radius=0 leads to zero results with PIP

[mapsam]

When radius is 0, we expect point in polygon style results (ie 1 result if we’re within a single polygon). Right now we get zero results since the query point is a double (lng lat) but by the time we’re comparing the distance from closest_point we’re in integers, which then get converted to a lng lat and can be different than the original query point since it’s an interpolation. This means the distance check looks something like if (0.00011241241 <= 0) { ... } which evaluates to false.

Three possible solutions:

1. We’ll want to use something other than closest_point for PIP (radius=0) operations
2. Do all calculations in doubles instead of ints
3. Instead of using zero (if radius is zero) we use some sort of very small number like if (0.0000234 < 0.5) to catch these instances

cc @flippmoke

[mapsam]

Per chat with @flippmoke we've got a relatively solid solution for this problem. Basically, closest_point won't work for point in polygon use-cases if we work in integer space. In the name of cleanliness and performance, point-in-polygon should probably be a different code path or method entirely. Before we split them apart, here's the route I'll go down:

• radius > 0: stick with current case as-is () then we treat it as closest_point algorithm in ints (or doubles) and try to find the distance in ints (or doubles) with what we have.
• radius = 0: run down a different code path with either intersects/within (via spatial-algorithms), and start thinking about these two use-cases as separate methods in vtquery.

Once we get this working, splitting the code paths out into two methods could be helpful, giving the implementers (JS devs) opportunity to use two different methods depending on their needs. For example:

// current radius-based query
vtquery.closest(tiles, ll, options, cb);

// point in polygon method 
// (since the implement will know if they are working with radius=0)
// probably work within doubles space and only worry about polygons
vtquery.within(tile, ll, options, cb); 

// OR - if we are dealing with integer space and want to 
// return points/polylines as possible features
vtquery.intersects(tile, ll, options, cb);

[mapsam]

Radius 0 is now part of #42 . We are using the internal mechanism of closest_point to verify the value is 0.0 (and not less than 0.0).