Background/Setup

• I have two physical 1TB disks with identical setup.
• Both are encrypted.
• I unlocked and booted off one of them.
• The other disk is still locked at this point.
• I am using fish shell.

1. Identify which disk you want to unlock

root@computer ~# lsblk -f
sda                                                                                                    
├─sda1                                        vfat              7F3B-9703                              /boot/efi
├─sda2                                        ext2              b6220db2-916c-4322-b64b-c86769f6b18b   /boot
└─sda3                                        crypto_LUKS       3a07b8a9-3e75-41a9-88d4-3be937181613   
  └─luks-3a07b8a9-3e75-41a9-88d4-3be937181613 LVM2_member       uCvHaW-RlQc-PT2d-cBg2-SWyY-WS0A-ZCEvA6 
    ├─ubuntu--vg-root                         ext4              a78662e2-d582-4faa-88b6-b6db5e23aed2   /
    └─ubuntu--vg-swap_1                       swap              5c4ba6cc-4735-4417-9e87-74a76a7fc415   [SWAP]
sdb                                                                                                    
├─sdb1                                        vfat              1EC8-1F58                              
├─sdb2                                        ext2              7108fe1d-dc37-4213-a3bc-8070a8f84f31   /media/jsun/7108fe1d-dc37-4213-a3bc-8070a8f84f31
└─sdb3                                        crypto_LUKS       fc560468-588c-4455-af2c-295998c41c88   

We see that sdb3 is the unmounted target.

2. Unlock the partition

root@computer ~# udisksctl unlock -b /dev/sdb3 
Passphrase:  
Unlocked /dev/sdb3 as /dev/dm-3.

See which one is the new unlocked

root@computer ~# ls -la /dev/mapper/ | grep dm-3 
lrwxrwxrwx  1 root root       7 Mar 22 17:32 luks-fc560468-588c-4455-af2c-295998c41c88 -> ../dm-3 

luks-fc560468-588c-4455-af2c-295998c41c88 is our target. Let’s remember that with a variable.

set target luks-fc560468-588c-4455-af2c-295998c41c88

3.

The VG Name of both drives is the same; this is problematic and will prevent you from being able to mount the drives both at the same time.

root@computer ~# pvdisplay
   --- Physical volume ---   
PV Name               /dev/mapper/luks-3a07b8a9-3e75-41a9-88d4-3be937181613   
VG Name               ubuntu-vg   PV Size               930.53 GiB / not usable 2.00 MiB   
Allocatable           yes (but full)   
PE Size               4.00 MiB   
Total PE              238216   
Free PE               0   
Allocated PE          238216   
PV UUID               uCvHaW-RlQc-PT2d-cBg2-SWyY-WS0A-ZCEvA6
       --- Physical volume ---   
PV Name               /dev/mapper/luks-fc560468-588c-4455-af2c-295998c41c88   
VG Name               ubuntu-vg   
PV Size               930.53 GiB / not usable 2.00 MiB   
Allocatable           yes (but full)   
PE Size               4.00 MiB   
Total PE              238216   
Free PE               0   
Allocated PE          238216   
PV UUID               lbvecI-E6w6-fpuj-P61G-5NCb-obOK-ooivpe

Get the uuid of the volume

root@computer ~# uuidgen
 1ec80451-b05b-4d59-94c1-f1ad70b24255
 root@computer ~# vgrename $uuid 1ec80451-b05b-4d59-94c1-f1ad70b24255
   Processing VG ubuntu-vg because of matching UUID TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v
   Volume group "TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v" successfully renamed to "1ec80451-b05b-4d59-94c1-f1ad70b24255"
 root@computer ~# pvs -o +vg_uuid
   PV                                                    VG                                   Fmt  Attr PSize   PFree VG UUID                               
   /dev/mapper/luks-3a07b8a9-3e75-41a9-88d4-3be937181613 ubuntu-vg                            lvm2 a--  930.53g    0  TAva2M-zNnV-Wh5h-3YcY-Vc5U-W4se-TI27Du
   /dev/mapper/luks-fc560468-588c-4455-af2c-295998c41c88 1ec80451-b05b-4d59-94c1-f1ad70b24255 lvm2 a--  930.53g    0  TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v

The device UUID is TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v. Let’s remember that with a variable.

set uuid TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v

Change the volume group

I’m going to generate a UUID, but you can name whatever you want.

