Off-axis projection with Mera

Project hydro / RT / gravity / particle data along any line of sight, not just the box axes. An off-axis projection is orthographic: the observer is at infinity, so all sightlines are parallel; each cell is carried along the line of sight onto the image plane.

This notebook follows the Off-axis Projection documentation. Pixel size is set physically with pxsize=[size, :unit] (preferred over res). Run the cells top to bottom and change the numbers to play around.

# --- environment ---------------------------------------------------------
# These tutorials use the development version of Mera in this repository.
# Point Pkg at your Mera.jl checkout (adjust the path), or delete these two
# lines if Mera is already in your default environment.
using Pkg
Pkg.activate(expanduser("~/Documents/codes/github/Mera.jl"))

using Mera, CairoMakie
CairoMakie.activate!()
println("threads = ", Threads.nthreads())

  Activating 

project at `~/Documents/codes/github/Mera.jl`


[ Info: Precompiling Mera [02f895e8-fdb1-4346-8fe6-c721699f5126] (cache misses: wrong dep version loaded (12), mismatched flags (6))

SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up

SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up

SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up

SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up



*__   __ _______ ______   _______ 
|  |_|  |       |    _ | |   _   |
|       |    ___|   | || |  |_|  |
|       |   |___|   |_||_|       |
|       |    ___|    __  |       |
| ||_|| |   |___|   |  | |   _   |
|_|   |_|_______|___|  |_|__| |__|




SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up

SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up
[ Info: Precompiling CairoMakie [13f3f980-e62b-5c42-98c6-ff1f3baf88f0] (cache misses: wrong dep version loaded (18))



SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up


[ Info: Precompiling PolynomialsMakieExt [6a4b1961-d857-5aa3-b7f6-fc7c46de29bb] (cache misses: wrong dep version loaded (18))



SYSTEM: caught exception of type :MethodError while trying to print a failed Task notice; giving up


threads = 4

Load a galaxy

Set the path/output of a simulation you have. The examples below use the Mera test galaxies; change BASE to your own data directory.

BASE = "/Volumes/FASTStorage/Simulations/Mera-Tests"   # <-- change me
info = getinfo(100, joinpath(BASE, "spiral_clumps"), verbose=false)
gas  = gethydro(info, verbose=false, show_progress=false)

  0.749615 seconds (3.91 M allocations: 303.434 MiB, 1.29% gc time, 102.12% compilation time)





