compare_octrees: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/compare_octrees - from package: octomap

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/compare_octrees - from package: octomap-tools

You may install the required package with command apt-get install {package}

Error in other languages:
compare_octrees: bevel nie gevind nie
compare_octrees: comandă negăsită
compare_octrees: comando não encontrado
compare_octrees: commande introuvable
compare_octrees: command not found
compare_octrees: käsku ei ole
compare_octrees: không tìm thấy lệnh
compare_octrees: komanda nerasta
compare_octrees: Kommando nicht gefunden.
compare_octrees: kommandot finns inte
compare_octrees: komut yok
compare_octrees: nie znaleziono polecenia
compare_octrees: níor aimsíodh an t-ordú
compare_octrees: no se encontró la orden
compare_octrees: no s'ha trobat l'ordre
compare_octrees: opdracht niet gevonden
compare_octrees: parancs nem található
compare_octrees: perintah tidak ditemukan
compare_octrees: príkaz nenájdený
compare_octrees: příkaz nenalezen
compare_octrees: команда не найдена
compare_octrees: командата не е открита
compare_octrees: 命令找不到
compare_octrees: コマンドが見つかりません