map_commands.rs and map_processor.rs — 3D Map Rendering & Coordinate Transforms

map_processor.rs + map_commands.rs — 3D Map Rendering & Coordinate Transforms

Converts 3D map files into top-down orthographic PNG images coloured by height (Z), and exposes coordinate transforms so the frontend can convert pixel clicks back to real-world metres. The pipeline runs on a blocking thread to avoid stalling the async runtime.

Supported formats

Extension	Library	Notes
.obj	tobj	OBJ Y-up convention remapped: world X = OBJ X, world Y = OBJ Z, height = OBJ Y
.las	las	X/Y/Z read directly from point records
.laz	las	Same as LAS (compressed)

Commands

render_map(filename) → MapMeta Renders a 3D map file to a top-down PNG. The source file must already exist in <appDataDir>/maps/. The output is written to the same directory as <stem>_preview.png. The image is sized to a 2048 px longest edge, aspect ratio preserved. Heavy work is offloaded via spawn_blocking so the async runtime is never blocked. Returns a MapMeta struct the frontend uses for pixel→world transforms.

pixel_to_world(px, py, meta) → (f64, f64) Converts a 2D pixel coordinate (origin bottom-left, X right, Y up) to real-world metres. Expects coordinates in the displayed image's frame — rotation, if any, must be accounted for by the frontend before calling this. The formula is simply world = pixel × metres_per_pixel, with the world origin anchored to the bottom-left corner of the image.

MapMeta fields

MapMeta is serialised and returned to the frontend after every render_map call.

Field	Type	Description
img_width	u32	PNG width in pixels (post-rotation)
img_height	u32	PNG height in pixels (post-rotation)
world_x_min	f64	Real-world X at the left edge (currently always 0.0 )
world_y_min	f64	Real-world Y at the bottom edge (currently always 0.0 )
metres_per_pixel	f64	Scale factor for pixel→world conversion
format	String	Source format detected ( "obj" , "las" , "laz" )
rotated	bool	true  if the image was rotated 90° to landscape

Rendering pipeline

process_map() runs the full pipeline in five stages:

1. Load — Parse the source file into a flat list of Point3D structs (x, y, z in world space).
2. Bounding box — Compute x_min/max, y_min/max, z_min/max over all points. World width and height must be non-zero or an error is returned.
3. Rasterise — Map each point to a pixel coordinate. Where multiple points land on the same pixel, keep the highest Z (i.e. the sky-facing surface wins). Pixel dimensions are derived from img_size (2048) with the aspect ratio preserved.
4. Gap fill — Run a two-pass nearest-neighbour distance transform (fill_gaps) to fill pixels that received no points. The forward pass sweeps top-left → bottom-right (checking left and top neighbours); the backward pass sweeps bottom-right → top-left (checking right and bottom neighbours). Each unfilled pixel inherits the Z of its closest filled neighbour, eliminating stripe artifacts.
5. Colour + save — Each pixel's Z is normalised to [0.0, 1.0] and passed through a five-stop colour ramp (height_color): deep blue → cyan → green → yellow → red. If all points share the same Z (flat terrain), mid-green is used. The image is rotated 90° if height exceeds width (to keep the longest edge horizontal), then saved as PNG.

Height colour ramp

Normalised Z	Colour
0.0	Deep blue
0.25	Cyan
0.5	Green
0.75	Yellow
1.0	Red

Error conditions

Condition	Error returned
Unsupported file extension	"Unsupported format: .{ext}"
File parsed but empty	"File parsed but contained no points."
All points collinear in X or Y	"All points are collinear — cannot build a 2D map."
Source file missing at invoke time	"File not found: {path}"
PNG write failure	"Failed to save PNG: {e}"