HydroDataType(Table with 590311 rows, 10 columns:
Columns:
#   colname  type
────────────────────
1   level    Int64
2   cx       Int64
3   cy       Int64
4   cz       Int64
5   rho      Float64
6   vx       Float64
7   vy       Float64
8   vz       Float64
9   p        Float64
10  metallicity Float64, InfoType(100, "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps", FileNamesType("/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/info_00100.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/amr_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/hydro_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/hydro_file_descriptor.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/grav_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/part_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/part_file_descriptor.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/rt_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/rt_file_descriptor.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/info_rt_00100.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/clump_00100.", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/timer_00100.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/header_00100.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/namelist.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/compilation.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/makefile.txt", "/Volumes/FASTStorage/Simulations/Mera-Tests/spiral_clumps/output_00100/patches.txt"), "RAMSES", Dates.DateTime("2023-05-12T22:47:36.638"), Dates.DateTime("2025-06-21T18:31:55.533"), 4, 3, 3, 7, 100.0, 9.9335244067439, 1.0, 1.0, 1.0, 0.0, 0.0, 0.045, 3.085677581282e21, 6.77025430198932e-23, 1.9890999999999996e42, 6.559266058737735e6, 4.70430312423675e14, 1.6667, true, 6, 8, 0, [:rho, :vx, :vy, :vz, :p, :metallicity], [:epot, :ax, :ay, :az], [:vx, :vy, :vz, :mass, :family, :tag, :birth, :metals], Symbol[], [:index, :lev, :parent, :ncell, :peak_x, :peak_y, :peak_z, Symbol("rho-"), Symbol("rho+"), :rho_av, :mass_cl, :relevance], Symbol[], DescriptorType(1, [:density, :velocity_x, :velocity_y, :velocity_z, :pressure, :metallicity], ["d", "d", "d", "d", "d", "d"], false, true, 1, [:position_x, :position_y, :position_z, :velocity_x, :velocity_y, :velocity_z, :mass, :identity, :levelp, :family, :tag, :birth_time, :metallicity], ["d", "d", "d", "d", "d", "d", "d", "i", "i", "b", "b", "d", "d"], false, true, [:epot, :ax, :ay, :az], false, false, 0, Dict{Any, Any}(), Dict{Any, Any}(), false, false, [:index, :lev, :parent, :ncell, :peak_x, :peak_y, :peak_z, Symbol("rho-"), Symbol("rho+"), :rho_av, :mass_cl, :relevance], false, false, Symbol[], false, false), true, true, true, false, true, false, true, Dict{Any, Any}("&COOLING_PARAMS" => Dict{Any, Any}("cooling" => ".true. ", "metal" => ".true. ", "z_ave" => "1."), "&SF_PARAMS" => Dict{Any, Any}("m_star " => " 1. ! in units mass_sph", "n_star " => " 1 ", "T2_star" => " 1e4 ", "eps_star " => " 0.02 !2%"), "&AMR_PARAMS" => Dict{Any, Any}("levelmax" => "7", "npartmax" => " 500000", "ngridmax" => " 100000 ", "boxlen" => "100. !kpc\t", "levelmin" => "3 ", "nexpand" => "1                      "), "&BOUNDARY_PARAMS" => Dict{Any, Any}("jbound_min" => " 0, 0,-1,+1,-1,-1", "kbound_max" => " 0, 0, 0, 0,-1,+1", "no_inflow" => ".true.", "bound_type" => " 2, 2, 2, 2, 2, 2    !2", "nboundary " => " 6", "ibound_max" => "-1,+1,+1,+1,+1,+1", "ibound_min" => "-1,+1,-1,-1,-1,-1", "jbound_max" => " 0, 0,-1,+1,+1,+1", "kbound_min" => " 0, 0, 0, 0,-1,+1"), "&OUTPUT_PARAMS" => Dict{Any, Any}("tend" => "10                 !Final time of the simulation", "delta_tout" => "0.1          !Time increment between outputs"), "&POISSON_PARAMS" => Dict{Any, Any}("gravity_type" => "-3       "), "&UNITS_PARAMS" => Dict{Any, Any}("units_density " => " 0.677025430198932E-22 ! 1e9 Msol/kpc^3", "units_time    " => " 0.470430312423675E+15 ! G", "units_length  " => " 0.308567758128200E+22 ! kpc"), "&RUN_PARAMS" => Dict{Any, Any}("pic" => ".true.", "nsubcycle" => "20*2 ", "clumpfind" => "true", "ncontrol" => "1                      !frequency of screen output", "poisson" => ".true.", "verbose" => ".false.", "nremap" => "5 !10", "nrestart" => "99", "hydro" => ".true."), "&CLUMPFIND_PARAMS" => Dict{Any, Any}("ivar_clump" => "1", "density_threshold" => "0.01"), "&FEEDBACK_PARAMS" => Dict{Any, Any}("t_sne" => "10. !10. !Myr", "eta_sn " => "0.2", "!delayed_cooling" => ".true.", "!t_diss " => " 1.\t!Myr", "f_ek" => "0.")…), true, true, Mera.FilesContentType(["#############################################################################", "# If you have problems with this makefile, contact Romain.Teyssier@gmail.com", "#############################################################################", "# Compilation time parameters", "NVECTOR = 64 #32", "NDIM = 3", "NPRE = 8", "NVAR = 6", "NENER = 0", "SOLVER = hydro"  …  "\t\$(F90) \$(FFLAGS) -c write_patch.f90 -o \$@", "%.o:%.F", "\t\$(F90) \$(FFLAGS) -c \$^ -o \$@ \$(LIBS_OBJ)", "%.o:%.f90", "\t\$(F90) \$(FFLAGS) -c \$^ -o \$@ \$(LIBS_OBJ)", "FORCE:", "#############################################################################", "clean:", "\trm -f *.o *.\$(MOD) *.i", "#############################################################################"], [" --------------------------------------------------------------------", "", "     minimum       average       maximum  standard dev        std/av       %   rmn   rmx  TIMER", "       0.388         0.392         0.397         0.004         0.009     0.7     4   1    refine                  ", "       0.507         2.917         5.424         1.783         0.611     5.5     1   3    particles               ", "       1.347         1.701         2.269         0.344         0.202     3.2     4   1    feedback                ", "      16.465        17.380        18.250         0.646         0.037    32.7     3   1    poisson                 ", "       3.399         4.081         4.713         0.478         0.117     7.7     3   1    rho                     ", "       0.529         0.541         0.550         0.008         0.014     1.0     1   3    courant                 ", "       0.079         0.091         0.098         0.007         0.081     0.2     3   2    hydro - set unew        ", "      15.304        18.454        22.169         2.656         0.144    34.8     3   4    hydro - godunov         ", "       1.796         5.559         8.199         2.596         0.467    10.5     4   3    hydro - rev ghostzones  ", "       0.109         0.132         0.142         0.013         0.100     0.2     3   2    hydro - set uold        ", "       0.057         0.088         0.122         0.023         0.262     0.2     1   4    hydro upload fine       ", "       1.073         1.312         1.474         0.161         0.122     2.5     3   4    cooling                 ", "       0.112         0.122         0.135         0.009         0.078     0.2     4   3    hydro - ghostzones      ", "       0.298         0.301         0.306         0.003         0.011     0.6     4   1    flag                    ", "      53.074     100.0    TOTAL"], ["/data2/mabe/MeraTest/Ramses/patch_2019_10version/add_list.f90", "!################################################################", "!################################################################", "!################################################################", "!################################################################", "subroutine add_list(ind_part,list2,ok,np)", "  use amr_commons", "  use pm_commons", "  implicit none", "  integer::np"  …  "     end do", "", "  end do", "  ! 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A small helper to show a 2D map with physical axes and a colourbar (we will reuse it):

