Friday, 3 April 2015

The New GPS's

I mentioned a few posts ago that we had purchased two new GPS units.

The first GPS is a Mr Lee's Cat Track 1. This is much like our original GPS, however its an upgraded version.  Nigel spent quite a bit of time swearing at the computer trying to figure out how to download .gpx files. If you use this device as advertised, it returns data that looks like this

We however have been extracting the raw data and analysing it in QGIS.

In order to test the new GPS for accuracy, we strapped it to a bike and rode around the block, which returned surprisingly accurate data, leading us to believe that HDOP wasn't a great estimate of accuracy afterall.  Although its also worth noting that precision is dependant on the number of satellites the GPS can access to triangulate the position.  A bike riding down an open road is going to get easier exposure to satellites than a cat skulking around under houses, sheds and through the undergrowth.

So we've filtered by the number of satellites rather than HDOP on this occasion to determine accuracy.  As discussed in the previous post, Bento, the newest kitten, isn't travelling far from the house at all.

The second GPS we purchased is a G-Paws Track, this unit is smaller than the Mr Lee unit and easier to extract the data from. There is an option to log into the G-Paws website and simply upload the data into a webpage. However, you can also simply plug it into your computer and it shows up as a flash drive with .gpx files on it. 

The downside is that the .gpx data is less verbose than the Mr Lee unit, it doesn't contain any HDOP/VDOP data or number of satellites used data.  However, the upside is that it appears much more accurate than the the Mr Lee unit.  Its also a smaller unit, so despite the slightly higher price tag, it seems the better GPS.

Here is a photo of Corsair being unco-operative and modelling the GPS.

The map below shows Magellan's wandering for the last couple of weeks. This data is unfiltered.

This data shows that Magellan is travelling no more than about 70m from the house.  This is is a bit different than results gained from the Mr Lee Unit.  This earlier post shows Magellan travelling upto 150m from the house and spending more time on the other side of the street, this time he is sticking to our side of the street. Its worth noting that there is a years worth of time between the data collection, and Magellan has broken his leg in that time, although he does appear to have made a full recovery.

I'm going to break Magellan's wandering down in more detail in my next post.

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