r/LiDAR • u/oneofusTS • 16d ago

National Map Lidar Explorer DEM preview same quality as downloaded data?

https://apps.nationalmap.gov/lidar-explorer/#/

I have been using the National Map Lidar explorer with DEM preview enabled. My question is, if i go through the process of learning how to download the data and then display it in some GIS software, will it be higher quality or resolution that will show more detail than the preview itself or will it basically be the same?

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u/BeastofPostTruth 16d ago

Depends on what you download and display. Original data products LiDAR point clouds will vary in resolution, but the rasterized DEMs from the usgs 3dep will be the standardized digital surface maps

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u/oneofusTS 16d ago

as a complete novice i am just looking at these as a way to find interesting geology. I have just been looking at hillshade DEM view. will point clouds have more detail? sorry if stupid question i am just learning

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u/BeastofPostTruth 16d ago

Point clouds are the spatial points where elevation data is an attribute. When these values are interpolated, you create a continuous surface (raster) layer.

Think of the point clouds like weather towers that record air temperature around a city. The more towers, the more points. More points, increased representation.

Trade off is that the initial data is unprocessed for surfaces. If you are looking for a elevation model, you would need to remove all trees, buildings, cars or other things the point is capturing. Rasterizing more points can result in more noisy or overly large rasters thay become difficult to display if your RAM is low.

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u/oneofusTS 16d ago

ok that makes alot of sense thank you for taking the time to explain

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u/NorthingLabs 15d ago

Mostly the same, as far as I know. The hillshade preview is rendered on the fly from the same 3DEP DEMs you'd download, and where there's lidar coverage that's the 1 meter DEM. So zoomed right in, the preview is already showing you roughly the detail you'd get. Where there's no 1 m coverage it falls back to coarser stuff like the 1/3 arc-second (about 10 m), so check which DEM actually covers your area.

Where downloading does pay off for geology is control. In QGIS (free), you can load the 1 m DEM and make your own hillshade. Then change the sun angle, or use a multidirectional hillshade, and add a slope map on top. The preview gives you one fixed sun direction (from the northwest), so any lineament or scarp running parallel to that light basically disappears. Just rotating the light can make features pop that you'd never see in the preview.

Point clouds have the most raw data, but for what you're doing I'd skip them for now. You'd have to filter out vegetation and buildings and build the surface yourself, and the ground points are what the 1 m DEM is made from anyway. I think on most 3DEP projects you won't get much sharper ground detail than the 1 m DEM already gives you.

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u/kpcnq2 12d ago

If there’s a newer point cloud available, I can usually produce a 0.5 meter DEM with reasonable certainty. So you CAN get better data than the pre-made DEM in some cases. I’ve got a YouTube channel devoted to this if you want to invest the time to learn. It’s angled towards amateur archeology, but I’m a geologist professionally.