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Create LIDAR overlay

Started by syncro, October 14, 2019, 03:06:33 PM

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I have a garmin GPS 66st. I would like to use LIDAR data that is available to create an overlay to send to my GPS unit. I would use this similar to the birdseye view overlays. I've searched all over but cant find anything other than on open topography but the walk-through instructions are only for data sets that they have. I found other data i would like to use. thank you so much!


As with most things Garmin, the instructions are not all that clear. It almost sounds like the custom map is generated in google earth, is that correct? And what Garmin software are they referring to, is it Basecamp?


I have been working with LIDAR data for quite some time now, starting back in 2011. These techniques are not likely to be useful for you however

This map is the end result of many years playing around with similar techniques. It was not easy to make, the result is low resolution and although it works well in Basecamp and Mapsource, it's too complex to work properly on most garmin GPS units.

This (and other lidar-based maps on my site) are more like what you want to do:

I have Garmin-compatible, downloadable versions on my other site, for example:

I'm currently building a new site for exploring LIDAR in three dimensions using WebGL.... so I'm all about working with LIDAR.  :)

But (sorry) none of this really addresses your questions. The link that Red90 posted will allow you to make very small, simplistic maps, and it might be a good place to start, but is not really going to do what you want on a large scale. It is limited to making maps that are only 1024x1024 pixels. The unfortunate truth is, Garmin doesn't want you to make big maps like this, because they could compete with their own products.

What you want is called "raster imagery" - maps that are created from pictures of some sort, such as aerial imagery, scanned paper maps, etc. Here's a related thread that discusses some of the techniques and software.

Basically, you need some software that can read the LIDAR data and render it in the style you want. I use GlobalMapper, which is rather expensive. But qGIS is free and can do many of the same things. There are some other programs in the thread above that are more user-friendly (although less versatile).

After you have created the raster imagery, it will need to be converted to .kmz map tiles that are no larger than 1024x1024 pixels each. Different Garmin devices have different limits for how many of these you can use. My Montana can use a maximum of 500. There's some confusion about the 66 series since it's new. Was just discussing this with someone who heard that it can only use 100 tiles at a time, but you can have an unlimited number of maps like this. No confirmation as to whether that is true.

But regardless, it's a very limited format that's inferior to Birdseye in many ways. There's software that will allow you to create your own Birdseye imagery however, but it gets complicated. You need to have an active Birdseye subscription for this to work (which I think is already included with your device) and then you need to jump through a bunch of hoops to trick the GPS into thinking your map is "real" Birdseye.

I don't have the time to get into all the details, sorry. But will try to answer specific questions once you get started.


By LIDAR, do you mean the DEM (elevation) data provided by the USGS?
For that, I use GRASS GIS, which is free.  If you choose to use that, I'd be happy to try to help.
I'm attaching a sample of a map I made using the DEM data and a topo map.  Is the shading what you mean by LIDAR?


Boyd and MojaveMan - I appreciate you both taking the time to reply. Ive read up on most things you've published, Boyd, and its quite impressive. I dont know that my project is worth that much effort but you've created something stellar no doubt!

MojaveMan - attached is a sample of what I have achieved so far by following the instructions linked above. Its not as precise as I would like nor am I able to actually transfer it to the GPS unit. What you attached looks very similar to what I am trying to do, but I believe I am trying to add the DTM (terrain, bare earth).


Yes, I end up with something that looks just like that (I think...).  I make a shade file by loading the DEM data into GRASS GIS, and telling it to project the sun in 3 different directions.  I then merge the three different shade files to create something like the attached - a shade file for the Solatario in Texas.

That technique was borrowed from this PDF:

I download that data from the USGS National Map Viewer:

The data product that I use for GRASS GIS is the "1/3 arc-second DEM" in .img format.  If you would like to pick a specific area of interest I'd be happy to walk you through my process...


Quote from: MojaveMan on October 15, 2019, 08:56:48 AMThe data product that I use for GRASS GIS is the "1/3 arc-second DEM" in .img format.

Sorry, that is not LIDAR-based data. This is the very old DEM that (rumor has it) was originally created by painstakingly digitizing contour lines on USGS 24k topo maps. So, it's a "theoretical model" of the terrain, as opposed to LIDAR which is "imagery" that captures actual conditions on the ground. There's a huge difference here.

The USGS NED 1/9 arc-second product is derived from bare-earth LIDAR, and it represents a HUGE increase in the amound of data. For the same area, the 1/9 arc-second data will be 9x more data. I'm not familiar with the software you're using, but would assume it could handle 1/9 arc-second in .img format as well.

The 1/9 arc-second LIDAR has a nominal resolution of ~10 feet (~3 meters) per pixel, but it is now being replaced with very high resolution 1-meter LIDAR. This is the data I work with now myself. Compared to the 1/3 arc-second data you use, a map file of the same area would be about 80x larger!  8)

Anyway, it's all just DEM and the same software should work with it. The problem will be, the Garmin custom map format is so restrictive (due to the tile limit), you'll only be able to cover a tiny area with a map made from high resolution LIDAR data.

