In what formats is the PSLC LiDAR data
available?
ArcInfo Interchange Files
(.e00)
ArcInfo interchange files have an .e00 extension and are
commonly know as .e00 files.
The
.e00 file format is verbose ASCII, expanding gridded DEMs to
approximately 4 times their binary size, but is easily
imported into an ESRI Grid for use in Arc-Info, ArcView and
ArcGIS.
It also carries
projection information.
These are
available online for the
bare earth and also the top surface.
File Geodatabase for ArcGIS
versions 9.2 and beyond
These are available for almost all the PSLC
projects. They have a 6-ft resolution and have both
the elevation models for the bare earth and the top
surface. You can access them via the individual
project page.
You may also find some File Geodatabases for other non-PSLC
projects
here.
GeoTIFF
Hillshade TIFF images with
world files (.tif and .tfw).
These
are simple image files that show the shaded relief derived
from DEMs by considering the illumination angle of the sun
and shadows. These files do not have elevation
information.
These are
available online for the
bare earth and also the top surface.
ASCII
PSLC Lidar data is also available in ASCII format.
We have the bare earth ASCII and
the all-returns ASCII.
The
bare earth ASCII files are composed of the
returns classified as ground.
These
files are simple text files where each line (row) has values
for easting, northing and elevation.
Each
quarter quad is broken down into 1/25
th tiles
The
all-returns ASCII
files have all recorded returns during each survey mission.
These have returns for buildings,
vegetation, etc.
They are
simple text files where each line (row) has values for
easting, northing and elevation, but they also have other
attributes such as the return number, a time stamp, scan
angle, some have intensity and classification code.
The attributes vary a little
between projects done in different years.
Reference
the metadata for the header information.
These
files also tend to be very large in size.
Each quarter quad is broken
down into 1/25
th tiles
to make them more user friendly. (There is an
execption for a couple of datasets, see
tile scheme)
Both of these datasets are
available online.
LAS
Projects from 2006 and beyond also have .LAS
files. LAS format is an open format that allows most
software packages to utilize the data. This files
contain a record for each return. Read the
deliverables part of the project report for the LAS version
being used. If a project has LAS files, you may find
them in the
project
page.
The LAS files available through the PSLC have been
compressed using LASzip software. LASzip is an open source
lossless compression for lidar point cloud data in the LAS
format that provides significant file size reductions,
helpful when downloading or storing large datasets. To
uncompress the .laz files you can use the laszip.exe tool
available in the data directory or you can download the
latest version from
LAStools.
See the laszip_README.txt in the directory to learn how to
use the tool in the command line. Alternitably, in
Windows Explorer you can also 'drag and drop' indiviual or
muliple .laz files onto laszip.exe. This will
automatically uncompress the files into the current
directory.
If you have
ArcGIS 9.x or
the most recent version with the ArcInfo License, then
you can use the “Import From Interchange File” tool in the
toolbox.
This tool is located
in a different location for each version of ArcGIS.
The easiest way to find it is to
do a search in ArcToolbox.
Once
you have it open, make sure you specify “Grid” for feature
type. You can also use the Import command in ArcInfo
Workstation.
If you have ArcGIS
9.x
or the most recent version with the ArcView
license, you can import the .e00 file by
using the “Import from Interchange file” tool under
Conversion tools in ArcCatalog. This
tool
does have a glitch. It
creates a .aux file that does not allow ArcMap or
ArcCatalog to recognize the files and you get an “Invalid
raster dataset” error message. You
will need to delete the .aux file by following the
directions in the related ESRI
Technical
Article (Article ID number 21443 in
support.esri.com
). Alternatively you can
download Import71 to import your files.
You can download it free of charge from geocomm.com.
(
http://software.geocomm.com/translators/arcview/)
This should not give you any
problems.
In
AutoCAD you will need to use the bare earth ASCII
files.
AutoCAD does not have a
translator for raster .e00 files.
For all other software check your user's manual for formats
supported. If it's not supported, you may be able to
find a translator for your software. Your software's
technical support may also be helpful.
