I was wondering if it is possible to graph a lake in sections. If a lake is so large that one could not cover the whole thing in one outing, can sections be traversed and processed, and then the sections be "put together" as each one is completed, and imported into my unit?

Thanks very much for your help!!
ed

Hi Ed,
Maps can be made from any number of individual track-logs; each time you record a new track, just import it and add it to your project and re-generate the map. The new data will be incorporated. We have users making individual maps 15km (10 miles, more or less) across, using over 400 tracks. That is at the upper limit of what ReefMaster can support, and map generating will take a while for maps that large. You'll also need to be running 64 bit Windows with a decent amount of memory to make maps as big as that in one go.
If you need even bigger maps, then you can create multiple map projects. Contours from multiple map projects can be combined into a single user map and exported from there. It is also possible when exporting AT5 maps to just create multiple separate map files. So long as you rename these so that the filenames do not clash (keeping the original extensions), then the unit will load all maps present on the memory card.

Matt

I have been mapping lakes in sections. Our lakes here change in water level daily and up to 10-20 feet. how do u compensate for this when merging maps together.

I know the lake level of every map section i have done. do u just make up the distance to the full water mark and put that number in the manual tide location.

eg full level is 1000ft, day one i scan the map at water level 900ft i put 100 in the manual tide box.
Day two i scan the lake at 950ft so I put 50ft in the manual tide box ?

Yes - choose a reference depth, and then apply offsets as required to each track to bring it to that depth. Bear in mind that positive tide values are subtracted from the recorded depth - typically when tide adjusting, mean low water would be the reference depth, and positive tide values are subtracted from the recorded depth to create a map that reflects MLW. If you want to adjust your values to a value higher than the recorded depths, (your 950 - 1000 example) then you need to use negative tide offset values.

In the track edit panel, use the Manual tide option and just enter a single value for the depth. The time of the point is not important when using a single value; the same value will be used for all track-points within the track.

Matt

so i would enter -50 ?

If you are using a reference depth of 1000ft, and the current lake level is 950ft, then yes - you would enter -50 in the manual tide setting. Make sure you are running RM in feet, not metric (global settings).

Just a thought,

if your lake is varying by up to 20ft a day then it's varying considerably (probably linearly though) during your survey period. For lakes of substantial depth it may be of little consequence, for lakes with shallows, or lakes you want to chart accurately this variation during survey would need to be accounted for.
It may be better to split your tracklogs into 30 minute sections and adjust each individually. You certainly need to be recording the depth on departure and arrival though.

I'd suggest doing what we call a calibration run. This is simply a good run round the entire lake, at known level, against which you can calibrate subsequent intersecting surveys. You may need 2 or 3 of these calibration runs, and as you build up mapping surveys you can then use them as calibration surveys for subsequent surveys.

Sounds like an interesting lake !

T

Just to add to what Trevor said, if the lake is varying throughout the course of the day you can also use multiple tide points when adjusting the track level. If the movement is constant, you can enter the known offset at the beginning of the track and the known offset at the end, and points in between will be adjusted by a depth calculated by interpolating between these values. Generally, though, it is a good idea anyway to use multiple, short tracks - this also helps mitigate against losing data due to corruption of a single track etc.

Thanks for all your reply's. the dam levels are fairly stable during the day when i have the boat on it, its usually over night the level changes. Dams are for Hydro Electricity generation. I do have access to accurate dam level data.

Thank you