function showmap(M, ext_kpc; title="", clabel="log₁₀ Σ [M⊙/pc²]", logscale=true, cmap=:inferno, crange=nothing)
    A = logscale ? log10.(replace(M, 0.0=>NaN)) : Float64.(M)
    fig = Figure(size=(560,470))
    ax  = Axis(fig[1,1], aspect=DataAspect(), title=title, xlabel="x' [kpc]", ylabel="y' [kpc]")
    hm  = crange===nothing ?
        heatmap!(ax, range(ext_kpc[1],ext_kpc[2],length=size(A,1)), range(ext_kpc[3],ext_kpc[4],length=size(A,2)), A, colormap=cmap, nan_color=:black) :
        heatmap!(ax, range(ext_kpc[1],ext_kpc[2],length=size(A,1)), range(ext_kpc[3],ext_kpc[4],length=size(A,2)), A, colormap=cmap, nan_color=:black, colorrange=crange)
    Colorbar(fig[1,2], hm, label=clabel)
    fig
end

showmap (generic function with 1 method)

0. The camera basis

Every off-axis view is just an orthonormal camera basis built from the line of sight: w (the viewing direction), and right/up spanning the image plane (image x = right, y = up), right-handed with right × up = w. Each cell is carried along w onto that plane. Everything below only changes how this basis is pointed — the basis travels on the returned map (.los, .cam_right, .up, .center, .direction).

cam = projection(gas, :sd, :Msol_pc2; los=[0,0,1], center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
println("line of sight   w     = ", round.(cam.los, digits=3))
println("camera right (image x)= ", round.(cam.cam_right, digits=3))
println("camera up    (image y)= ", round.(cam.up, digits=3))
println("projection centre     = ", round.(cam.center, digits=3), "   direction = ", cam.direction)
showmap(cam.maps[:sd], cam.extent .* gas.scale.kpc; title="los=[0,0,1]  (image x→right, y→up)")

[Mera]: 2026-06-06T10:06:22.435



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = 

[0.0, 0.0, 1.0]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 344 x 344



line of sight   w     = 

[0.0, 0.0, 1.0]
camera right (image x)= [0.0, -1.0, 0.0]
camera up    (image y)= [1.0, 0.0, -0.0]
projection centre     = [0.5, 0.5, 0.5]   direction = offaxis

png

1. The everyday way: `inclination` & `azimuth`

Tilt the view away from a reference axis by inclination (0° = looking straight down the axis, 90° = perpendicular) and rotate around it by azimuth. Angles are in degrees.

