Fix empty point behaviour in wkb, ewkb, and hexewkb formats

Issue

When loading an empty point geometry encoded in one of the above formats, the coordinate doubles unpacked in WKB.class#getPoint are both NAN

  function getPoint(&$mem) {
    $point_coords = unpack("d*", fread($mem,$this->dimension*8));
    if (!empty($point_coords)) {
      return new Point($point_coords[1],$point_coords[2]);
    }
    else {
      return new Point(); // EMPTY point
    }
  }

Because of the NAN values, the empty point is able to bypass the safeguards in the Point.class constructor.

    // Basic validation on x and y
    if (!is_numeric($x) || !is_numeric($y)) {
      throw new Exception("Cannot construct Point. x and y should be numeric");
    }

This results in an invalid Point object, where $point->isEmpty() is false.

Observations

Postgres seems to implicitly encode POINT EMPTY as POINT(NAN, NAN), and by default returns the hexewkb representation.

Postgres:

Screen Shot 2021-12-02 at 11 08 25 PM

>>> select st_ashexewkb(st_geomfromtext('POINT EMPTY'));
=> "0101000000000000000000F87F000000000000F87F"

Verifying in PHP:

>>> bin2hex(pack('cLdd', 1, 1, NAN, NAN))
=> "0101000000000000000000f87f000000000000f87f"

Problems

1. Reading the above empty point binary with `GeoPhp`:

>>> geoPHP::load('0101000000000000000000F87F000000000000F87F')->asArray()
=> [
     NAN,
     NAN,
   ]

>>> geoPHP::load('0101000000000000000000F87F000000000000F87F')->isEmpty()
=> false

2. Empty Point binary output representation is invalid.

>>> bin2hex(geoPHP::load('0101000000000000000000F87F000000000000F87F')->out('ewkb'))
=> "0101000000"

>>> select st_astext('0101000000'::geometry)

=> [XX000] ERROR: WKB structure does not match expected size! Position: 18

Solutions

Check for is_nan in the Point.class constructor and create an empty point in that case.
Properly encode NAN values for an empty point binary representation.
Add test fixture for an empty point in ewkb format

*Note: this solution works for empty point geometries with different srid's as well.

phayes / geoPHP