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I have Lidar data which contains multiple .las files for an entire quad. I have figured out which .las is the area I am looking for. I was told the data is in 1.4 meter resolution and would work to create a contour map with 1 foot intervals. So that's what I have to work with.

I am not sure what the 1.4 meter resolution means or how it helps to create 1 foot intervals. Would the first step be to use the las2dem tool? And what would I set the step size/pixel size to?

I have created a DEM by inputting my .las file, no filter, pixel size:1. I then used raster>extraction>contours and input my DEM with interval set to 1. Is this correct for 1' intervals, or is there something I need to do to compensate for the 1.4 meter resolution of the .las?

I am mostly confused on how to make sure the intervals are set to 1 foot and not 1 meter, and what the 1.4 meter resolution means.

Also, I am working in QGIS and using the LAStools set.

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    This might be easier to answer if you can tell us what tools you are using and what processes you're following. – BradHards Mar 5 '15 at 23:47
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    There is an edit button beneath your question that you can use to revise it with more details. I recommend thinking of "about a paragraph" as being a question (or answer) of minimum length. – PolyGeo Mar 5 '15 at 23:57
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    Contour creation is quite subjective.. what's a good contour anyway? Do you want them to be pleasant, engineering... or is the issue that you've got your data in metres and you want contours in feet? What data have you got to create your DEM from? – Michael Stimson Mar 6 '15 at 0:18
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BradHards is right. If you let us know the environment you are working in the stackexchange community can narrow down the answers specific to your tools. For now I will answer the high level question of what 1.4m resolution means. Forgive me if I provide basic info you already know, but I am unaware of your level of understanding and don't want to skip anything.

A raster is a simple a grid of cells each of which has a value (in this case elevation) when your resolution is 1.4 meters it means that each cell in the grid is 1.4 x 1.4 meters. Anything inside this cell will be read as having an elevation of, lets say 10feet. Does that mean that every spot in that 1.4m cell is exactly 10ft? No it does not. So if you think of a 30m resolution DEM, that is a large area and would produce useless results when creating 1 foot contours because most the information would be extrapolated anyways. As a rule of thumb I don't usually make contours less than the resolution of my DEM (which is ~3ft in this case), but I certainly wouldn't scrutinize 1ft contours from 1.4m data for high level analysis.

Hope that helps!

  • This is not necessarily true. In lidar terms, 1.4 meter resolution may be referring to acquisition post spacing or mean point spacing after processing. – Jeffrey Evans Mar 6 '15 at 19:09
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    +1 for "As a rule of thumb I don't usually make contours less than the resolution of my DEM." I was thinking the same thing. – elrobis Mar 7 '15 at 1:45
  • There may be some confusion between horizontal and vertical resolution here. Typically the 1.4m will refer to a horizontal resolution. This has nothing to do with the vertical resolution, which for most LiDAR data is well below +/- 1ft (this can usually be found in the LiDAR acquisition report). I would have no problem making 1' contours from a 1.5-2m DEM. Contours are primarily a visualization tool that conveys the general topography of an area, and I think OP has what he needs to achieve that. If high-accuracy analyses are the goal, its better to work with the raw raster data. – JWallace Mar 10 '15 at 15:33
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With my experiences with LiDAR pointcloud data (.las) files and LAS Tools you can set your own resolution. First you will need to filter out anything that isn't ground or water to get an accurate DEM filter. From you can use the LAS Toolset to create a LAS Dataset (.lasd) and from there you can create a DEM raster by using the LAS2DEM tool. Here is where you choose your resolution, and you can make it 1 foot resolution. The rule of thumb saying "don't make contours less than the DEM resolution" is valid, and this way you are changing the resolution so you can use your desired 1 ft contours. I used ArcGIS Desktop and LAStools, however I have heard of people using the toolset by itself to create this, so you should be able to do that with LAStools and QGIS.

Here is a document that I found that gives a walkthrough for using QGIS to extract a DEM from LiDAR data using LAStools.

Here is the video that I followed to create a DEM using ArcGIS and LAStools.

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