I've received discrete return LiDAR data from a data provider, which was acquired with an Optech C-300 scanner. In addition to the LAS data, the delivery includes the trajectory information in the Applanix SBET (Smoothed Best Estimate of Trajectory) binary format.

I was hoping to visualise the SBET data in QGIS - so I used PDAL SBET Reader to convert the file to ASCII as follows:

pdal translate input.sbet output.csv

The output file includes X, Y, Z coordinates, however these don't relate to my local projection (EPSG:2157):

"GpsTime" "Y" "X" "Z"
556975.005 0.933 -0.159 931.402
556975.010 0.933 -0.159 931.362
556975.015 0.933 -0.159 931.362
556975.020 0.933 -0.159 931.362
556975.025 0.933 -0.159 931.362
556975.030 0.933 -0.159 931.362
556975.035 0.933 -0.159 931.361

The min_x, min_y is (-0.1690, 0.9110) and the max_x, max_y is (-0.1650, 0.9130).

Using the SBET file, is it possible to identify which projection the X and Y coordinates relate to? And if so, can PDAL reproject these coordinates to EPSG:2157? Or is it something that needs to be corrected by the data provider?

  • From what kind of platform and instrument were these data collected? SBET is usually used to store trajectory information, e.g. from an integrated GNSS/IMU unit. – Pete Gadomski Mar 4 '17 at 15:28
  • From an Optech C-300 LiDAR scanner. – dmci Mar 5 '17 at 11:22
  • thanks for your comments and suggestions - I've attempted to update the question further with more details and specifications. – dmci Mar 10 '17 at 10:39
  • 2
    @dmci assuming the data is from Irland, can you add the extent (min/max) of the X, Y and Z coordinates in your file? The sample seems to be all at the same spot. – AndreJ Mar 13 '17 at 6:41
  • I wrote the SBET reader, and it doesn't have much real world usage. Can you open an issue in github.com/PDAL/PDAL (cc-ing @gadomski) and possibly provide a link to some sample data? That will allow me to take a look and make sure the problem is/isn't PDAL's fault :-). Thanks! – Pete Gadomski Mar 13 '17 at 13:05

The follow up discussion from this question can be found in github.com/PDAL, issue 1524.

As commented by @abellgithub (mar/17), SBET files do not carry a Coordinate Reference System (CRS) information.

The alternative suggested was to ask the data providers which CRS was used, and then, reproject the SBET file to EPSG:2157.

pdal translate -f filters.reprojection --filters.reprojection.in_srs=<some srs> --filters.reproejction.out_srs="EPSG:2157" input.sbet output.csv  

My guess would be that the data is unprojected latitude longitude (usually WGS84, EPSG:4326), stored in radians. The precision of the SBET translation is therefore a bit low to give useful coordinates.

0.933 times 180° divided by PI --> 53.457°

-0.159 times 180° divided by PI --> -9.110°


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