Hey Mark I think you are over thinking it ;)
Iface.mapCanvas().extent() will give you the event of the view. Extent.center() for the middle. You can transform this using the coordinate transformation classes. Nathan On Jun 14, 2014 8:59 AM, "Mark Coletti" <mcole...@gmail.com> wrote: > First, long time no see! Been a while since I've posted to this mailing > list. ;) > > I'm developing a plug-in that will allow a user to use the Twitter REST > API to create a layer of tweets. Yes, I already know of the articles on > the net regarding how to do that manually. However, I'm wrapping that > functionality in a nice GUI to shield the lay user from messing about with > code. > > I already have the plugin working with specified lat/lon coordinates and a > given radius. That's the easy part. What I'd also like to do is have the > user specify such things as "gimme the tweets for the current layer extent" > or "gimme the tweets for just the area in the viewport." I *suspect* that > these are easy, but my first pass through the available high level > documentation didn't give me a whole lot to steer by. > > For the first scenario, I would need to do the following: > > > 1. get the current layer > 2. get the MBR for said layer > 3. compute the centroid/midpoint > 4. project to lat/lon if necessary > 5. compute distance from midpoint to edge > > Step #1 would, I presume, entail talking to the singleton layer manager to > get the currently selected layer. Step #2 would presumably be available in > the corresponding QgsLayer object. Step #3 I could use the GEOS geometry > ops to compute. Step #4 would be a bit tricky since I'd have to first > determine if reprojection was even necessary, and if so then jump through > the hoops to get my lat/lon. Step #5 I note the existence of QgsDistance, > which I could use to compute the distance from the centroid to an edge of > the layer MBR; doing a flat or ellipsoidal distance calculation would > depend on the CRS of the selected layer, natch. > > My nagging feeling is "surely this, or a subset of these, is/are common > use cases" ... and that there'd be corresponding syntactic sugar for > implementing them. The QgsDistance class is sort of an example since it > presumably handles projection and geometric distance headaches for you in > desired units. > > So, does there exist such a set of convenience classes/functions? > Similarly does there exist somewhere a set of corresponding code snippets? > (The official online code snippets don't cover these, alas.) > > Cheers! > > Mark > -- > mcole...@gmail.com > > > _______________________________________________ > Qgis-developer mailing list > Qgis-developer@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-developer >
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