I've read up on the 1 DEM data and have compared it to a few sites we have had flown with similar results. Any thoughts on 1) using this data for 2 foot contours and 2) what it means for photogrammetry companies?
tomchurch, post: 402918, member: 10174 wrote: I've read up on the 1 DEM data and have compared it to a few sites we have had flown with similar results. Any thoughts on 1) using this data for 2 foot contours and 2) what it means for photogrammetry companies?
The data that was used on a couple of my projects was too far off to be useful.
But maybe it's better now, I would survey it and see how it is.
It could be useful for planning purposes but certainly not for design.
LiDAR is great for volumetric surveys. We use it for Quarterly reporting on a Landfill site and the occasional ex-Quarry site, which they are filling with excess spoil to eventually turn into parklands. Need to know how many more years they have on those sites. It's also good for flood catchment areas as it's better at penetrating vegetation and getting a better ground model.
Photogrammetry will always be a thing (well... until we have much better satellite imagery) as 'pictures tell a thousand words'
So since posting this we compared 4 projects that we have had flown in the last 6 months to 1 meter or 2 meter DEM data depending on location. We're in the Hudson Valley and Catskills of NY. The 1 meter DEM matched the 2 foot photogrammetry contours almost perfect on the two sites where avaliable. The 2 meter DEM data matched great in most areas but you saw some loss of detail around a creek and on sharp transitions of steep slopes. It was generally within half the distance between contours.
More testing tomorrow.
Edit... Also it appears that my phone uses an old login that I have long lost the password to. Interesting.
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NESurveyor, post: 402948, member: 8416 wrote: ............. It was generally within half the distance between contours.............
That's NMAS, as I recall.
Our county does Lidar and I've compared the geo-referenced contours to my actual field shots, and they are darn good.
As a follow up since this made the Facebook page...we've compared the 1m and 2m LiDAR data to a few other projects we did in the past. In general it's damn near the same. We found some differences under pine trees, along ditches, and the detail is not there for small rock outcroppings, etc. This is mainly with the 2m data though, the 1m data is much better in these areas but still lacked a little on the outcroppings. All of this was in 30+ acre wooded sites.
Equivocator, post: 402946, member: 6885 wrote: LiDAR is great for volumetric surveys. We use it for Quarterly reporting on a Landfill site and the occasional ex-Quarry site, which they are filling with excess spoil to eventually turn into parklands. Need to know how many more years they have on those sites. It's also good for flood catchment areas as it's better at penetrating vegetation and getting a better ground model.
Photogrammetry will always be a thing (well... until we have much better satellite imagery) as 'pictures tell a thousand words'
Just wondering when you said that LiDAR is better at penetrating vegetation that LiDAR is able to shoot through canopy to get ground shots?
sireath, post: 405148, member: 9370 wrote: Just wondering when you said that LiDAR is better at penetrating vegetation that LiDAR is able to shoot through canopy to get ground shots?
Think of Lidar as a beam of light; if sun shines on it, that's where Lidar goes too...
sireath, post: 405148, member: 9370 wrote: Just wondering when you said that LiDAR is better at penetrating vegetation that LiDAR is able to shoot through canopy to get ground shots?
As Radar said, if light can reach the ground, so can LiDAR. It all depends on the scanner (density of points) and Aircraft height and thickness of Canopy.
We've found the worst to be the grass/vegetation on creek banks/swamp land. Open bush/forest is fine, no problem. Rainforest isn't quite as easy. Thick Lantana is annoying but usually enough get through to get an accurate ground model. Thick swamp reeds/grass though, causes problems.
sireath, post: 405148, member: 9370 wrote: Just wondering when you said that LiDAR is better at penetrating vegetation that LiDAR is able to shoot through canopy to get ground shots?
LiDAR "shots" return to the instrument more than once as it hits things on its way to the ground. The last return is considered bare earth and is then used (after additional processing and QC) to generate a topographic surface.
The publicly available data in my neck of the woods is most useful for planning purposes. Don't know if I'd design a road or sewer using it though...
Wow didn't know it was that advanced. Last I tested it was still like scanning where they just bounced off canopy and unable to hit the ground shots.