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indexers.go
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/
indexers.go
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package pixidb
import (
"github.com/owlpinetech/flatsphere"
"github.com/owlpinetech/healpix"
)
// Common functionality for converting between various different coordinate systems and
// pixel indices within a store.
type LocationIndexer interface {
ToIndex(Location) (int, error)
Projection() flatsphere.Projection
Name() string
Size() int
}
// Simple indexing into a grid, no spherical projection provided by this indexer. Supports
// either row-major or column-major storage of the data for particular access patterns.
type ProjectionlessIndexer struct {
Width int `json:"width"`
Height int `json:"height"`
RowMajor bool `json:"rowmajor"`
}
func NewProjectionlessIndexer(width int, height int, rowMajor bool) ProjectionlessIndexer {
return ProjectionlessIndexer{
Width: width,
Height: height,
RowMajor: rowMajor,
}
}
func (p ProjectionlessIndexer) Name() string {
return "projectionless"
}
func (p ProjectionlessIndexer) Projection() flatsphere.Projection {
return nil
}
func (p ProjectionlessIndexer) Size() int {
return p.Width * p.Height
}
func (p ProjectionlessIndexer) ToIndex(loc Location) (int, error) {
switch val := loc.(type) {
case IndexLocation:
return int(val), nil
case GridLocation:
if p.RowMajor {
return val.Y*p.Width + val.X, nil
}
return val.X*p.Height + val.Y, nil
default:
return -1, NewLocationNotSupportedError(p.Name(), loc)
}
}
// Indexing into a sphere of pixels project via a standard Mercator projection. Because
// Mercator diverges at the poles, two cutoff parameters are provided for the northern
// and southern latitudes. These cutoff parallels will mark the boundaries of the top
// and bottom of the grid respectively. Supports either row-major or column-major storage
// of the data for particular access patterns.
type MercatorCutoffIndexer struct {
NorthCutoff float64 `json:"northCutoff"`
SouthCutoff float64 `json:"southCutoff"`
southProj float64 // precomputed projected south latitude
latRangeProj float64 // precomputed (North - South) latitude projected range
Grid ProjectionlessIndexer
proj flatsphere.Mercator
}
func NewMercatorCutoffIndexer(northCutoff float64, southCutoff float64, width int, height int, rowMajor bool) MercatorCutoffIndexer {
if northCutoff <= southCutoff {
panic("pixidb: mercator north cutoff smaller than south cutoff")
}
proj := flatsphere.NewMercator()
_, southY := proj.Project(southCutoff, 0)
_, northY := proj.Project(northCutoff, 0)
return MercatorCutoffIndexer{
NorthCutoff: northCutoff,
SouthCutoff: southCutoff,
southProj: southY,
latRangeProj: northY - southY,
Grid: NewProjectionlessIndexer(width, height, rowMajor),
proj: flatsphere.NewMercator(),
}
}
func (m MercatorCutoffIndexer) Name() string {
return "mercator-cutoff"
}
func (m MercatorCutoffIndexer) Projection() flatsphere.Projection {
return m.proj
}
func (m MercatorCutoffIndexer) Size() int {
return m.Grid.Size()
}
func (m MercatorCutoffIndexer) ToIndex(loc Location) (int, error) {
switch val := loc.(type) {
case IndexLocation:
return int(val), nil
case GridLocation:
return m.Grid.ToIndex(loc)
case SphericalLocation:
if val.Latitude > m.NorthCutoff || val.Latitude < m.SouthCutoff {
return -1, NewLocationOutOfBoundsError(loc)
}
x, y := m.proj.Project(val.Latitude, val.Longitude)
return m.ToIndex(ProjectedLocation{x, y})
case ProjectedLocation:
bounds := m.proj.PlanarBounds()
xPix := ((val.X - bounds.XMin) / bounds.Width()) * float64(m.Grid.Width-1)
yPix := ((val.Y - m.southProj) / m.latRangeProj) * float64(m.Grid.Height-1)
return m.ToIndex(GridLocation{int(xPix), int(yPix)})
case RectangularLocation:
return m.ToIndex(val.ToSpherical())
default:
return -1, NewLocationNotSupportedError(m.Name(), loc)
}
}
// Indexing into a sphere of pixels projected via a cylindrical equirectangular projection.
