zenith_azimuth_from_row_col: Map between zenith–azimuth angles and raster coordinates

In rcaiman: CAnopy IMage ANalysis

Map between zenith–azimuth angles and raster coordinates

Description

Bidirectional helpers to convert between angular coordinates on the hemispherical image (zenith, azimuth) and raster coordinates (row, col).

Usage

zenith_azimuth_from_row_col(z, a, row, col)

row_col_from_zenith_azimuth(z, a, zenith, azimuth)

Arguments

z	terra::SpatRaster generated with zenith_image().
a	terra::SpatRaster generated with azimuth_image().
row, col	numeric vectors. raster coodinates. Must have equal length.
zenith, azimuth	numeric vectors. Angles in degrees. Must have equal length.

Details

⁠zenith, azimuth⁠ → ⁠row, col⁠. A sparse set of valid sky points is sampled over the image and enriched with their angular coordinates. Two local least-squares surfaces (spatial::surf.ls, np = 6) are fitted to predict row and col as smooth functions of (azimuth, zenith). Predictions are rounded to the nearest integer index. Out-of-bounds indices are not produced under normal conditions; clamp externally if needed.

⁠row, col⁠ → ⁠zenith, azimuth⁠. Angles are obtained by direct lookup on z and a using terra::cellFromRowCol. If any queried cell is NA (e.g., outside the calibrated lens footprint), a synthetic z is reconstructed from the lens model attached to z (attribute lens_coef), and a is rebuilt with azimuth_image() using the stored orientation attribute in a. This yields robust angle retrieval near borders.

Value

See Functions

Functions

row_col_from_zenith_azimuth

Return image indices for given angles.

zenith_azimuth_from_row_col

Return angles in degrees for given image indices.

Examples

z <- zenith_image(1000, lens())
a <- azimuth_image(z)

rc <- row_col_from_zenith_azimuth(z, a, zenith = c(30, 60), azimuth = c(90, 270))
rc

ang <- zenith_azimuth_from_row_col(z, a, row = rc$row, col = rc$col)
ang

rcaiman documentation built on Sept. 9, 2025, 5:42 p.m.