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Experiments with LIDAR

Started by Boyd, December 27, 2011, 09:15:55 PM

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Quote from: -Oz- on December 30, 2011, 11:15:52 AM
Wow, the nuvi does look really good.

I laugh at the Rockies comment; the grand canyon is a nightmare of topography.

It would be nice to make our own dem for the units but the good news is many of the newer ones include it so our maps can just lay on top.

Alas for those of us too cheap to spend the extra $100 for the DEMs.  AFAIC the Grand Canyon is more of a dream than a nightmare.


Third party support of the .jnx format would also do.


Soon I will make a test using my technique for an area with real mountains. There's about a 3GB file pre-installed on the 3790 called gmapdem.img that is just the DEM data. Pretty cool, if you connect the unit and look at that map in Basecamp, it looks like the lunar surface. Too bad they don't sell this as a separate product. My *guess* is that it's the same data as topo 100k, but also contains the rest of North America. Here's your Grand Canyon as seen with City Navigator :) Maybe I will use that as a target for my next test. The way the 3790 maps images on terrain is very impressive.


Quote from: babj615 on December 30, 2011, 12:47:35 AM
I have to ask now, are you going to send this information to Garmin and ask why the Montana performs so poorly?

If I did, it would probably go something like this:

When I make a map containing millions of pixel-sized polygons using unapproved software, why doesn't the Montana make it look pretty?

Are you serious?....



Quote from: maps4gps on December 30, 2011, 11:42:05 AM
Third party support of the .jnx format would also do.

Mike's todo list on (Preferred GM site now) has JNX export on it. 


I recall someone mentioned that last Spring.
If it can be added to GM, I was hoping someone would write a utility program to do it.


Interesting that Globalmapper would do this, seeing as there is no approved way to use such a file on a Garmin device. AFAIK, the firmware only supports Garmin's own Birdseye .jnx files.


Quote from: Boyd on January 01, 2012, 10:18:39 AM
Interesting that Globalmapper would do this, seeing as there is no approved way to use such a file on a Garmin device. AFAIK, the firmware only supports Garmin's own Birdseye .jnx files.
Could you elaborate?  I don't use Birdseye, so I don't know.  IIRC using JNX files involved a firmware hack. Is your point that GM's JNX files would be useless without a firmware hack?


Yes, exactly. It's also my understanding that, for this reason, the topic is not appropriate for discussion here.


After a lot of trial and error, I now have

* Color terrain based on the slope direction shader
* Very similar rendering between Mapsource and a variety of devices
* Map tiles based on USGS 24k quads with ~110,000 polygons

These are "blockier" than I would like, but they seem to need to be like this in order to render correctly on everything but the Nuvi 3790. IT works on the 60csx, but has pretty questionable value... it really needs a high resolution screen.

I processed the full resolution TIFF file in Photoshop where I used the Pixellate > Mosaic filter with a setting of 8, then applied a custom 32 color palette. This was imported back into Globalmapper and vectorized with a match setting of 16. Using the 32 color palette seemed to be the trick that finally made this work, by creating larger polygons due to a more limited number of colors to match.

This probably sounds harder than it really is. Now that I have a methodology, I can put together the whole map relatively quickly - it will only contain 12 tiles. Not quite what I had in mind when I started out, but not sure how much better I can get - although I'm going to continue trying.  :)


Looks good to me. Congratulations.


I have been spending WAY too much time on this, but I've learned quite a bit along the way....

* Mapsource does a really nice job of rendering the map, both in terms of color and detail, not to mention speed.

* While some of the earlier screenshotslook nice, it just doesn't look very good on the Montana's screen. I guess it's a trade-off when making a good transreflective screen - colors are very de-saturated and lack contrast. My Oregon 400t was much worse. 60csx is not too different either, but the nuvi's with their bright backlights look more like the computer screen.

* Small polygons just don't render correctly on everything but the Nuvi 3790 - they turn into blobs. Some rounding of coordinates must be happening.

Now I have managed to get a good workflow at making this kind of map - about 20 minutes to make one finished .img map tile. So I made a test map in the previous style with 6 USGS quads, and it looked great in Mapsource but terrible on my Montana. So back to the drawing boards once again...

I decided that the map needed to be more colorful to look good on the GPS and also convey information about elevation, so I turned to the Globalmapper Atlas shader. It was a long process sorting out the best way to do this, and I will skip the details and only say, "it's all about the palette". Here I was struggling to map 256 colors into 72 custom types before, but that was exactly the wrong approach.

Instead, the best results are produced with very small palettes. I settled on only 16 colors after a lot of experimentation. And the whole key to making this work is to use a setting of match distance=0 when vectorizing in Globalmapper. With a small palette, this produces more pixels that match and therefore larger polygons. The tiles I'm currently using have ~50,000 polygons each and result in .img files ~2.5MB each. They are pretty responsive on my Montana, although it's probably Garmin's fastest unit.

I am using a little trick to help keep the polygon count down. I chose a color that seems to appear a lot in these maps - and often as very small polygons. When processing in Filemaker, I flag these polygons, then delete them after re-importing the shapefile. I have my map background defined as this color in the custom .typ file, so you see through the missing polygons to the background, giving the same effect as if they were still there. This results in ~15% few polygons in my tests so far. Further study might improve this.

I also have another method, but not really using it yet. I can use Globalmapper to generate an area and perimeter attribute before exporting the shapefile. I could then use this data in filemaker to discard small polygons within a given range of colors (close to the background color). I suspect there's a lot of image processing like this that's possible, but not sure if it's needed since I've already greatly reduced polygon count.

Still tweaking this, but here are some examples comparing Mapsource to the Montana. No matter what I do, the Montana just refuses to render as much detail as Mapsource. However, in the sequence below you will notice that as you zoom in on the Montana, the detail seems to actually be there. You just need to zoom in much farther to get it to show.


Quote from: maps4gps on December 29, 2011, 07:43:09 PMWhen GM displays a DEM, it displays a combination of the elevation data and slope shading it creates from the adjacent elevation values.

Just wanted to add that you are quite correct here. Nevertheless, I like the effect of hillshading.  :) The following graphic shows the range of elevations (in feet) in the images above. This scale is valid over the full range of the map I'm making - which is basically the whole southern part of New Jersey. As I said, it's really flat around here!


This sure is an interesting thread and I am enjoying reading the posts. Maybe I will even learn something somewhere along the way.

Not sure I believe the Montana processor to be faster than a Nuvi 3790, however (but that is another thread)  ;-)

Thank you for the enlightenment!

Garmin GPSMap 60cs, Dakota 20, Colorado 400t, Oregon 300/400t/450/550t/650/650t, Montana 650, Lowrance Endura Sierra, nuvi 3790, iPhone 3G/4/4s
Geocaching ID: Atlas Cached Ambassador


Thanks. For some reason, the Nuvi 3790 balks when using a highly detailed map as soon as you zoom out past .2 miles. Have seen this with several maps I've made. Seeing the same thing here too.