// 0,0 is the bottom left corner of the projection space, i.e. (XMin, YMin) => (0, 0). Supports
// both row-major and column-major order of the grid, which changes how efficient certain
// consecutive x- or y-accesses are, but does not change where x,y coordinates refer to.
type CylindricalEquirectangularIndexer struct {
Parallel float64 `json:"parallel"`
Grid ProjectionlessIndexer
proj flatsphere.Equirectangular
}
// Create a new indexer into a grid with the cylindrical equirectangular projection, focused at
// the given latitude. Many common projections can be created this way.
func NewCylindricalEquirectangularIndexer(parallel float64, width int, height int, rowMajor bool) CylindricalEquirectangularIndexer {
return CylindricalEquirectangularIndexer{
Parallel: parallel,
Grid: NewProjectionlessIndexer(width, height, rowMajor),
proj: flatsphere.NewEquirectangular(parallel),
}
}
func (c CylindricalEquirectangularIndexer) Name() string {
return "cylindrical-equirectangular"
}
func (c CylindricalEquirectangularIndexer) Projection() flatsphere.Projection {
return c.proj
}
func (c CylindricalEquirectangularIndexer) Size() int {
return c.Grid.Size()
}
func (c CylindricalEquirectangularIndexer) ToIndex(loc Location) (int, error) {
switch val := loc.(type) {
case IndexLocation:
return int(val), nil
case GridLocation:
return c.Grid.ToIndex(loc)
case SphericalLocation:
x, y := c.proj.Project(val.Latitude, val.Longitude)
return c.ToIndex(ProjectedLocation{x, y})
case ProjectedLocation:
bounds := c.proj.PlanarBounds()
xPix := ((val.X - bounds.XMin) / bounds.Width()) * float64(c.Grid.Width-1)
yPix := ((val.Y - bounds.YMin) / bounds.Height()) * float64(c.Grid.Height-1)
return c.ToIndex(GridLocation{int(xPix), int(yPix)})
case RectangularLocation:
return c.ToIndex(val.ToSpherical())
default:
return -1, NewLocationNotSupportedError(c.Name(), loc)
}
}
// Pixelizes a sphere using the HEALPix pixelisation method. This indexer promises a
// single resolution pixelization, where every pixel has the same angular area. Provides
// storage options of both ring and nested schemes, for making certain data-access patterns
// more efficient.
type FlatHealpixIndexer struct {
Scheme healpix.HealpixScheme `json:"scheme"`
Order healpix.HealpixOrder `json:"order"`
proj flatsphere.HEALPixStandard
}
func NewFlatHealpixIndexer(order healpix.HealpixOrder, scheme healpix.HealpixScheme) FlatHealpixIndexer {
return FlatHealpixIndexer{
Scheme: scheme,
Order: order,
proj: flatsphere.NewHEALPixStandard(),
}
}
func (h FlatHealpixIndexer) Name() string {
return "flat-healpix"
}
func (h FlatHealpixIndexer) Projection() flatsphere.Projection {
return h.proj
}
func (h FlatHealpixIndexer) Size() int {
return h.Order.Pixels()
}
func (h FlatHealpixIndexer) ToIndex(loc Location) (int, error) {
switch val := loc.(type) {
case IndexLocation:
return int(val), nil
case RingLocation:
return healpix.RingPixel(int(val)).PixelId(h.Order, h.Scheme), nil
case NestLocation:
return healpix.NestPixel(int(val)).PixelId(h.Order, h.Scheme), nil
case UniqueLocation:
return healpix.UniquePixel(int(val)).PixelId(h.Order, h.Scheme), nil
case SphericalLocation:
return healpix.NewLatLonCoordinate(val.Latitude, val.Longitude).PixelId(h.Order, h.Scheme), nil
case ProjectedLocation:
return healpix.NewProjectionCoordinate(val.X, val.Y).PixelId(h.Order, h.Scheme), nil
case RectangularLocation:
return h.ToIndex(val.ToSpherical())
default:
return -1, NewLocationNotSupportedError(h.Name(), loc)
}
}
// TODO: example of how to get sinusoidal into a grid
// https://modis-land.gsfc.nasa.gov/MODLAND_grid.html