On the ground with the high-res LIDAR

martink

New Member
Apr 5, 2009
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Hammonton NJ
I decided to do a little exploring this afternoon using the new LIDAR maps Boyd has linked to and given us. It's the wooded peninsula on Hammonton Lake (the Smith Conservancy). I know the main trails here very well but the Hillshade of South Jersey map showed features I'd never seen. "a" appears to be an abandoned road, "b" is appears to be a cellar hole, and "c" is a meandering side trail.

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I first went searching for the abandoned road (a). Despite what should have been a fairly obvious start at a well-defined intersection of modern trails, I could find nothing. I headed through the bramble and tacked back and forth hoping I'd come across it. The woods opened up in a few spots but I never found the trace of any sort of road.

I turned my attention to the cellar hole (b). I opened Google Maps and used it to orient myself against the shoreline in the LIDAR image. I circled around and bushwacked through some gnarly thorns (I have the scratches and torn clothing to prove it) till I was in the general area. Because the LIDAR shows elevations so well I was able to orient myself to the hills. The lower areas were your typical lowland wall of cedar trees and seeing them in the middle distance helped with navigation. Finally I saw some laurel on a slight rise and there behind it was the cellar hole. Not very different from a hundred other South Jersey cellar holes but I was proud of myself for finding it!

Cellar hole from the bottom.


Knowing just where I was on the LIDAR map, I once again looked for the abandoned road and once again didn't find it. Eventually I bushwacked my way out to an established trail.

As I came back around I thought I'd look for the meandering trail (c). Surprisingly this was relatively easy to find. There was an odd collection of undergarments about twenty feet in (ewww) but past that it was full of fallen trees and thicket and I can be pretty sure I was the first human to travel that route in awhile. But I was able to mostly follow it around back to the established trail. I guessed it averaged about nine inches below the surrounding woods, which gives you an idea just how amazing this LIDAR is—a nine inch shallow gulley shows clear as day on the LIDAR.

Anyway, it was a short exploration but fun!

ps: Interestingly, the map looks a little different in Boyd's LIDAR in the Pines 2021 (BW) map. The abandoned road (b) doesn't show up at all there. It appears as if the shadows are at a different angle perhaps?
 

bobpbx

Piney
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Oct 25, 2002
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Pines; Bamber area
Cool. Could "A" actually just have been a path at one time? It looks too narrow to be a road. How come the one I circled didn't interest you?

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martink

New Member
Apr 5, 2009
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Hammonton NJ
Good question. I assumed "a" was a road since it would have been the route to "b" but it could have been more of a path. I don't know just what kind of structure "b" was.

I've passed the cellar hole you circled a hundred times (familiarity breeds indifference?). It's right on the main road, which mostly follows the ridge and is still about ten feet wide and presumably drivable. The road was also plain as day in the 1930 aerial (the arrow marks the spot where the hole is located).

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Boyd

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Interestingly, the map looks a little different in Boyd's LIDAR in the Pines 2021 (BW) map. The abandoned road (b) doesn't show up at all there. It appears as if the shadows are at a different angle perhaps?

Yes, there are different parameters for the lighting that affect how the terrain is revealed and obviously mine are different than the NJGIN map. If you play around with the controls on my LIDAR site (which doesn't cover Hammonton) you can watch the effects in realtime and the changes can be dramatic. The NJGIN site is also a bit higher resolution, but it would have resulted in another 20gb of data and about 2 million additional map tiles if I had used the full 2 foot native resolution while offering no advantage for Burlington/Camden/Gloucester counties which are 1-meter LIDAR.

Nice report! Were you using my mobile app on your phone as you wandered around there?
 
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martink

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Apr 5, 2009
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Hammonton NJ
Boyd, that is cool how trails come in and out of prominence on the LIDAR site depending on angle. Yes, I was using your mobile app on my phone, along with the NJGIN map and Google Maps to cross-reference my location. FWIW, the slightly lower resolution on your maps showed me everything I could actually see on the ground.
 
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manumuskin

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I swear with this Lidar if I went out in the woods with a shovel and a five gallon bucket I could dig a hole and fill up the bucket then dump it on the ground beside the hole,come home crank up the computer and zoom in and see the hole and the pile next to it.Thats how good this imagery is,of course i might have to hit the refresh button to bring the imagery up to date.,
 
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Boyd

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Actually, you would have to go up in an airplane with a LIDAR scanner, turn the data into a map, put it online and wait for me to download and update my map. :D

OTOH, you could just do this and get immediate results.
 
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Boyd

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Boyd, that is cool how trails come in and out of prominence on the LIDAR site depending on angle.

Yes, and making a map from the LIDAR imagery can be frustrating since, as you have seen, there is no "one size fits all" when it comes to setting the parameters. It can bring out details in one place and hide them in another, so it's really sort of a coin-toss.
 

manumuskin

Piney
Jul 20, 2003
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Yes, and making a map from the LIDAR imagery can be frustrating since, as you have seen, there is no "one size fits all" when it comes to setting the parameters. It can bring out details in one place and hide them in another, so it's really sort of a coin-toss.
This imagery will definitely keep me busy for some time.Thanks for sharing it and making the app.I fear many briar wars are coming my way
 
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martink

New Member
Apr 5, 2009
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Hammonton NJ
I swear with this Lidar if I went out in the woods with a shovel and a five gallon bucket I could dig a hole and fill up the bucket then dump it on the ground beside the hole,come home crank up the computer and zoom in and see the hole and the pile next to it.Thats how good this imagery is,of course i might have to hit the refresh button to bring the imagery up to date.,
My 8 and 9 year olds have dug holes and filled buckets in part of our backyard and they’re on the LIDAR :)
C4626C34-03A2-4E7B-A789-2C28C26E5BEC.jpeg
 

Boyd

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Also realize that this is just bare-earth LIDAR. The full dataset is a LIDAR point cloud that contains a full 3d model of everything - trees, leaves, buildings, etc. That is just too much data and requires too much processing power for me to even think about!
 

bobpbx

Piney
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Oct 25, 2002
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Pines; Bamber area
The Navy Jet sled track site. There were 5 sets of rails, and they'd fire up a jet engine and use it to fling a deadload on wheels at the arresting gear set up at the end. I worked there awhile. Think of a deadload weighing 65,000 lbs or more hitting the gear. One broke the cable one time, and they always said they never found it again. It was used to test the purchase cables, which are stretched across the deck of the carriers to snatch the plane as it landed. The link is the shipboard deadloads used to test the catapult. I worked there too.


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