Do some quick math - we'll assume your device only supports 100 map tiles. Each tile can be no larger than 1024 x 1024 pixels (this is constant for all Garmin devices). So, let's say you make a map 10 tiles wide x 10 tiles high (total of 100 tiles). That will be a total of 10240 x 10240 pixels. And with 1-meter LIDAR, that's an area roughly 10km x 10km (a little over 6 miles x 6miles).

In the same scenario, using the lower resolution 3-meter (1/9 arc-second) LIDAR, you could cover about 19 miles x 19 miles. The only way around these limits is to create your own Birdseye imagery, which can be done with several programs (although most of them are not free). You might look at section 6 of my tutorial, although it is based on Mobile Atlas Creator. However, the information about tile limits (and getting around them) is applicable regardless of the software that you use.


According to this page:

the data set I am using is generated using either LIDAR or lsFAR.  Unless I am misunderstanding what they are saying.  Looking at my shaded topo, you can see many areas with details that are not reflected in the topo data at all - so I highly doubt the shade data was generated from the topo data.

Your math does hold, except for one thing:  I can resize the files very easily and cover much larger areas with much smaller data.  It really depends on the resolution you require...and as I have pointed out in past posts regaring Custom Maps, you don't have to put every custom map on the Garmin all at once.  When I go to Big Bend, I load up my Big Bend maps.  When I go to somewhere else, I just load those maps.  Its not like I can cover a very large area in one trip....for something like the PCT, I could easily carry multiple microSD cards.
For my purposes, I think the data I use is more then adequate.  I am able to massage the data quite a bit and what you see in those images is higher resolution than the original 1/3 arc-second.  I have tried the 1/9 arc-second for some maps, but it isn't available everywhere, so I looked at what the 1/3 arc-second was providing me, was happy with that, and made it my standard around which I make my shade.  Taking a look at the topo map I posted, I think my own shade is 100 times better than their layer of shade, and provides much more detail.  At least, I'm very happy with those results...and I am my own customer :)

But it does beg the question - what form of output are you looking for, syncro?  Will a custom map suffice?  I have to wonder if there isn't some way of turning this into a format more readily consumable by the Garmin as some sort of transparency layer....


Quote from: MojaveMan on October 15, 2019, 09:30:04 AMYour math does hold, except for one thing:  I can resize the files very easily and cover much larger areas with much smaller data.

Not sure what you're saying here.... you can take 1-meter LIDAR and resample it at 100-meters per pixel. Doesn't seem much point in doing that, the whole appeal of LIDAR is the details that it reveals on the ground. If you just want low-resolution shaded terrain, then you're wasting your time with LIDAR, just use the standard 1/3 arc-second stuff.

Didn't read that link carefully, but from what I gathered the isFAR data is only for Alaska. Did not see anything indicating the 1/3 arc-second data is LIDAR-derived. This is an old dataset, available long before LIDAR. AFAIK, they are not updating it anymore (with the exception of Alaska?)


Quote from: Boyd on October 15, 2019, 09:39:50 AM
Did not see anything indicating the 1/3 arc-second data is LIDAR-derived.

The 1/3 arc-second data is discussed in the "Seamless" section, which is part of the "Standard DEMs".  If you read the section about the Standard Dems you will see:
"Seamless DEMs are produced by blending only the highest quality project data into a continuous terrain surface for the U.S."

And what is "Project Data"?
" Project-based DEMs are available for the full areal extents of projects when produced from light detection and ranging (lidar), or as one-degree blocks with overedge when produced from IfSAR."

I'm attaching an extreme close-up of the shaded topo I posted above.  If the shade was based on the topo data, I don't think the detail that exists in the shade would be there...and when I put this image into google earth, there is, indeed, a knob there in the terrain just as the shade indicates.

By *sheer* coincidence, that shade is about 1 pixel per meter.  I pulled it up in Google Earth, and that knob is about 57 meters across - and the pixel count is about 33 across by 47 tall.


Seems like the key to that is the disclaimer "when produced". But, really, I don't know. In the past 1/3 arc-second data was certainly not LIDAR. Maybe they are upgrading it? Regardless, 1/3 arc-second is very low resolution, about 30 feet per pixel. That will only be useful for providing a general idea of terrain at low zoom levels. It will not reveal interesting surface detail when you zoom way in.

But if that suits your needs.... nothing wrong with it. :)


Anyway, back to syncro - do you think a custom map here will meet your needs?  Do you think this resolution is too poor?

As I mentioned in an edit to my last post, by sheer coincidence, its about 1 pixel per meter.  BUT, its based on 1/3 arc second, and nothing I am doing is really improving on that original resolution beyond a simple resize.


Quote from: MojaveMan on October 15, 2019, 09:44:52 AMI'm attaching an extreme close-up of the shaded topo I posted above.indicates.

FWIW, here is an example of 1-meter LIDAR at full resolution

This view would be equivalent to the resolution of 1/3 arc-second data (although it was created by down-sampling the hi-res imagery)

The 1-meter LIDAR is especially interesting in my flat, coastal area because it reveals things you won't find on topo maps or aerial imagery, such as overgrown cellar-holes of old structures. You can see some examples in the beta version of the new software I'm writing:


Can you disclose your source for your 1 meter data, and about how much of the country is covered?