Tanaka contours

Joaquim · November 5, 2025, 12:14am

I find these contour plots very cute, and now finally implemented it in GMT.jl

using GMT

G = grdcut("@mars_relief_02m", R="220/233/13/25");
contourf(G, tanaka=true, title="Tanaka Olympus", show=1)

PlanetGus · November 5, 2025, 1:42pm

It’s (grd)contour with illumination on the iso (pen)?
Is it doable with pure gmt?

Joaquim · November 5, 2025, 2:02pm

See the (short) code. Quite Matlabish to read. Doable in bash, you mean? Yep, eventually.

github.com/GenericMappingTools/GMT.jl

src/contourf.jl

master


      
          function tanakacontour(G, d, azim)
          	# Tanaka contours are contour lines whose thickness and intensity vary based
          	# on illumination direction, creating an illusion of 3D relief. Illuminated
          	# slopes get lighter/thinner lines, shaded slopes get darker/thicker lines.
          
          	illum = grdgradient(G, azimuth=azim, norm="e0.5+a0.5")	# Means result is in 0-1 range
          	cont = append!(d[:C].range[:,1], d[:C].range[end])		# Contour levels from CPT
          	C = grdcontour(G, cont=cont, dump=true)
          	n_contours = length(C)
          	delete!(d, [:C]);	delete!(d, [:title]);	# If passed, it was used already
          	gray = makecpt(cmap=:gray, range=(-0.6,1.05))
          	min_lw, diff_lw = 0.8, 0.7				# max_lw = min_lw + diff_lw, the thikest line width at the darkest sides
          
          	sampled = grdtrack(C, grid=illum)		# Sample illumination values along this contour
          	for contour = 1:n_contours				# Process each contour segment
          		# Draw contour segments with varying properties
          		n_pts = size(C[contour].data, 1)
          		lw = Vector{Float64}(undef, n_pts-1)
          		for i in 1:n_pts-1
          			# Average illumination for this contour

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