axis defaults to the box :z (assumes nothing — good for clouds/filaments). For a disk use axis=:angmom (the object's own angular momentum L): then 0° = face-on, 90° = edge-on.

m = projection(gas, :sd, :Msol_pc2; inclination=60, azimuth=30, axis=:angmom,
               center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
showmap(m.maps[:sd], m.extent .* gas.scale.kpc; title="inclination 60°, azimuth 30°")

[Mera]: 2026-06-06T10:06:37.431



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.7427, -0.4216, -0.5202]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 473 x 533

png

Face-on → edge-on sequence

Only the camera changes; the data do not.

fig = Figure(size=(1500,420))
for (k,i) in enumerate((0,30,60,90))
    p = projection(gas, :sd, :Msol_pc2; inclination=i, axis=:angmom, binning=:overlap,
                   center=[:bc], range_unit=:kpc, pxsize=[0.3, :kpc])
    A = log10.(replace(p.maps[:sd], 0.0=>NaN)); e = p.extent .* gas.scale.kpc
    ax = Axis(fig[1,k], aspect=DataAspect(), title="i = $(i)°")
    heatmap!(ax, range(e[1],e[2],length=size(A,1)), range(e[3],e[4],length=size(A,2)), A, colormap=:inferno, nan_color=:black)
    hidedecorations!(ax)
end
fig

[Mera]: 2026-06-06T10:06:38.543



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [-0.0144, 0.0222, -0.9997]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 347 x 351



[Mera]: 2026-06-06T10:06:39.315



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 
Weighting      = :mass
Off-axis LOS   = [0.4875, 0.0193, -0.8729]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 469



[Mera]: 2026-06-06T10:06:39.706

center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.8588, 0.0114, -0.5123]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 474



[Mera]: 2026-06-06T10:06:40.241

center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.9999, 0.0003, -0.0143]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 353

png

2. Other ways to choose the view

Give exactly one line-of-sight specifier (two raise an error, so a wrong figure can't slip through). All are equivalent ways to point the camera:

option	meaning
`inclination`, `azimuth`, `axis`	tilt from a reference axis (recommended)
`direction=:faceon` / `:edgeon`	disk along / ⟂ to L (shortcut for `axis=:angmom`)
`los=[lx,ly,lz]`	explicit line-of-sight vector
`theta`, `phi`	spherical angles about the box axes

Modifiers: position_angle rolls the image about the line of sight; up=[..] sets the camera up.

!!! note :faceon/:edgeon/axis=:angmom use L, computed about center — center on the object so L is the true spin.

fo = projection(gas, :sd, :Msol_pc2, direction=:faceon, center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
showmap(fo.maps[:sd], fo.extent .* gas.scale.kpc; title="direction=:faceon")

[Mera]: 2026-06-06T10:06:42.029



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [-0.0144, 0.0222, -0.9997]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 347

png

# explicit vector + an image roll (position angle)
pr = projection(gas, :sd, :Msol_pc2, los=[1,1,1], position_angle=30, center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
showmap(pr.maps[:sd], pr.extent .* gas.scale.kpc; title="los=[1,1,1], position_angle=30°")

[Mera]: 2026-06-06T10:06:42.897



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.5774, 0.5774, 0.5774]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 552 x 482

png

3. Binning: how rotated cells land on pixels

Four deposit schemes (keyword binning): :overlap (the default — per-cell footprint supersampling, ns = ceil(cellsize/pixel) sub-points per cube axis capped at nmax=64; AMR-aligned, no moiré or holes, and usually faster than :exact), :exact (the analytic box-spline footprint — the line-of-sight column integrated per pixel, the fidelity reference), and two fast previews :cic (bilinear) / :ngp (nearest-pixel) that can speckle/moiré on coarse AMR cells. All four conserve the projected total. The quantitative accuracy study (holes, convergence) lives in notebook 13 — validation; here we contrast a fast preview (:cic) with the artifact-free default (:overlap) and the analytic reference (:exact) on the same view. Raise nmax for fewer artifacts on very coarse cells (slower, ∝ nmax³).

