Question on a crazy idea

[pyrodogg]

I've just discovered this site and it's got me thinking...

I'm taking a trip to Lake Powell in a few weeks.  Being that it's a reservoir, the lake level is almost constantly changing (for the past month a 1 foot increase per day).  Maps that i've seen are usually generated for a full pool lake level.

Would it be possible to generate maps based on a lake level you could specify at compile time? Or easily precompile maps based on a range of lake levels?

I currently have no experience in map making but I am a programmer. So, if this is possible it's something i'm interested in throwing some time at.   Any tips would be most appreciated.

Thanks.

[Seldom]

I don't have any experience with marine maps, but assuming depth contours and land contours are similar the depth indication is a text label associated with the polyline.  In the MP code sample below the label represents 4760 feet above sea level, the Data0 line is the list of lat and lon points describing the polyline, Type 0x20 denotes a minor land contour and the Endlevel denotes the zoom level beyond which it disappears.  

If the depth changes, you'll need a way to change the label to the revised depth.   This is probably done more easily by manipulating the shapefile database you'll probably be using and exporting the shapefile to MP format, or compiling the shapefile with cgpsmapper.  

Code Select Expand

[POLYLINE]
Type=0x20
Label=4760
EndLevel=3
Data0=(38.33069,-111.00000),(38.33057,-111.00013),(38.33050,-111.00032),(38.33042,-111.00000)
[END]

Finding bathymetry will be your main problem.  If you are lucky, it will be in shapefile format.
Others here, Boyd particularly, may be able to tell you more about how to manipulate the shapefile database.

[Boyd]

Have not tried that, but Filemaker Pro can do just about anything you want with .dbf files. 

Globalmapper has a "generate watershed" function that might be useful

[pyrodogg]

Hmm doesn't look like that watershed feature is available in the trial. And buying that right now is far above my budget for a whim of a hobby.

[Boyd]

Did you look at the File menu? That's where it is in the full version.
____________________________

Combine Terrain Layers...
Generate Contours...
Generate Watershed...
Rectify (Georeference) Imagery...
____________________________

[maps4gps]

If you decide on GM, I would waite (if you could) until the new version was released later this summer.  Unless he will give you a free upgrade, the usual yearly upgrade price is about 40% of the new price and there is no upgrade path if you skip a year.

[pyrodogg]

Did you look at the File menu? That's where it is in the full version.
____________________________

Combine Terrain Layers...
Generate Contours...
Generate Watershed...
Rectify (Georeference) Imagery...
____________________________

The option is there and a dialog box comes up but when I click OK I get a message saying the utility isn't available until I register.

[Seldom]

I'm a big fan of Global Mapper, but, if all you want to do is generate marine maps and you are a programmer interested in manipulating shapefiles, you can probably do what you want using freeware and a copy of cgpsmapper Personal ($40).

[pyrodogg]

Thanks for the tip!

[Seldom]

Actually, you'll probably be manipulating the DBF files that are associated with the shapefiles. You can do this with OpenOfficeCalc for free, or with a number of database programs.

[Boyd]

Filemaker Pro will give you very powerful tools for manipulating .dbf files; I wrote about it here: http://forums.gpsfiledepot.com/index.php/topic,1594.0.html

Of course, you need to have some knowledge of databases. But you can download the fully functional free trial version and you will have 30 days to do whatever you like with the program: http://www.filemakertrial.com/nskto/form/entry.aspx

Come to think of it, Globalmapper will also give you a fully functional free license key to evaluate the program for 30 days: http://globalmapper.com/product/download_complete.htm

If you would like a time-limited key to try the full functionality of Global Mapper, including exports, simply send an email to [email protected] and we will provide one for you.

So if you can get your project done in 30 days, you're all set. 

[jbensman]

My bet is it cannot be done because I would be suprised if there is elevation or bathlmetric data accurate enough to do what you want.

If you had accurate enough elevation or bath lines.  It would not be that difficult to do.  All you would have to do is convert the bath or contour line into a polygon.  Thats pretty simple with freeware such as gpsmapedit.

Unless you want to create an entire map, your best bet would be to create a transparent overlay map.  You could have a transparent polygon with a color other than blue that would show on top of the Blue to show where the water level is.  You could have imgs for various levels and select the proper one and send it to your GPS. 

I'd thing the best option would be a transparent overlay map with dept contours if you could find the data. 

[Seldom]

He's interested in Lake Powell.  If he could find contour data from before 1960, the Glenn Canyon Dam wouldn't be there.  He'd be missing all the silt build up, of course.  Glad I'm not looking for his data, but it would sure be interesting if he gets any results.

[frankm]

I've been searching for answers to the same question. Last year I damaged my jet boat due hitting rocks just under the water. This year I purchased a Garmin 526s with "Safety Shading" to help avoid those rocks only to find that the map is set for maximum lake level, and would allow me to drive my boat onto the shore before warning me of danager. I'm trying to find a way to adjust it in order to have the "Safety Shading" actually warn me of possible boat damage adjusted for current lake levels.

Did you find a solution?
Thanks,
Frank

[Talon]

Humminbird branded locators in combination with Lakemaster/Humminbird map chips give you the option of adjusting depth contours relative to water levels, thus changing the safety shading.  This feature only works for the surveyed lakes on the mapping chips though.