Garmin Etrex 20 waypoints on card?

[fhills]

Yes I know I could experiment/suck it and see (usually the best approach and if you want to learn stuff and have it stick in your mind) but to save me doing lots of backups in case I screw things up I thought it best to ask you knowledgeable folk.

The issue.

I have an Etrex 20 with lots and lots of waypoints and routes on it.

It very often gets close to 100 per cent.

Waypoints saved on the Garmin all seem to go onto the internal memory, meaning that a big card* is of no great use in that respect.

I recently obtained an Etrex20x which has more (double from memory) internal memory but was somewhat peturbed, to say the least, to see that on transferring the Etrex20's waypoints over to its internal memory I still got the same percentage full reading! So I assume that Garmin in its infinite wisdom has limited the area of the internal memory that can be used for such things.

So, while accepting that the Etrex20 will only write waypoints to internal memory, can I get it to READ them from both internal memory and the card? And without getting all confused/screwed up?

For if so I could clearly now and again take all of the waypoints off the Garmin's internal memory and puts some of them back on the internal memory and some on the card. Or even all on the card.

Views?
Exeriences?

* A big card is also of limited bleedin use as I also gather that the Garmin core unit has issues if you try to put too many separate maps on that card. Even if there's plenty of room. And maybe also if you disable one. Something to do with multiple datasets for the same area possibly?

[Bolt]

The capacity to store waypoints is based on a maximum of 2000 rather than available memory. 

Storage limits for the etrex20/30 are:

o   2,000 GPX files
o   2,000 waypoints
o   5,000 geocaches
o   200 routes, 250 points per route
o   200 saved tracks
o   2,000 archive tracks
o   10,000 points per track
o   100 custom map tiles
o   250 BirdsEye Imagery files
o   Approximately 3,000 mapping segments

[Kim]

It should be able to read waypoints/tracks/routes from GPX files on the card; you'll need a Garmin/GPX/ directory to put them in, and it should Just Work.

Note that there's a hard limit on the number of waypoints (presumably because they all have to be held in memory^[1] to work out whether to draw them on the map) regardless of whether there's space on the filesystem to store them, so moving waypoints to the card may not gain you anything.


_{[1] I'm using 'memory' in the technical sense, to mean RAM, rather than storage.  People seem to have forgotten the difference since floppy disks went out of fashion.}

[Kim]

o   2,000 waypoints
o   5,000 geocaches

Hmm, I've never used the geocaching features....could they be used as extra waypoints?

[fhills]

Note that there's a hard limit on the number of waypoints (presumably because they all have to be held in memory^[1] to work out whether to draw them on the map) regardless of whether there's space on the filesystem to store them, so moving waypoints to the card may not gain you anything.


_{[1] I'm using 'memory' in the technical sense, to mean RAM, rather than storage.  People seem to have forgotten the difference since floppy disks went out of fashion.}

If Garmin does chuck them all into memory that seems daft. Why couldn't they just be kept in storage and just called up if you had the area on screen/the GPS knew that you were within a certain distance of them?

Note am not saying you are wrong/daft - just pondering whether Garmin is daft.

[Kim]

If Garmin does chuck them all into memory that seems daft. Why couldn't they just be kept in storage and just called up if you had the area on screen/the GPS knew that you were within a certain distance of them?

Think about it.... You're at position $foo, and there's a bunch of waypoints in an XML file on disk.  In order to work out if you're near one you have to either:

Open the file, find the first waypoint, read it into memory.
Compare the locations.
Do something or not, according to distance.
Read the next waypoint from the file into memory.
Compare the locations.
Do something or not, according to distance.
(repeat until end of file)
Get on with refreshing the display etc. and all the other stuff you're supposed to be doing.


Alternatively:
On bootup, open the file, iterate through it reading each location and identifier into some data structure in memory.
...
Then you can:
Compare the locations.
Do something or not, according to distance.
Compare the next location.
Do something or not, according to distance.
(repeat until last waypoint)
Get on with all the other stuff.

(Obviously this is a handwaving simplification.)

RAM is fast and always on.  Storage access is slow, and probably means extra power draw.  So it's basically a tradeoff between speed and memory use.  You can throw a faster computer (and flash storage) at the problem, but that's expensive and you're likely to need more electricity.  Better to give it enough RAM for an arbitrary number of waypoints etc, and set some limit so you don't run out of memory for important things like the stack.  Then it becomes a tradeoff between cost of RAM and waypoint limit.  How many waypoints do Marketing reckon 90% of your potential customers care about?

[fhills]

thanks for the correction kim

[Kim]

Computer Science innit.  People like to pretend it's about clever algorithms, but the overwhelming majority of the time it's identifying what particular operation is the resource hog and trying to avoid doing it.