Is
there metadata?
Yes, most of the PSLC
data has metadata. See the
project page to
find corresponding metadata. Projects from 2005 and
beyond also have project reports available. These have
further information that the metadata my not include.
PSLC
LiDAR
data is broken down into USGS quarter quads. ASCII
data is further broken down into 25 tiles per quarter
quad. Each quarter quad is subdivided into a 5 x 5
array of tiles organized from upper-left to lower-right as
follows:
01 02 03 04 05
06 07 08 09 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
The two-digit tile number is appended to the end of the file
name.
There are two exceptions. One where the tile scheme is
1/64th of a quad. The projects affected are the Lewis
County project in 2006 and the Eastern WA\OR River corridors
flown in 2007. The other exception is the Sumpter
Oregon project. This project has it's own unique
tiling scheme.
See the individual
project
page for a shapefile of the tiling scheme and also the
project report (for project flown in 2006 and beyond) for
detail on the tiling scheme.
What is the header for the ASCII data?
For projects flown from from 2000 to 2005:
For the bare earth ASCII
data it will always be X, Y, Z (Easting, Northing and
elevation).
The header information for the All-returns ASCII data
varies depending on the project year.
For projects from 2005 to the present, reference
the Deliverables section in the project report.
Project from 2000 to 2004 do not have project reports,
therefore reference the Entity_and_attribute_Information
in the corresponding All-returns ASCII metadata. You
may access these documents via the individual
project page.
Projects from 2006 and beyond
The ASCII files for these
projects come with headers included in each file.
You may also take a look a the project reports provided in
the
project page.
The best source for projection
information for project between 2000 and 2004 is the
metadata. Grid data for projects from 2005 and beyond
have metadata or projection files attached. These also
have project reports available. Both of these
documents can be accessed via the individual
project page.
In general all PSLC LiDAR data
is collected during the winter/leaf-off season from December
to Early April.
For projects flown between 2000 and 2004 reference the
metadata for a range of dates. For exact days you may
use the flight line trajectory files when available.
Otherwise, you may need to access the All-returns ASCII
data. When using the all-returns ASCII data you will
need to look at the time stamp on each return. These
documents and data can be accessed via the individual
project page.
For projects flown to 2005 to the present, you may reference
the
Project Reports for a range of dates. For exact
days you should use the
flight line trajectory files. If you choose to,
you can also use the all-returns ASCII data or LAS
files. These documents and data can be accessed via
the individual
project
page.
The return-number enumerating
system varies by project. For all PSLC Lidar data, the
scan can record up to 4 returns per pulse.
For project flown in 2000, 2001, 2002 and 2004, there is
only one field called "return#". This is the return
number for the pulse that emitted that return.
For Project flown in 2003 and 2005 (expecpt for the 2005
Olympic Peninsula project) the following system applies:
"Total # of Returns in
Pulse" (also known as "total_return#) is the total returns
that a pulse emitted (up to a maximum of 4). "Current
Pulse Return number" (also known as "return#") is assigned
as a number from 1 to 7 in a scheme that identifies which
return is the last return recorded for a pulse. See
below for a description of this scheme.
1 first return with subsequent returns detected
2 second return with subsequent returns detected
3 third return with subsequent returns detected
4 fourth return
5 first return with no subsequent returns detected
6 second return with no subsequent returns detected
7 third return with no subsequent returns detected
The 2005 Olympic Peninsula project has limited
attributes. See the
field
info
sheet.
Project flown from 2006 to the present have "returnnum" and
"numreturns". Returnnum is is the return number
emitted from a particular pulse. Numreturns is the
total number of returns emitted by a pulse.
Take a
look at the
project
page for PSLC data. Also look in the
data from other
agencies for data not acquired through the PSLC, but
provided for public distribution on the PSLC website.
How can I get ASCII data?
