Wednesday, January 20, 2010

More Custom Fishing Maps

Now I'm going to talk about my favorite source for maps, unfortunately it's only for the state of Iowa. Check your state government website to see if they have a similar thing. Since this was created mainly for agriculture use I'd bet most states with a lot of agriculture will have something like this. Modern farming uses GPS and mapping more and more to keep track of things like crop rotation, fertilizer and pesticide use. The Iowa Geographic Map Server gets a lot of it's current data from USDA National Agriculture Imagery Program.

I usually set it for 1500 x 1500 pixels squares which I can later stitch together into larger maps, for instance I have complete aerial and topographic maps of Pools 15, 16 and 17 on the Mississippi as well as Coralville Reservoir and the Iowa River from the Coralville dam to the dam in Iowa City. Center the map on the area you want by clicking on it and zoom in to 20 meters and hit the Refresh Map button, click on the map to center it better and then choose 1 meter and hit the Refresh Map button again. You can adjust the map again by clicking on it to recenter it. When you get a view you like hit the 'Download map' link at the top and download the 1x1 meter GeoTIFF. This can be imported into most GPS program and is pre-calibrated.

Here is a screen shot from a portion of a 2000x1700 meter (pixel) map in OziExplorer, you may recognize it's the same area as one of the hydrographic map screenshots earlier

Now you can hit the back button and choose another map in the exact same area. The map server has several current years as well as 1930's and 1950's maps and topographic maps. Here is a screenshot from a 1930's map same size same area. Note that this was just before they finished Lock and Dam 16 and flooded the pool. The average river levels are 6-7 feet lower than today

Next is a composite map from the two maps above. This is a little trickier to make because when you make your layers and save the finished picture you lose the geodata in the TIFF header so you have to get it back in there (Or hand calibrate). A basic overview of how I make the maps is first I open The Gimp and open as Layers the two photos with the most current color map on top. Then I adjust the transparency of the top color photo to 30% and save as as TIFF. For some odd reason you can't make this TIFF work in GPS mapping programs (At least in OziExplorer or Fugawi) it does all sorts of weird things when you resize it even though it works fine in most picture viewing programs such as IrfanView. So open it in IrfanView and resave as a TIFF. Next we need to get the geodata back in the EXIF header. Next you need the libTIFF library and GeoTIFF Tools GUI from First I open one of the original photo maps and use the GeoTIFF Tools to read the header data with the 'listgeo' button. This will also place the data in the next (2nd) box. In the third box I enter the new layered TIFF I just made and it will automatically sent it to the next (4th) box with '_gl' tagged at the end of the name. Now hit the 'geotifcp_1' button and import the finished image into OziExplorer (Or other mapping program that accepts GeoTIFFs). Here is a screenshot of the same area from the new map

Here's another set of examples, this is the same area in Credit Island Slough as one of the hydrographic maps earlier

The waypoints for the rockpiles are a little bit off, this is mainly due to the way I had to mark them, I nosed my boat up to them while the GPS antenna was in the back of the boat. I tried to nose up to each one from the same direction so they'd all be off about the same

Here's the composite map

And here's another composite map, this time showing the wingdams below the water along side Credit Island

My next post will show you some depth maps I made myself as well as some 3D bottom maps made with Dr. Depth

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