Other

Logarithm is the inverse operation to exponentiation

29 August 2017 in Funny / Other tagged LogaN / logarithm / math is fun by Tux

In mathematics, the logarithm is the inverse operation to exponentiation, just as division is the inverse of multiplication and vice versa. That means the logarithm of a number is the exponent to which another fixed number, the base, must be raised to produce that number. In the most simple case the logarithm counts repeated multiplication of the same factor; e.g., since 1000 = 10 × 10 × 10 = 10³, the “logarithm to base 10” of 1000 is 3. More generally, exponentiation allows any positive real number to be raised to any real power, always producing a positive result, so the logarithm can be calculated for any two positive real numbers b and x where b is not equal to 1. The logarithm of x to base b, denoted log_b (x) (or log_b x when no confusion is possible), is the unique real number y such that b^y = x. For example, log₂ 64 = 6, as 64 = 2⁶.

From: https://en.wikipedia.org/wiki/Logarithm

Another example: When N = a^x then x is equal to log_a (N) (or log_a N).
Comic is based on: https://www.facebook.com/cutbu2/photos/a.146307418902007.1073741874.145016865697729/479097838956295/

Regular expression to match any ASCII character

8 July 2017 in GNU/Linux / Other tagged ascii / characters / ignore all / match all / regex / regular expression by Tux

The following regular expression will match any ASCII character (character values [0-127]).

[\x00-\x7F]

The next regular expression makes the exact opposite match, it will match any character that is NOT ASCII (character values greater than 127).

[^\x00-\x7F]

gEdit – regular expression to match any ASCII character

gEdit – regular expression to match any Non-ASCII character

Facebook gives hints about what a picture contains on the ‘alt’ field

24 June 2017 in Other tagged computer vision / facebook / image processing / intelligent systems / machine vision by Tux

Just a fun fact:

Facebook posts some of the information that it automatically derives from user pictures in the alt field of the pictures.
Below we post two samples from a stream that demonstrating this feature:

In the first one we can read in the alt the following Image may contain: 1 person, smiling, closeup.

In the second one we can read in the alt the following Image may contain: 1 person, sitting, pool, sky and outdoor.

We can see that in both cases the information is pretty much valid.

Rough notes for DJI Phantom 2 Vision +

22 February 2017 in Other tagged DJI / DJI Phantom 2 Vision + / Phantom / Phantom 2 / Phantom 2 Vision + by Tux

After you connect to the Wi-Fi hot spot of the device (SSID: Phantom_XXXXXX):

System 1

ssh [email protected]
#Password for root is 19881209
[email protected]'s password: 


BusyBox v1.19.4 (2013-04-22 22:41:57 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

 -----------------------------------------------------
 DJI-INNOVATIONS
 -----------------------------------------------------
  * FC200-Vision+        
  * [email protected]
  * 02/20/2014
  * Version 1.01
  * ART / DHCP down / ping
 -----------------------------------------------------

System is based on OpenWrt.

System 2

ssh [email protected]
#Password for root is 19881209
[email protected]'s password: 


BusyBox v1.19.4 (2013-04-22 22:41:57 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

 -----------------------------------------------------
 DJI-INNOVATIONS
 -----------------------------------------------------
  * FC200-Vision+ RE   
  * [email protected]
  * 02/21/2014
  * Version 1.01
  * ART / DHCP down / ping
 -----------------------------------------------------

ssh -L 8080:downloads.openwrt.org:80 [email protected]

cat /etc/opkg.conf 
src/gz barrier_breaker http://downloads.openwrt.org/snapshots/trunk/ar71xx/packages
dest root /
dest ram /tmp
lists_dir ext /var/opkg-lists
option overlay_root /overlay

cat /etc/opkg.conf 
src/gz barrier_breaker http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/packages/base
dest root /
dest ram /tmp
lists_dir ext /var/opkg-lists
option overlay_root /overlay
option http_proxy http://127.0.0.1:8080/

root@Phantom:~# opkg update
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/packages/base/Packages.gz.
Updated list of available packages in /var/opkg-lists/barrier_breaker.
root@Phantom:~# opkg install tcpdump-mini
Installing tcpdump-mini (4.5.1-4) to root...
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/packages/base/tcpdump-mini_4.5.1-4_ar71xx.ipk.
Installing libpcap (1.5.3-1) to root...
Downloading http://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/packages/base/libpcap_1.5.3-1_ar71xx.ipk.
Configuring libpcap.
Configuring tcpdump-mini.




BAD TRUNC
opkg install tcpdump-mini
Installing tcpdump-mini (4.5.1-4) to root...
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/base/tcpdump-mini_4.5.1-4_ar71xx.ipk.
Installing libpcap (1.7.4-1) to root...
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/base/libpcap_1.7.4-1_ar71xx.ipk.
Configuring libpcap.
//usr/lib/opkg/info/libpcap.postinst: line 4: default_postinst: not found
Configuring tcpdump-mini.
//usr/lib/opkg/info/tcpdump-mini.postinst: line 4: default_postinst: not found
Collected errors:
 * pkg_run_script: package "libpcap" postinst script returned status 127.
 * opkg_configure: libpcap.postinst returned 127.
 * pkg_run_script: package "tcpdump-mini" postinst script returned status 127.
 * opkg_configure: tcpdump-mini.postinst returned 127.


From host machine:
ssh [email protected] tcpdump -i br-lan -s0 -w - port not 22 > dji-wifi-traffic.pcap

ssh [email protected] tcpdump -n -i br-lan -s0 -w - port 2001 > dji.2001.pcap


ip.src==192.168.1.1 || ip.dst==192.168.1.1 ||ip.src==192.168.1.2 || ip.dst==192.168.1.2 || ip.src==192.168.1.10 || ip.dst==192.168.1.10