The bare earth ASCII data and
the All-returns ASCII data are
available
online. You will need to go to individual
project pages to access the corresponding files
Large quantities of data are also available via special
request, but it does take more time and the requester will
need to provide an external hard drive as well as postage to
return the drive. Include a list of USGS quarter quad
numbers with the request.
Use
the index shapefiles for the project to see which quads you
need. These shapefiles are available for individual
projects in the corresponding
project page.
You can submit a request to Andrew Norton at
anorton@psrc.org or at
(206) 464-7527.
I forgot my password, how do I get
it emailed to me again?
I have my password but I can’t
get into the download site.
See the
LiDAR
Access
page for a step-by-step guide to the download site.
Also keep in mind that the login and the password are case
sensitive. Make sure you enter your login (which is
your email address) correctly.
Another common problem is misspelling your
email address when you initially registered.
If you continue to have problems email Andrew Norton at
anorton@psrc.org or
Harvey Greenberg at
hgreen@u.washington.edu.
We have taken considerable
care to ensure that these topographic survey data and
derived images are as accurate as possible. We believe
most of these data are adequate for determination of flood
hazards, for geologic mapping, for hydrologic modelling,
for determination of slope angles, for modelling of
radio-wave transmission, and similar uses with a level of
detail appropriate to a horizontal scale of 1:12,000 (1
inch = 1,000 feet) or smaller and vertical accuracy on the
order of a foot. Locally, the data are of considerably
poorer quality.
Users should
carefully determine the place-to-place accuracy and
fitness of these data for their particular purposes. For
many purposes a site- and use-specific field survey will
be necessary.
Topographic images
PSLC
surveys,
web-viewable
topographic images: clickable index map
or
list
of files
Shaded-relief images in quarter-township (3 mile by 3
mile) tiles. Each image is about 1 MB in size. Includes
Kitsap Peninsula, Bainbridge Island, Seattle (with
extensions to north and south) and central part of King
County.
USGS Snoqualmie Valley survey,
web-viewable topographic images: list
of files
About
the
Snoqualmie
Valley survey
(Bainbridge Island, city of
Seattle, fused upland/marine lidar for SE Whidbey Island,
etc.)
Code and example
data for researchers
Example
all-return
PSLC
lidar data 36 MB zip file
ASCII file, one row per reflection, each row listing:
easting, northing, orthometric
height, geoid height, GPS second, return number, scan
angle, off-nadir angle, GPS week
Returns are from an area of approximately 1 x 1.4 km.
Code
for
VDF
post-processing with example data 64
MB zip file
Code
for
swath-to-swath
consistency images 60 kB tar file:
ArcInfo AML, Pascal source code
Code
for
simple
canopy characterization 23 kB tar file: ArcInfo AML, Unix system
calls, Pascal source code
Note about formats for
raster elevation data
DEMs are zipped .e00 files.
The .e00 file format is verbose ASCII, expanding gridded
DEMs to approximately 4 times their binary size, but is
easily imported into Arc-Info and carries projection
information. If this format doesn't work for you,
please let us know!
Geocomm.com has several translator
for .e00 files. Take a look at e00-to-shp and
Import71.
About PSLC lidar data
Lidar topographic survey data go through
several stages on the way to a finished digital elevation
model (DEM). The initial survey generates
- time-stamped laser range-finder distances and scan
angles
- time-stamped differential GPS (Geographic
Positioning System) aircraft position data
- time-stamped Inertial Measurement Unit (IMU)
aircraft orientation data
- calibration parameters for range measurements,
instrument position in the aircraft, and instrument
orientation in the aircraft
These data streams are interpolated
and summed to produce
- All-return point data, with values for X,
Y, Z, (time, reflection number, scan angle, ...). In
forested areas a large fraction of these reflections
are not from the ground.
First reflections from each laser shot
are easily isolated. From the first reflections one can
construct a
- First return DEM
that images forest canopy, buildings, vehicles, and
bare earth in open areas. This surface may be
constructed as a TIN (triangulated irregular network)
from the first-return points, and is most easily
visualized and transferred as a regular array of
heights (known variously as a lattice, grid, or
DEM--though TINs, digital contours, and other data
formats can also be DEMs).
