[mkgmap-dev] Configurable flood blockerFrom Felix Hartmann extremecarver at gmail.com on Sun Dec 19 18:34:06 GMT 2010
On 19.12.2010 18:17, WanMil wrote: >> >>> Felix, >>> >>> there is nothing to check. The flood blocker works only in >>> multipolygon mode. It is not possible to implement that for the >>> polygon mode. >>> >>> Where do you think is the advantage of the polygon mode? >>> >>> WanMil >> The advantage is: >> >> a) Speed (if you use --transparent and then gmt to set the transparency >> to no) you can have for land one polygon (only land area) for sea one >> polygon (only sea area) and NO background polygon. >> b) overlapping maps - using --transparent there is less chance that a >> land polygon from one map, overlaps sea from another map (on GPS as only >> there can be several maps active at the same time). >> >> >> --- in principal there is no speed advantage - but only as long as one >> does not attribute a color to 0x4b, however as one colors the >> background/land to be say white, it is much quicker to have white land >> background only, otherwise the GPS has to read much more data, and on >> older generation GPS when panning the map, there is a notable speed >> difference on top of flahing up background color, until it is overdrawn >> by the real landuse/natural/... polygon. > > I don't want to put into question your final observation (polygon > renders quicker on GPS device) but I cannot follow your arguments. > Let's try to sort it out. Please correct me at any point if I am wrong. > > I have added a picture for both sea generation methods. It shows the > resulting tile and all polygons contained in the tile. > > * First of all the new mp code in the coast branch generates land > polygons. This is a new feature. So land+sea polygons=tile. > * The polygon code creates one sea polygon covering the whole tile and > adds all land polygons. The style implementor must ensure that land is > drawn over sea. Otherwise the tile is flooded. > * For tiles that don't contain any see one land polygon covering the > whole tile is created (both for polygon and multipolygon processing). > > => a): For both variants you don't need a background polygon. The > whole tile is covered by sea or land. > => b): I don't understand where there should be the difference between > polygon and multipolygon processing. > => in principal: Do you mean that you don't want to paint land > polygons but instead the background polygon? Ok, but in this case you > can ignore the land polygon in the multipolgon variant but not in the > polygon variant. Otherwise the background is painted and after that > the sea is painted over it and you get flooded tiles. So you need to > color the land polygons. > > The multipolygon processing generates much more complex polygons. I > think that's the reason why it is rendered more slowly on GPS devices. > > WanMil I have not checked the speed after the change on GPS. I'll do that and then report back. Before definitely the quickest was --transparent and --polygons. (as I set the opqaque switch with gmaptool afterwards, I of course colored the land polygon - but the maps had no background polygon at all).
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