Changelog • tissot

tissot 0.3.0

tissot() gains a method argument (default "proj"). The new "proj" method delegates to PROJ::proj_factors(), calling the PROJ C library directly for exact distortion factors rather than approximating them via finite differences. This is more accurate, especially for tabular or piecewise projections (e.g. Robinson). The original finite-difference computation (Snyder 1987), inspired by Bill Huber’s formulation at https://gis.stackexchange.com/a/5075/482, is preserved as method = "finitediff". The PROJ package is now the sole coordinate transformation dependency; gdalraster has been removed.
tissot_raster() computes distortion surfaces on a regular projected grid, returning a tissot_raster object with image() and plot() methods. Extent is auto-detected from the global lon/lat bounding box (clamped by radius) or supplied explicitly. Supports any metric from [tissot()] output.

gdalraster removed from Imports. All coordinate transformation now goes through PROJ::proj_trans() and PROJ::proj_crs_text(). CRS validation (srs_is_geographic) is handled by an internal helper using PROJ::proj_crs_text().

Fixed default metrics in tissot_raster(): names now use underscores ("scale_area", "scale_h", "scale_k") matching the actual tissot_tbl column names (previously used dots, causing silently all-NA output).

CRAN release: 2026-02-12

Major refactor — modernized engine, new API, and rich plotting.

Projection engine switched from reproj to transform_xy() from gdalraster. All projection work is now a single batched GDAL call.
API renamed: proj.in/proj.out → source/target, following reproj conventions. target is the second positional argument (required); source defaults to "EPSG:4326".
tissot() input is now any “xy-ish” object (matrix, data.frame, list, length-2 vector) via the internal as_xy() helper. The old lambda/phi positional arguments are replaced by x.
tissot() returns a tissot_tbl (subclassed tibble) with source and target stored as attributes. Column names changed to: x, y, dx_dlam, dy_dlam, dx_dphi, dy_dphi, scale_h, scale_k, scale_omega, scale_a, scale_b, scale_area, angle_deformation, convergence.
indicatrix() returns an indicatrix_list (replaces indicatrixes class). Accepts tissot_tbl or raw coordinates + explicit target.
Removed: indicatrix0(), tissot0(), .prj(), and the internal numericDeriv path. The Jacobian is now computed directly via finite differences.

plot.indicatrix() and plot.indicatrix_list() with:
- Reference unit circle overlay (show.circle)
- Lambda/phi direction axes (show.axes)
- show.circle and show.axes accept TRUE, FALSE, or a named list of graphical parameters for full customization
- Colour-coded fill via fill.by (e.g. "scale_area", "angle_deformation")
print() and summary() methods for tissot_tbl.
print(), length(), and [ methods for indicatrix_list.
tissot_map() and tissot_abline() accept explicit target argument.
as_xy() internal helper coerces diverse coordinate inputs.
resolve_gpar() internal helper for the logical-or-list graphical parameter pattern.