On Aug 2, 2011, at 1:47 PM, Alastair Aitchison wrote: > Hi list, > > I'm trying to plot OS Mastermap data using Mapnik, and am having a bit of > trouble with the placement of the cartographic labels. > Rather than having the labels sourced from shape attributes, the dataset > defines all label text as separate features with: > - a point location > - the anchor location of the text relative to the point (i.e. Top left, > Middle bottom etc.) > - the angle at which the text should be oriented (rather curiously, measured > as an integer value in 10ths of a degree from 0 - 3599) > > If I use a TextSymbolizer with placement=point, then I can place the labels > at the correct position relative to the point using a combination of the > vertical_alignment and dx/dy properties, but there doesn't seem to be any way > to specify the angle at which the text should be drawn. (i.e. there's no > equivalent to MapServer's ANGLE property)
Mapnik2/trunk does support angles, and reading them from a database field. So, this will be available in the next release. Also Hermann Krauses recent work, also just in the trunk development code, has support for anchors: http://mapnik.org/news/2011/jul/13/new_text_placement_system/ > > So, instead, I've been applying some old-school trigonmetry to artificially > create lines at the appropriate angle, either starting or ending at the > anchor point in question, and drawing the text on the line using a > TextSymbolizer with the placement=line model instead. It's a lot slower, > since it's probably invoking lots of clever "wrapping text to wiggly lines" > computations that aren't required for my single line segment scenario, but it > does (nearly) get the results I want. > The problem I now have is that, by using the placement=line model, I appear > to have sacrificed the ability to specify whereabouts along the line the > label gets placed - there is no horizontal-alignment attribute when using a > TextSymbolizer on a line as far as I can tell - the label is always placed in > the centre of the line. Yes, unfortunately horizontal-alignment is not yet implemented for line placement. > That means the only way I can get the label drawn in the right place is if I > create the line to be exactly of the right length for the label to fit. If I > create it too big, the label is effectively "padded" away from its anchor > point (which lies at one end of the line) and misplaced. But, if I create the > line too small, the TextSymbolizer label attached to it won't be rendered at > all. The problem is that, seeing as I'm using a non-fixed width font, the > length of the text string (and therefore the offset) is different for every > individual label - I've tried computing an approximate line length per length > of label, but it's not reliable enough to be used. > > Does anybody have any smart workarounds (or perhaps, a magical text-angle > property that I'm unaware of!) as to how to create angled text anchored to a > point? See above! :) > > Thanks! > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
