viewbox-query-planner

calculate rectangular bbox regions to query as a viewbox pans across 2d data

If you have a spatial database, you can query rectangular regions by the bboxes emitted from the update() function as a user pans a map. You'll also want to cull the results from old bboxes as keeping old bboxes around that don't intersect the current viewbox slows down the polygon operations.

In the future this module might use polygon clipping routines specific to rectilinear polygon geometry, which might speed things up considerably.

example

var vplan = require('viewbox-query-planner')()
vplan.add([0.5,0.5,1.5,1.5])
vplan.add([0.2,-0.1,1.1,0.6])

var boxes = vplan.update([0,0,1,1])
console.log(boxes) // [ [ 0, 0, 0.2, 1 ], [ 0.2, 0.6, 0.5, 1 ] ]

There is a more involed graphical demo in example/demo.js which you can view here: https://substack.net/demo/viewbox-planner.html

api

var viewboxQueryPlanner = require('viewbox-query-planner')

var vplan = viewboxQueryPlanner()

Create a new viewbox query planner instance vplan.

The planner will maintain a rectilinear polygon that you can grow or shrink with bboxes.

Ususally you will want to vplan.add() the boxes you get back from vplan.update() and cull old boxes that no longer intersect the viewbox.

vplan.add(bbox)

Add a bbox of the form [xmin,ymin,xmax,ymax] to the rectilinear polygon.

vplan.subtract(bbox)

Subtract a bbox of the form [xmin,ymin,xmax,ymax] from the rectilinear polygon.

var boxes = vplan.update(viewbox)

Return an array of bboxes of the form [xmin,ymin,xmax,ymax] that completely cover without overlapping the parts of the viewbox (of the form [xmin,ymin,xmax,ymax]) that are not covered by the internal rectilinear polygon.

install

npm install viewbox-query-planner

license

bsd