we should leave ras.clip_box |
@artemp - yes, leaving ras.clip_box sounds good. I did a test with I have Anyway, I'm also now not seeing a major perf hit at z0 with clipping vs no-clip branch. So, I'm not sure what I was seeing before :) |
landed in 514ec14 |
we're considering pre-clipping vectors prior to get into mapnik (using queries or temporary tables in postgis). Can we opt-out of this to not incurr in the overhead ? (see issue #1093) |
@strk - yes, I'm currently working on allowing disabling of clipping for text labels. I'll take a look at what it would take for polygons/lines. However, first we'd need to ensure the perf issue you are seeing is due to clipping. |
I'm seeing line pattern problems in 2.1 that weren't there in 2.0. Issue #777 addresses what I'm seeing but you seem to be of the opinion that it is fixed so I'm raising it here: This is from a tile server with Mapnik 2.1.0+dev20120615.git.b12e73f. The magenta road in the middle straddles a meta tile boundary. This is the same server with 2.0.1+dev20120518.git.92dd305-1: Sorry for reporting against a 10-day old version, it's entirely possible that it was just a glitch that has been fixed in the mean time. |
@woodpeck - thanks for reporting |
We can support geometry clipping.
It can potentially be:
VertexSource
in ctrans.hppThis can enable:
Faster rendering times for maps with a density of complex, large, and/or multi-part features, particularly at >= z10.
Cool cartography effects - e.g. allowing label centroids to be sensitive to the clipped polygon region (Labeling polygons that are "majority outside of tile bbox" #25)
Infinite zooming - currently >= z18-20 maps that intersect with very large polygons can cause overflows in AGG (rendering overflow #1076, features unrendered at >= z11 when agg clipping not used #1075)
Complementing AGG's
clip_box()
functionality, which works in screen coords.This ticket replaces #708, #876, #25, #1076, and #1075
details
It should be controllable by user (#1281), likely at the symbolizer level. For example, clipped geometries will likely not work well for labels along lines.
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