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Create LIDAR overlay

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

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LOL, nothing to "disclose" there, it's available from the National Map, just like other elevation products. If available, you'll see 1-meter DEM listed in a search.

FInding coverage areas is frustrating on their site. They often show big polygons of available data, but when you look at the downloads, only a little corner of that area is actually covered.

But I think there are large parts of the US (maybe even the majority of it?) with no high res LIDAR data available at all (neither 1/9 arc-second nor 1-meter). Fortunately, there is very good coverage of my small state of NJ, and it's more than enough to keep me busy making maps. :)


Just catching up and a lot of great discussion, thank you. I dont think I cant respond to all of it but I certainly read all of it and appreciate the input.

I am interested in a custom map with fairly high resolution (able to detect features around 1-3 meters in size). The size of the map would cover maybe a square mile (or a few smaller ones) and the most important feature is the ability to view the map on my handheld GPS. Currently, I use LiDAR to pick points of interest and grab the GPS location of that feature and log it into excel. I then load that spreadsheet into a google map then save that file as a KML that then gets transferred to my device. When I am in the field, I am able to locate the POI just fine, but then have hard copy print outs of the LiDAR for reference...its not all that great bouncing between GPS topo lines and hardcopy LiDAR print outs.

As a response to the first reply in the thread, I was able to play around with google earth pro enough to do a decent overlay. It took a few trys but I was able to line up almost all features with my pins, however, I cannot transfer the overlay to my device.


Why were you not able to transfer it? Connect the GPS to your computer and open the Garmin folder. If necessary, create a folder named CustomMaps. Copy the Google Earth .kmz file to that folder.

You must use .jpg images for the .kmz, it will not work with .png images. Make sure that the image you created is no larger than 1024 x 1024 pixels. Also, only use letters and numbers in the filename. There's an old bug where a file named my_map.kmz would not work but mymap.kmz does work. This may have been fixed though, not sure.

I assume you already know where to find the LIDAR imagery, since you're already using it? If it has 1-meter resolution, then each map tile can be about 1km x 1km (1024m x 1024m). You can use 100 of these tiles at the same time.

For more versatility, you would download the actual DEM files from the USGS, then use some software to render them in whatever style you like. Sounds like MojaveMan has some ideas for this. I use GlobalMapper, which makes all of this trivial, and it can directly create the Garmin custom maps. It is expensive software however.

Again, look at the other thread i linked to:

As discussed there, qGIS and mapc2mapc are useful tools for this. qGIS is free, open source software Mapc2mapc is not free however. g-raster is also mentioned in that thread, and is another tool that is worth a look. Again, it is not free.


I would be happy to walk you through my process, if you would like.

You will need:

GRASS GIS: free open source fully capable GIS

Imagemagick - open source image manipulation software

A DEM from the USGS.

If you would like me to walk you through my process, let me know and I'd be happy to go step by step with you either in these forums or via email.  Or, if you would like, just gimme some idea of the geographic area and I will give it a go to show you what an end-product can look like.

If you need help getting your .kml file into your Garmin, I'm happy to help with that, too.
First, did you use a .jpg for the image?
Second, how big is it in terms of pixels?  If its larger than 1024x1024 pixels, you have to cut it up into smaller pieces - a process called "tiling" it (cutting it up into square tiles).


In case you don't already know, here's how to find 1-meter LIDAR. Go to the National Map download page

Drag/zoom the map to the location that interests you
Choose "Elevation Products" (NOT elevation source)
Check the box next to 1-meter DEM
Click Find Products
If any 1-meter LIDAR is available for the area you're viewing, it will be listed


Not sure what happened, but when i was trying to transfer the map is just wouldnt take. i tried dumping it into the custom map folder, it was the right size, all that stuff. just turned on my GPS unit and its there even though it wouldnt acknowledge the transfer before.

I think for now, i have a method that works for me but may need to take up the offer to see your method, MojaveMan. Thanks again everyone!


So, I did a little bit of math to see how much area my maps are covering, and how many tiles they take.

A USGS topo map for the Big Bend area covers about 60 square miles, and takes 4981x5682 pixels (I converted the PDF to a .png at 250 dpi with imagemagick to get these pixel counts).  That will be 5x6 tiles of 996x947 pixels each, right?  Thats a total of 30 "tiles" of the 500 my Oregon 600 can use.  I could fit 16 such maps on my Oregon (really a bit more), for a total of 960 square miles, or an area almost 31x31 miles.  That isn't bad.
For the units that allow 100 tiles, that could still take 192 square miles, or an area about 14x14 miles.  Still not too shabby, and plenty big for a camping trip.
Note this is NOT the resolution I used for the map I posted above where my measurements indicated about 1 pixel per meter.  That is a map at 600 dpi.  If I were to use a map at that resolution, they would take about 6 times as much space ("only" about 200 square miles in those 500 tiles the Oregon allows me).  But the 250 dpi is really quite adequate for the Garmin's display...the USGS Topo maps are clear at that resolution, and the shade images I generate show nice details not present in the topo map all comes together quite nicely.
Given I tend to only concentrate my trips in much smaller areas, I can load up several topo maps for many different locations before ever having to worry about running out of space.


Quote from: MojaveMan on October 18, 2019, 12:03:32 PMNote this is NOT the resolution I used for the map I posted above where my measurements indicated about 1 pixel per meter.

FWIW, resolution is usually expressed as [units] per pixel - such as "meters per pixel" and not "pixels per meter".  :)