5 replies to this topic

[Wallgeye]

Hello everyone,

I am new and mostly clueless still when it comes to map making. I stumbled here while searching for a forum on mapping and hope I can get some guidance on things that may be obvious to you.

I like to fish, I have a sonar fish finder on board my boat that also has a GPS antenae. The lake I fish is under 1000 acres and has been ignored so far by companies like Lakemaster and Navionics, they offer bottom contour maps of lakes that are viewable on the screen of the sonar unit while on the water. I heard that you could make your own maps and got interested in map making that way.

My project has two parts. Part one, map the bottom of the lake, collecting depth and location data using a program called drdepth, I also have a program called 3dfield, this one does not work real time. Drdepth allows me to collect and display the map real time on the boat. I have a hand me down laptop I repaired on board that I use, it is connected to the GPS antenae with a serial cable. The screen is not very sunlight readable though.

Part two, the one that is giving me fits is actually making real map. The state of minnesota has a ton of aerial photos, USGS topo, and lake bottom contour maps that can be downloaded from various state agencies. I have looked online and found a mess of similar photos at mapping companie websites. The photo's they use alot of times seem to be the exact same ones I can download for free from the state.

What I am trying to do is generate a map of this lake, my map will overlay air photo's, with topo maps and the bottom contour maps so that I can see with a bird's eye view of where I am on the lake. One part of the lake was drained years ago and has a road bed running across the lake basin, I am really interested in getting that road location figured out. I find it with the sonar for about 5 minutes before I drift off of it and have to find it again. It is under about 20ft of water now.

I have Fugawi Global Navigator as the program I am using for this.

My big question concerns referencing the map. The dnr contour map is a scanned paper map, it shows some roads in the area around the lake, there is a bridge that crosses over the lake that is shown. The topo maps I have seen appear to have been cut outs of the larger 1:25000 topo map of the area. I have not seen the map legend before I downloaded a huge .sid file off the states servers. I am assuming I will have to cut out the part I want to use and refrence the cut out section for use in fugawi. Having the map legend will give me some of the data I was missing before, i.e., datum.


The air photo's are another thorn for me, same problem with nothing being geo-referenced that I have down loaded.

I have created a map like the one I have been babbling about but question it's accuracy. Everything I have read about refrencing a map keeps mentioning taking coordinates from 3 or more known points to reference it correctly. My red-neck way of doing this was to use google earth. I located a road intersection that was visible on all of my maps, picked a corner of that intersection and wrote down the lat/lon numbers that google earth displayed when I moved my mouse to that spot. I may have used another site that displayed lat/lon numbers while mousing over the photo. Anyway, that's how I referenced my map. My question, is how does a pro do this? Granted, I do not have acces to most of the toys you all do.

I am toying with taking my GPS out of the boat and driving to some of those intersections and taking a reading directly. I would love to get the numbers off of a monument, I have no idea where to even start looking to find information on those though.

I understand that the bottom contour map is probably not accurate to begin with. The air photo's show some shallow areas that I would like to fish, but also avoid if I am just moving through the area. The topo map showing the mine pit has that road I am looking for, that is in 20ft of water so nothing to hit with the boat if things are off. I am just hoping to get the most accuracy possible out of this. My google earth/mouse technique did not seem to be very accurate.

If anyone knows of any newbie sites for mapping they could point me at, or better yet a newbie forum it would be much appreciate. Who knows, you all might get some amusement out of watching me stumble around and would like to watch.

Sorry for the long post, glad I found this site, I'll be combing it for things I can use.

[Hans van der Maarel]

Well, first of all, welcome to Cartotalk!

Mighty big post you're starting out with, I'm starting to wonder whether that's a Minnesota thing (Derek!)

So if I read this correctly you want to make a map of the lake, with topo and aerial photos overlayed and bathymetry for the lake itself. Did you find a good bathymetry source or were you planning to generate that yourself with the sonar? (the catch being that you don't find out about shallows until you run into them and by that time, it's too late)

As for mapping sites... I think you found it...

[Wallgeye]

Well, first of all, welcome to Cartotalk!

Mighty big post you're starting out with, I'm starting to wonder whether that's a Minnesota thing (Derek!)

So if I read this correctly you want to make a map of the lake, with topo and aerial photos overlayed and bathymetry for the lake itself. Did you find a good bathymetry source or were you planning to generate that yourself with the sonar? (the catch being that you don't find out about shallows until you run into them and by that time, it's too late)

As for mapping sites... I think you found it...

Thanks for the reply, after posting my hello I did notice the "help" thread furth down. Slow loading page I guess.

Yes, I am trying to create a map combining an aerial photo, a topo map and bathymetry (lake depth?) information. I was planning on using the DNR lake maps for the depth data for now as I create one with drdepth. I can readily download the DNR maps. The DNR maps are older, they seem pretty accurate if you consider looking at the map and placing youreslf on the lake using shoreline reference points and thinking "I am about here!" Not sure how accurate they will be calibrated and in the computer. That data may go out the window anyways. If I even think I am close to shallow water I slow the boat down to a crawl so I guess anything shy of 100 feet from where I know there is shallow water I am not paying attention to what the map tells me the depth is.

The air-photo's have been giving me some fits, there seem to be tons of them. It appears that half the lake was photographed on a windy day and much of the lake surface is hard to see. I have seen, and think I have on disk a nice photo that shows the shallow areas I am interested in. I would love to get my hands on that in professional form!

The topo map, a 1:24k, I have downloaded the .drg (?) from the state's data deli. I can see it, I can zoom to the lake area I want. I cannot seem to cut the section out I want and get it in a form that fugawi will accept. It even still displays lat/lon in the viewer. This is the map that goes blurry on me when I zoom in using the sections I have found pre-cut online. That is not the entire drg, just that section I wanted.

This would be easy it seems if all I wanted to do was print it, or look at it on screen. It got messy on me when I tried to find a way to use it in Fugawi. I do have a couple questions out to them on this also, no reply yet, they're probably still laughing

I am inches away from buying global navigator, seems a bit much for what is now a single lake project though.

I should probably move this over to the advice thread I missed earlier I am thinking.



My troubles are seeing exactly the map/air photo I want online someplace and not being able to figure out how to get it on my computer and use it. I have files that work but I lost most of the resolution, I can't zoom in and still have a decent image to work with.

<sigh> I know it would take one of you folks here all of about 2 minutes to create what I am trying to learn to do. I been poking around with this for months.

[Derek Tonn]

Mighty big post you're starting out with, I'm starting to wonder whether that's a Minnesota thing (Derek!)

I resemble that remark!

Welcome aboard, Wallgeye. I'm not going to be any help in the GIS/GPS department, since most of the mapping work I do is as much "graphic design" or "art" as anything. However, I had to at least say hello to a fellow Minnesotan, as well as acknowledge Hans calling me out for being the wind-bag that I am.

[DaveB]

Welcome! Sounds like an interesting project.

It's true Derek has a reputation (well-deserved! ), it's also true that what he says is worth every word.

[Jean-Louis]

Welcome Walgeye
Derek, you are no wind-bag
I think there is a tendency to expect Minnesotans to be the Jesse Venturas of mapping