Topographical Maps/Charts

[city_graphics]

I know this was discussed a long while back but it is still difficult.

Does anyone know how to get a good digital chart of like Lake Erie?

I tried NOAA but still a problem, I downloaded Wilbur and it won't open any files.

I would like a good quality digital chart not a scanned image.

Thank You

[billp]

Rodney,
I have had good luck in the past when ordering from - www.mapmart.com (http://www.mapmart.com)
Their maps may not fit the "digital map"category, but they have almost every variation of DEM maps out there

[dana_swift]

You can download free digital elevation models (DEM) files from the USGS site:

http://edcftp.cr.usgs.gov/pub/data/DEM/250/E/

These are DEM files compressed as GZ archives. Most zip programs can read GZ archives, as they are closely related internally.

USGS has the entire united states on their website for free download. Converting DEM files to something else you can use to create a cut file will require a GIS program. Look around there is free software out there (watch out for viruses!)

If working out the annoying details is alright with you, you should be able to get all this for free..

D

[denver]

Rodney, are you looking for data for lake bottoms? I've looked for that also, without much luck. Everything I've found is for dry land. I would be interested in any source for lake bottom data you happen to discover.

I've used microdem to create the grayscale images from DEM data with good results.

Thanks,

Denver

[jseiler]

There was some discussion here:

http://www.talkshopbot.com/forum/messages/312/26264.html

I think this links to the process on vectrics forum about how greg and I got this to work using cut3d and accutrans.

John

[city_graphics]

Thank You all. I will try to look into all of your suggestions.

[dana_swift]

Rodney, how much detail do you need? If you use the grayscale method the Z resolution is "ok" at best.

I have written DEM reader software in the past in the as well as DLG and other GIS primitives. Since that was all written for a former employer, I don't have the software, but I haven't forgotten how it works.

Is your project a commercial application or just a personal interest? I find the topic interesting but not enough to go code up a reader for fun. Who knows tho.. what customer lies around the corner? If I get any call for more than a DEM or two, what I would do is write a (gz)->DEM->SBP file converter. Sound like an interesting project... all three boxes have been checked at one time or another.

D

[city_graphics]

I am going to run some test sales online before I get too detailed. I was at a boat and RV show over the winter and a booth was selling topographics of the great lakes for $450.00 per lake 18"x24" and they looked like layered luan plywood cut on a jig saw. I know I can do better with the BOT.
See the attached sample. I copied a color chart from Google Images and traced it then turned it into a part file. It cut great but probably not even close to the actual contour of Lake Michigan. Have a look.
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[dana_swift]

This is a natural project for the bot.. its just a matter of getting the data and figuring out the path to a satisfactory SBP file.

Good luck!

D

[kfitz]

Maybe something here?
http://www.ngdc.noaa.gov/mgg/greatlakes/lakeerie_cdrom/html/e_gmorph.htm

Actually, Lake Erie is so shallow and unremarkable that you should just be able to do a pocket with a round-nose bit and nobody would know the difference. I think 1/16" deep over 4'x8' would be perfect ;-)

[dubliner]

With Johns help I was able to convert a DEM to a Cut3d file & preview it. I haven't cut it yet but it looks interesting & should cut like a usual 3d model but, I would like to know how to cut the a topo map with the contour lines in the typical format & not smoothed out, has anyone done that yet? Neville

[scottcox]

Neville,

I use a GIS program called Manifold, from manifold.net. I can take DEMs in and apply contours, then export those contours to DXFs and use a pocket toolpath for each. It's very labor intensive but it can be done.

[jseiler]

Here's a tutorial using microdem for simple contour maps. I've not tried this, but it looks like you can get microdem to spit out contours, save as a picture, then digitize. Then the fun begins setting up all the areas to cut at the right depth.

http://freegeographytools.com/2007/elevation-and-contour-line-display-in-microdem-make-your-own-simple-topo-maps

[dubliner]

Funny thing John, I thought that I could do it that way, but I thought while that would be possible that would be the hard way & then somebody would come along & tell me the easy way. Oh Well!

[jseiler]

If scotts way spits out dxf's, that might be the easy way. The fun would be getting all the toolpaths right, but preview in partworks/vcarve would really help you know if you were doing it right before you cut.

There's probably a better way, but I haven't tried doing contour maps, so I don't know it. I'd have to play around a lot to see what worked. If you find a good way, please share it.



My first attempt would be to get the iso lines somehow, offset them outward by about .1", pocket the rest with a 1/4" bit at each level, and trace the true edges with a 1/8" bit if the model was pretty small to get the detail of the contour edges. I certainly don't know if that's the best or easiest way, but that's what I think I'd try first.

[denver]

One method for including additional information like contour lines, longitude/latitude, etc. might be to use a grayscale image of the DEM data. Then you can include whatever additional data you wish using your favorite graphics editor. Here's a discussion of using microdem to create a grayscale image suitable for use with PhotoVcarve:
http://vectric.com/forum/viewtopic.php?t=2305

I have read that you generally get better results if you create a 3D model from the DEM data, but so far I've only used the grayscale method, so I can't compare. Here's an example of one I did that includes some additional text as well as longitude and latitude.


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