celibistrial

Generalizing a LiDAR localizer to ridiculous extents

Sat, 26 Sep 2026 00:00:00 +0000

You have been kidnapped and dropped into a random warehouse. All you get is one look around and a map of the building with no colour on it. Can you tell where you are?

That was eternal.ag’s challenge at TechQuest, a new two-week hackathon at IIT Patna. A robot is dropped somewhere in a building. You get one 360° LiDAR sweep (a 32-beam laser scanner that returns a cloud of 3D points), one camera frame, and a point cloud of the building with geometry only, no colour. There’s no GPS and no starting guess. You output the robot’s full 6-DoF pose.

Fastest lock screen using i3lock

Mon, 01 Jan 2024 00:00:00 +0000

This script takes a screenshot of your desktop, blurs it, and locks the screen with the blurred image as the background. The whole thing runs in under a second.

You need scrot, ImageMagick (for convert), and i3lock.

#!/bin/bash
PICTURE=/tmp/i3lock.jpg

scrot --silent "$PICTURE"
convert -scale 10% -blur 0x0.5 -resize 1000% "$PICTURE" "$PICTURE"
pkill i3lock
i3lock -i "$PICTURE"
rm "$PICTURE"

How it works

scrot saves a screenshot to /tmp/i3lock.jpg.

The convert line does the blur. Shrinking the image to 10% and scaling it back up by 1000% throws away most of the detail, which gives the pixelated look, and -blur 0x0.5 softens the blocky edges a little. This is much faster than a real Gaussian blur on a full-size screenshot, and it’s the reason the script is quick.

Making highlight.js work with org-export

Mon, 01 Jan 2024 00:00:00 +0000

Org-mode can export to HTML, PDF and LaTeX, but its HTML export doesn’t highlight code blocks, which makes code hard to read. highlight.js fixes that. It’s a JavaScript syntax highlighter that works on almost any markup, doesn’t depend on other frameworks, and detects the language on its own.

This post assumes you’ve already set up org-publish-project-alist to export your .org files to .html. We’ll change that variable to load highlight.js.

Modifying org-publish-project-alist

Your org-publish-project-alist probably looks something like this:

Publishing beautiful html pages with org

Mon, 01 Jan 2024 00:00:00 +0000

Org’s HTML export works, but the pages it produces look plain. The fix is your own CSS, and this snippet lets you keep a folder of CSS themes and choose one each time you export.

Setup

Put your CSS files in ~/.emacs.d/org-css/, or change org-theme-css-dir to wherever you keep them.
Run toggle-org-custom-inline-style in an org buffer that’s visiting a file.
Export to HTML with C-c C-e. Emacs now asks which theme to use.

The snippet

;; put your css files there
(defvar org-theme-css-dir "~/.emacs.d/org-css/")

(defun toggle-org-custom-inline-style ()
 (interactive)
 (let ((hook 'org-export-before-parsing-hook)
 (fun 'set-org-html-style))
 (if (memq fun (eval hook))
 (progn
 (remove-hook hook fun 'buffer-local)
 (message "Removed %s from %s" (symbol-name fun) (symbol-name hook)))
 (add-hook hook fun nil 'buffer-local)
 (message "Added %s to %s" (symbol-name fun) (symbol-name hook)))))

(defun org-theme ()
 (interactive)
 (let* ((cssdir org-theme-css-dir)
 (css-choices (directory-files cssdir nil ".css$"))
 (css (completing-read "theme: " css-choices nil t)))
 (concat cssdir css)))

(defun set-org-html-style (&optional backend)
 (interactive)
 (when (or (null backend) (eq backend 'html))
 (let ((f (or (and (boundp 'org-theme-css) org-theme-css) (org-theme))))
 (if (file-exists-p f)
 (progn
 (set (make-local-variable 'org-theme-css) f)
 (set (make-local-variable 'org-html-head)
 (with-temp-buffer
 (insert "<style type=\"text/css\">\n<!--/*--><![CDATA[/*><!--*/\n")
 (insert-file-contents f)
 (goto-char (point-max))
 (insert "\n/*]]>*/-->\n</style>\n")
 (buffer-string)))
 (set (make-local-variable 'org-html-head-include-default-style)
 nil)
 (message "Set custom style from %s" f))
 (message "Custom header file %s doesnt exist")))))

How it works

toggle-org-custom-inline-style adds set-org-html-style to the export hook for the current buffer, and running it again removes it. When you export, set-org-html-style asks you to pick a CSS file from the folder and pastes its contents into a <style> tag in the page head. It also turns off org’s default styles, so they don’t fight with your theme.

About me

Mon, 01 Jan 0001 00:00:00 +0000

Hi, I’m Gaurav, I build (useful??) things and write about the peculiar.