Puget Sound Lidar Consortium

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Data:

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Here you can download DEM rasters, ASCII files, geo-referenced topographic images and data from other agencies.
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Other Information:

Metadata
Data Coverage and data Index
Frequently Asked Questions
Disclaimer
Topographic images
Posters and miscellaneous image files
Note about formats for raster elevation data
About PSLC lidar data
Lidar artifacts
Citation Format
Update Policy
Technical Assistance

Disclaimer: 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.

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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

Advice for building contour lines

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Posters and miscellaneous image files

(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

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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.

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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.
The SPCS zone code for Washington North (WA_N) is 5601 (The FIPSCODE is 4601)
The SPCS zone code for Washington South (WA_S) is 5626 (The FIPSCODE is 4602)

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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.

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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.

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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.

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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. If you can't find what you need here contact us.

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