Handling negative buffer with NaN coordinates

Based on https://github.com/Turfjs/turf/pull/736#issuecomment-301937747, I wanted to add this morphological closing behavior to the test cases, however I noticed when entering a radius which is greater than the polygon, the geometry’s coordinates will result in NaN values.

Question: Is this expected output correct? Or should we return undefined or an empty FeatureCollection?

Example

https://jsfiddle.net/pvLx12n1/

const poly = turf.polygon([[[11, 0], [22, 4], [31, 0], [31, 11], [21, 15], [11, 11], [11, 0]]]);
turf.buffer(poly, -500, 'miles').geometry.coordinates;
//=[ [ NaN, NaN ] ]

Output Geometry

Seems like this output would be an invalid GeoJSON Polygon

{
  "type": "Feature",
  "properties": {},
  "geometry": {
    "type": "Polygon",
    "coordinates": [[null, null]]
  }
}

CC: @rafaelalmeida

[rafaelalmeida]

Agreed. If there’s an easy mechanism to return error details along with response, maybe it could be used if the cost to implement is low enough. Otherwise, a quick note in the docs would suffice, like:

“When using a negative radius, the resulting geometry may be invalid if it’s too small compared to the radius magnitude. If the input is a FeatureCollection, only valid members will be returned in the output FeatureCollection - i.e., the output collection may have fewer members than the input, or even be empty.”

While this does not say exactly what failed, should give devs a hint on where to look.

On Thu, May 18, 2017 at 2:37 PM, Denis [e-mail] wrote:

Yes, if a feature collection of 2 polygons is the input and only 1 of them has valid geometry, then the FeatureCollection will only contain 1 polygon.

Returning a “bad” geometry would most likely cause things to break by having NaN in the coordinates.

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/Turfjs/turf/issues/745#issuecomment-302485783, or mute the thread https://github.com/notifications/unsubscribe-auth/AA23X61mfpX89C6pgOIVXkcGslw8pi2-ks5r7IHOgaJpZM4NdP9o .

[DenisCarriere]

Yes, if a feature collection of 2 polygons is the input and only 1 of them has valid geometry, then the FeatureCollection will only contain 1 polygon.

Returning a “bad” geometry would most likely cause things to break by having NaN in the coordinates.