fig = Figure(size=(1500,440))
for (k,b) in enumerate((:cic, :overlap, :exact))
    p = projection(gas, :sd, :Msol_pc2; los=[1,1,1], binning=b, center=[:bc], range_unit=:kpc, pxsize=[0.3, :kpc])
    A = log10.(replace(p.maps[:sd], 0.0=>NaN))
    ax = Axis(fig[1,k], aspect=DataAspect(), title="binning = :$(b)"); hidedecorations!(ax)
    heatmap!(ax, A, colormap=:inferno, nan_color=:black)
end
fig

[Mera]: 2026-06-06T10:06:43.509

center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.5774, 0.5774, 0.5774]  (binning=:cic)
Effective resolution: 334^2  →  map size: 482 x 552

[Mera]: 2026-06-06T10:06:43.717



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 
Weighting      = :mass
Off-axis LOS   = [0.5774, 0.5774, 0.5774]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 482 x 552



[Mera]: 2026-06-06T10:06:44.172

center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd,) 


Weighting      = :mass
Off-axis LOS   = [0.5774, 0.5774, 0.5774]  (binning=:exact)
Effective resolution: 334^2  →  map size: 482 x 552

png

4. Gravity

The same view keywords drive the combined hydro+gravity interface — here the gravitational potential of the same galaxy, face-on.

grav = getgravity(info, lmax=gas.lmax, verbose=false, show_progress=false)
pe = projection(gas, grav, :epot; direction=:faceon, center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
showmap(pe.maps[:epot], pe.extent .* gas.scale.kpc; title="gravitational potential, face-on", clabel="Φ", logscale=false, cmap=:viridis)

  0.449511 seconds (1.62 M allocations: 165.754 MiB, 102.37% compilation time)
[Mera]: 2026-06-06T10:06:50.512



center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:epot, :sd) 


Weighting      = :mass
Off-axis LOS   = [-0.0144, 0.0222, -0.9997]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 347

png

5. Several quantities at once

One call returns a dictionary of 2D maps — here surface density, mass-weighted vₓ and temperature.

m = projection(gas, [:sd,:vx,:T], [:Msol_pc2,:km_s,:K]; inclination=35, axis=:angmom, center=[:bc], binning=:overlap, range_unit=:kpc, pxsize=[0.3, :kpc])
e = m.extent .* gas.scale.kpc; fig = Figure(size=(1450,440))
for (k,(v,cm,lab,lg)) in enumerate(((:sd,:inferno,"log₁₀ Σ",true),(:vx,:balance,"vₓ [km/s]",false),(:T,:viridis,"log₁₀ T",true)))
    A = lg ? log10.(replace(m.maps[v],0.0=>NaN)) : m.maps[v]
    ax = Axis(fig[1,2k-1], aspect=DataAspect(), title=String(v))
    hm = heatmap!(ax, range(e[1],e[2],length=size(A,1)), range(e[3],e[4],length=size(A,2)), A, colormap=cm, nan_color=:black)
    Colorbar(fig[1,2k], hm, label=lab); hidedecorations!(ax)
end
fig

[Mera]: 2026-06-06T10:06:52.080

center: [0.5, 0.5, 0.5] ==> [50.0 [kpc] :: 50.0 [kpc] :: 50.0 [kpc]]

domain:
xmin::xmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
ymin::ymax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]
zmin::zmax: 0.0 :: 1.0  	==> 0.0 [kpc] :: 100.0 [kpc]

Selected var(s)=(:sd, :vx, :T) 


Weighting      = :mass
Off-axis LOS   = [0.5618, 0.0183, -0.8271]  (binning=:overlap)
Effective resolution: 334^2  →  map size: 351 x 479

png

Play around

change inclination, azimuth, or set los=[...];
try axis=:z (box vertical) vs axis=:angmom (disk);
compare binning=:cic (fast preview) with the :overlap default at small pxsize, and raise nmax for very coarse cells;
the returned map stores the camera: m.los, m.up, m.cam_right, m.center, m.direction.

Next: LOS cubes & kinematics (12_multi_LosCubes) and validation (13_multi_OffAxis_Validation).