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From time to time, we use LiDAR data for modelling in ArcGIS. Previously, we would be supplied either an .xyz or .ascii of the data, but more recently, we are also being provided .las files in addition to the .xyz and ascii's.

I was reading this article which states "Having lidar in LAS format may be obvious to the initiated but not to those new to using lidar data" and "It's binary, efficient, widely supported, and the format ArcGIS works best with". I am one of those people who fall into the category of new to using .las formats.

Normally with the .xyz and ascii, I would use Global Mapper to convert them to a raster grid (for use within modelling) and it appears that I would also need to convert the .las file as well (being a point cloud). I guess the question that I am asking is:

Are there any benefits of using a .las compared to an .xyz or ascii if I still need to convert them to another raster format (GRID or .img)?

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ArcGis has a new LiDAR dataset at 10.1 which will allow you to view your LiDAR data directly and also see more information than what's in a raster... for example you can add to ArcMap and then filter down the display to just tree classes, or just first returns!

LiDAR data contains much more than just elevation, there's intensity that is stored by default (which can assist where no orthos are available) and they should be classified to ground/non-ground at the very basic; full classification is the most useful (ground, low/medium/high vegetation, buildings, water, bridges, powerlines...) for filtering depending on what you're looking for.

Should you have access to a 3d analyst licence you can convert your LAS dataset to a raster with any cell size you desire or you can view with facets...

IMO I think that it is very wise to get both a raster (use now and with existing processes) and LiDAR data (develop new processes) in a delivery.

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If you have the opportunity to get LAS or LAZ instead of TXT ... absolutely go for it. It will be trivial for you to go from LAS or LAZ to TXT (for example with the free and open source las2txt tool from LAStools). Ordering TXT instead of LAS means to loose many important attributes that you may not care about today but will in a few months or years. It also means not being able to do any quality checks (e.g. flightline alignment) on the LiDAR point cloud. And finally, reading TXT is about 10 times slower (just because of the translation from a human-readable number to binary)

Absolutely avoid TXT as a delivery format for LiDAR if you have a choice. All the software you mentioned can natively read LAS or LAZ much faster and if you really need TXT it is trivial to get without compromising the completeness and efficiency of the LiDAR.

  • Absolutely! One of the most basic checks is point density... for example, your tender says 2 pulses per square metre, but is it really? you could zoom in and count points at random but I find it much better to count first returns on a 1 metre grid to prove that the raster statistics average meets or exceeds the requirement... you need to set NoData to 0 though, otherwise areas of water might skew the results. – Michael Stimson Aug 20 '15 at 23:24
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Point cloud files are of type non-binary or binary.

Non-binary files (also known as ASCII files) are the ones with extensions '.xyz' and '.txt'. They have the advantage of being easily opened with text editors to visualize what is in there (but it is not a big advantage).

Each line of the ascii file represent a laser return record with spatial coordinates (x,y,z) and they are separated by some tabulation character. Commentaries can be included adding ';' in the beginning of the line.

;UTM coordinates, zone 7, WGS84
;x,y,z 
154517.952000 4608174.068000 21.50
153323.350000 4600983.025000 20.78
155442.850000 4601342.034000 17.13

Other columns (variables) can be included such as return type (first, intermediate, last), intensity, etc. ASCII files are read sequentially (line by line), which will consume more time for processing.

On the other hand, binary files such as '.las' have the following advantages:

  • They are more compact in size (for storage).
  • Can carry more information than the ascii format; For example: '.las' files have the header and the variable length records (VLRs) which will allow common data to the point cloud to be stored (e.g.: file signature, file version, software, extents of the surveyed area, total number of returns, projection, metadata, etc).
  • Take less time for processing and visualization, because they can be spatially indexed and therefore, can be read by parts.

As you said, independent of the point file extension, it will require processing the data to convert it into a raster format. There are software available to perform such tasks with either type of point files.

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