Update geo-traits

[kylebarron]

Update for georust/geo@4764343 (#1157)

[michaelkirk]

I'm completely out of my depth with geoarrow, but this appears a little awkward. Does the push_point method even make sense anymore?

edit: as in, does it even need to exist?

[kylebarron]

It's a little awkward, and potentially could be refactored in the future/moved to the point builder, but at some level there needs to be a conversion between empty points and the GeoArrow representation of those, which is with NAN values.

[michaelkirk]

Yeah, I guess this comes down to my unfamiliarity with geoarrow.

So it sounds like a PointArray needs to have an element in its CoordBuffer for each point, even if that point is POINT EMPTY.

Is the validity: NullBuffer used to encode which coords correspond to POINT EMPTY?

[kylebarron]

So it sounds like a PointArray needs to have an element in its CoordBuffer for each point, even if that point is POINT EMPTY.

Correct.

The raw layout for a 2D point array with 4 points is:

[0, 2, 4, 5, NaN, NaN, 10, 2]

This translates to

Point(0, 2),
Point(4, 5),
Point EMPTY,
Point(10, 2)

Is the validity: NullBuffer used to encode which coords correspond to POINT EMPTY?

No... With GeoArrow we have three states of geometry:

• null: this is a row that does not have a geometry
• empty: this row has a geometry but its geometry is empty (e.g. as a result of an empty intersection)
• valid and non-empty: a standard geometry

The validity: NullBuffer encodes the first of those. Every Arrow array has an optional nullability buffer, and that can say "this row is null".

When that validity buffer says that a row is valid, then we can look into the encoded geometry buffer, but it's still possible for that encoded geometry to be empty.

So for a 2D point, the encoding is one of these three states:

• null: validity buffer indicates value is null. For a point array the memory still needs to be reserved so that the offsets of future points are correct, but the values of that point's coordinates are undefined.
• empty: validity buffer indicates not null. But all values are f64::NAN.
• valid: validity buffere not null, values are not f64::NAN.