Category: Tech&Science

Technical stuff

GPS Accuracy of the Garmin Flagships

by jorgen on 2025-02-14 in Navigation, Tech&Science

As a kid I fantasized about how great it would be to have a map on which you could see where you are, like the Marauders Map of Harry Potter. Who could have thought that a couple of years later there would be a technology that makes it possible, a technology so brilliant that it even takes into account Einsteins’ special theory of relativity.

Since my first GPS I am always looking for the most accurate GPS for logging my sports and hiking trips. I started in 2007 with the Garmin GPSMAP 60csx, but it was quite bulky for running (I had to keep it in hand). I therefore switched to the relatively unknown I-gotU devices. They were succeeded by the TomTom weareables (Adventurer) and they seemed pretty accurate (I still use them for open water swimming, attached to my buoy). Since they were discontinued I switched to Garmin. On my bike I have used the Edge 810, Edge 830 and am currently using the Edge 1040. For running and swimming the Fenix 7 and for hiking I recently bought the GPSMAP 67. The latter 3 are currently the top-of-the-bill consumer models from Garmin that use multiple satellite systems.

I’ve been using the Fenix 7 and Edge 1040 for quite some time now and they are giving good results and good agreement if I use them both (and I often do). I expected the GPSMAP67 to perform at least as good as them, if not better, since it has the same GPS chip, but a better antenna. So I took all three of them on a MTB trip through the forest. Auch! The result of the GPSMAP 67 was a bit disappointing: it’s track deviated from the Fenix 7 and Edge 1040 tracks. Though the Fenix and Edge are in good agreement with each other throughout the entire trip, the GPSMAP 67 showed deviations. And yes, two against one…

Red: Edge 1040, Blue: Fenix 7, Green: GPSMAP 67. Deviations from left to right (thin line): 12 m, 19 m, 11 m and 8 m.

Reason to put them on the test bench for a more thorough examination…

Disclaimer: yes, I am a GPS weirdo 🤪and I go to the last cm. If you think: ‘Man, what are you fuzzing about?‘, stop reading here.

Important notice: during testing I found a serious issue on the GPSMAP 67 on which I reported in another post. Due to this issue the GPSMAP67 is unreliable because it might show your location with a large error. I reported it to Garmin Support but they don’t take it seriously and just refer to their FAQ.

KeePass, Keeweb with OneDrive and Dropbox

by jorgen on 2023-01-11 in Tech&Science

Introduction

This blog describes some hints to get a self hosted Keeweb working with a KeePass database files stored on Microsoft OneDrive or Dropbox.

KeePass is an open source password manager. It is a PC application storing your credentials and secrets in an encrypted .kdbx database file. I use it for some time now and I am happy with it. I started to use it with my database on a memory stick, to have it anywhere I go. This, however, is not a fine way of working, because I tend to forget my memory stick. So I wondered if I could use my KeePass database in a self hosted web based application. I did some searching around and found Keeweb to be most applicable.

Keeweb comes in a desktop application as well as a web application. The latter seems to be about what I want.

However, I like to be in control and host the application myself. I finally succeeded to get it working with my KeePass database on Microsoft OneDrive and and on Dropbox. There are two sites I would like to mention that provide a howto.

Host Your Own Multi-User Password Manager with KeeWeb and WebDAV
Dropbox and GDrive, which also explains Microsoft OneDrive

Why then, this blog as third howto? Well, following both links still gave me some head-aches. Therefore I report my findings

Open Sesamy: Port-knocking using just one port

by jorgen on 2014-05-02 in Tech&Science

Port knocking is a mechanism to provide additional security to firewalling. Port knocking is normally used in firewalls. A target port needed for a particular service (e.g. SecureShell, SSH) is normally closed and the service is unreachable. Only by ‘knocking’ on a number of ports in a particular order opens the target port. Knocking means: sending a TCP or UDP packet to the port. Though the knock ports are closed and won’t respond, the firewall notices the knocks. To the outside world the firewall appears totally closed. Portscans fail. Only when the proper sequence of ports is knocked the target port opens and the service is reachable for a few seconds. During this time-span the service can be reached.

There are a large number of port knock implementation. See for an overview: portknocking.org. Open Sesamy differs from other mechanism because only one port for knocking is needed. It may even be the target port. It is implemented using Linux iptables. This is another difference: most port knocking algorithms are implemented as scripts scrutenising the log files. Using iptables the packet filtering is exploited as present in the Linux kernel or modules.