root@computer ~# uuidgen
 1ec80451-b05b-4d59-94c1-f1ad70b24255
 root@computer ~# vgrename $uuid 1ec80451-b05b-4d59-94c1-f1ad70b24255
   Processing VG ubuntu-vg because of matching UUID TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v
   Volume group "TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v" successfully renamed to "1ec80451-b05b-4d59-94c1-f1ad70b24255"
 root@computer ~# pvs -o +vg_uuid
   PV                                                    VG                                   Fmt  Attr PSize   PFree VG UUID                               
   /dev/mapper/luks-3a07b8a9-3e75-41a9-88d4-3be937181613 ubuntu-vg                            lvm2 a--  930.53g    0  TAva2M-zNnV-Wh5h-3YcY-Vc5U-W4se-TI27Du
   /dev/mapper/luks-fc560468-588c-4455-af2c-295998c41c88 1ec80451-b05b-4d59-94c1-f1ad70b24255 lvm2 a--  930.53g    0  TJgeFw-xDcf-TaJ2-07dL-RlUQ-yCsb-zGGp4v

Check/notice the new volume group name 1ec80451-b05b-4d59-94c1-f1ad70b24255.

Confirm the change

root@computer ~# vgchange -a y
   2 logical volume(s) in volume group "ubuntu-vg" now active
   2 logical volume(s) in volume group "1ec80451-b05b-4d59-94c1-f1ad70b24255" now active

Remember to rename your volume group back to ubuntu-vg if you want the volume to still be bootable.

Mount

root@computer ~# mkdir /media/badboy
 root@computer ~# mount /dev/1ec80451-b05b-4d59-94c1-f1ad70b24255/root /media/badboy
 root@computer ~# cd /media/badboy/
 root@computer /m/badboy# ls
 bin/   cdrom/  etc/   initrd.img@      lib/    lib64/       media/  opt/   root/  sbin/  srv/  tmp/  var/
 boot/  dev/    home/  initrd.img.old@  lib32/  lost+found/  mnt/    proc/  run/   snap/  sys/  usr/  vmlinuz@

You can now access your data.

EPT format is a storage method for point clouds, base on an octree structure. The encoding of the point cloud is up to the user, whether las/laz, binary, or whatever custom format. So let’s say you store it in laz. What EPT does is to generate the octree to manage how those laz files are stored.

Merging EPT

Given two geographically separated point clouds, it is possible to merge them into the same EPT structure, given they use the same frame of reference. Because Potree doesn’t handle latitude and longitude rendering (as they are angles and not euclidean), you have to use euclidean systems, such as UTM coordinates.

You must first specify a large bounds for the initial build, and add more files later like this:

entwine build -i ~/data/xyz -o ~/entwine/xyz -b "[100, 100, 0, 400, 400, 200]"
entwine build -i ~/data/abc -o ~/entwine/xyz

See Entwine issue 109

Caveats

A caveat is that when you’re generating the first frame, you need to custom input the bounding cube bounds, because by EPT design the octree cannot be rebalanced (without recomputing for all points).

Another caveat is that UTM zone is not encoded in the laz file, using UTM cannot be extended over geographical regions. Thus we may have to store xyz points in lat/lng/alt format.

Yet another caveat is the source ID for these points are going to collide. E.g. in file1.laz you have frames ID 0-100 and file2.laz you have frames ID 0-10, then the 0-10 IDs would collide. A workaround would be to assign global unique IDs.

The Western Digital (WD) Easystore 8TB is an external hard drive sold exclusively by Best Buy. It’s highly sought after because it contains a WD Red or unlabelled WD White 8TB drive, which can be “shucked” and used in a home server.

Typically you can get 8TB for $140+tax when on sale, whereas a regular WD 8TB NAS drive costs around $260+tax.

There are more details in this reddit post about the drives and how to shuck them.

After a few hours the volume is expanded.

The new C++17 language requires g++ >= 8.0. To install it in Ubuntu 18.04:

$ sudo apt install g++-8
...
$ which g++
/usr/bin/g++
$ which g++-8
/usr/bin/g++-8
$ sudo unlink g++
$ sudo link -s /usr/bin/g++-8 /usr/bin/g++
$ g++ --version
g++ (Ubuntu 8.2.0-1ubuntu2~18.04) 8.2.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

QGIS is a user friendly Open Source Geographic Information System (GIS).

sudo add-apt-repository ppa:ubuntugis/ppa
sudo apt install qgis