To produce bare-earth topography,
reflections from trees, structures, and vehicles must
identified and discarded. The remaining
- Bare-earth point data are X,Y, Z triplets.
In forested western Washington we find that for only
circa 1/3 of all pulses have we recorded returns from
the ground.
From the bare-earth points we
construct a
- Bare-earth DEM that is the best estimate of
the topography. Again, we construct this surface as a
TIN and then sample the TIN at regular intervals to
produce a gridded DEM.
Most participants in the PSLC are
local government agencies that maintain geographic data in
State Plane projection, horizontal datum NAD83, 1991
adjustment (also known as the HPGN or HARN datum), with
coordinates in feet, thus we receive and archive all data
in this projection. The vertical datum for these data is
NAVD88.
Lidar artifacts
Crystal forest or pyrite forest
Where there are few survey points
(i.e. bare-earth surfaces in heavy timber, where there are
few ground reflections), TINning the points produces large
triangular facets where the surface has significant
curvature. Similar, though finer, textures are evident
where vegetation reflections are incompletely
filtered. Elevations are likely to be less accurate
in these areas.
Open water areas are mostly
garbage
Lidar surveying produces few survey
points on water. Mirror-like surfaces fail to scatter the
laser beam and unless the beam is perpendicular to the
surface, no light is reflected back to the detector. Or
intense reflections may lead to negative blunders, points
that are too low. Interpolation between the nearest
on-land points and sparse water points produces large
triangular facets that may not accurately reflect the
water-surface elevation. Where the water surface is
surveyed adequately, adjacent swaths may be flown at
different tide stages, producing swath-parallel cliffs.
Ideally, lidar topography would be clipped to eliminate
all open-water areas, but at present this is very
labor-intensive.
Bomb craters
Most lidar data sets contain scattered
too-low points, or negative blunders, perhaps produced
when a specular reflection or too-close ground saturates
the detector and produces an internal echo. If vegetation
reflections are removed by a
find-the-lowest-point-in-the-vicinity algorithm, true
ground points adjacent to the negative blunders may be
misidentified as vegetation reflections and removed. The
result can be a conical crater that is entirely an
artifact.
Arcs of small pits
The Bainbridge Island lidar survey
contains a few circular arcs of small pits. Each appears
to be a negative blunder for which adjacent ground points
have not been removed. The origin of these artifacts is
not evident.
PSLC Recommended Citation
Format
Format for downloaded
data:
Format:
Database Name [type of medium]. (Year). Producer
location, province/state: Producer name. Available:
Supplier, location, state, address/path/file [Access
date].
Example:
LiDAR Bare Earth DEM [computer file].
(2000-2004). The woodlands, TX:
Terrapoint. Available: Puget Sound LiDAR
Consortium, Seattle, WA
http://pugetsoundlidar.ess.washington.edu/index.htm
[April 27th, 2004].
Format for data from a CD-ROM:
Format:
Database Name [type of medium]. (Year). Producer
location, province/state: Producer name. Available:
Supplier, location, state,/Database identifier or number
[Access date].
Example:
LiDAR Bare Earth DEM [CD-ROM]. (2000-2004).
The woodlands, TX: Terrapoint.
Available: Puget Sound LiDAR Consortium, Seattle,
WA [April 27th, 2004].
Note: In this case there would be no "Database
identifier or number" since you probably just got a CD
from us.
A good reference link for citing
geospatial data resources is this site
at the University of Waterloo Map and Design Library.
Update Policy
Data is posted for download
as it is approved by the consortium. Areas within
many of the bare-earth DEMs can be improved by further
processing of the all-return point data to better isolate
bare-earth points. As we make these improvements we will
upgrade the bare-earth DEMs and derivative images posted
here.
Technical
Assistance
If you have difficulty
loading the data files into your software, cannot easily
transfer large files via the Internet, or would like
advice on the uses and limitations of these data, please
refer our FAQ's above. If you can't find what you
need here contact
us.