Matt,

For some strange reason I can not add the manual water level 0.58 and 0.57 m.
I have tried a number of other values, and they all worked, but there might of course be others still that do not work.

//Mats

Hi Mats,
Feet or metres? Might be a rounding issue - I will investigate.
thanks,
Matt

Edit: these round to 1 decimal place, so I get 0.6 when I enter either of the values you mention. This is when using metres. Perhaps that could be 2 DP for metres, although I'm not sure if there would be any real-world benefit in a sub 10cm resolution?

metres,thats what the "m" stands for ;-))

:) I edited my post whilst you replied - values just round to 0.6m for me. Do you get different behaviour?

There is a bit of a gotcha with the "water level" feature (described in more detail the manual). The feature is actually just a short-hand way of entering a single tide point, which is then used in the same way as a tide offset. If there is already more than one tide point for a track, the water level feature is disabled. I'm not sure that this could be causing your issue though - it would not be value dependent.

Strange, because I get a two decimal value. So when I enter 0.58 then I get 0.57, as shown in the screenshot below:

It's very improbable, that such a high accuracy make sense.

neither the accuracy of the GPS recipient, nor a cm-exact-depth logg is possible in the practice.
Rounding is more applicable, or You a scientist with high tech equipment e. g. more as dGPS?

Fjordfisher,

I can agree that the practical use of 1 cm resolution can be questioned. But as an engineer, one tends to use the best data at hand. And I can easily read the water level with 1 cm resolution, so why not use it?!

The GPS accuracy does not really matter in this case since the water level affects the whole lake. But since I work with AIS and Navigation systems, I find it an interesting subject. I have actually had plans to use dual DGPS in order to get higer precision and heading, but I don't think Lowrance support this today. You would need to build an external system for this first. Or buy the Hemisphere V100 or similar. On the other hand, considering the cost, I find the built in SIRF receiver in the HDS to be good enough for this application.

//Mats

Hello Mats,


OK, If You work as an Ingenieur - it's okay. The question of GPS in mm ... cm range is detachable.

The water depth is more in question with "normal" Lowrance or Airmar ducer equipment.

What You see is a depth interpolation, not the 100 % exact depth. The error would be greater, the deeper You logg. You would need a very small cone, 100 % vertical work on water with waves ... much expensive equipment.


Best wishes
fjordfisher

Mats,
I believe the value is actually stored to 2DP, but the display in the water level entry field is limited to 1DP. I'll double check this when I get the time..

Matt

Oh,

i also get cm values from an tide station in my local area in a 15 Minute period.
So if possible, i appreciate it if i can use these values with the accuracy they deliver.

If RM rounds up to always 10 cm up or down...
this brings poor accuracy.

Lets see the case of the rounding Point,
in the first 15 Minutes i have 1.44 Meters, then RM makes 1.4 Meters.
And in the next 15 Minutes i get 1.45 then RM makes 1.5 Meters.
Means i got a step of 10 cm from the first 15 Minutes to the last 15 Minutes.
Is this right ?

Or did i am gonna away from the topic and misunderstood something ?

No - internally the resolution is 1cm, and this problem only affects the display of the value in the "water level offset" field. In fact, if the value 1.56 is entered even in that field, the value will be retained internally - but 1.6 will be displayed. For interpolation between tide points, the resolution is is not limited in any way.

COOL !!
That sounds good.