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Lidar Data Products
Digital Ground Model (DGM) Elevation
Digital Ground Model (DGM) Contour Isolines
Digital Ground Model (DGM) Point
Sample Density
Digital Surface Model (DSM) Elevation
Last-Return Elevation Data
First and Last Return Intensity Data
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Title: Digital Ground Model
(DGM) Elevation
Abstract: Also known as bare-earth
digital elevation model (DEM), Virtually-Deforested (VDF) model and Mowed
Surface. It is an interpretation of the earth’s surface where 90-95% of
vegetation and man-made elevated features have been removed. No additional
filtering or interpolation is performed on variably-space mass points prior to
TIN creation and conversion to 6-foot posted ArcInfo lattice. Elevation value is
in feet. A hillshade grid is created from elevation lattice with default
ArcInfo parameters and converted to TIF and compressed image format with same 6-foot posting
dimension. The primary user data set is tiled to township-range bounding
scheme. Data also available as TINs with a 0.0 proximity tolerance and no
breakline coding, and as id,x,y,z ASCII file. A DGM is comparable to the USGS
National Elevation Database DEM, but in a dataset of much higher resolution and
accuracy.
Metadata:
Data Formats:
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Title:
Digital Ground Model (DGM) Contour Isolines
Abstract:
Lidar bare-earth lattices at a 6-foot posting interval contoured to create a
topographic surface interpretation. A five-foot contour interval is used
for elevation ranges less than 1000 feet with a 10-foot interval used from
1000 feet on up. Some township tiles labeled as _ctr005 may contain areas
that are above the 1000-ft threshold and display only 10-foot contours. Likewise,
some tiles with a 010 filename extension may contain sub-1000 foot areas with
5-foot contours.The vector
files have also been converted to DXF format at the 7500-foot tiling scheme.
Index contours are
attributed with different index schemes. Lattice smoothing and vector
generalization/splining is used to increase usability of theme for cartography
while maintaining a high-level of fidelity and accuracy. Primary user
data set is tiled to the township-range bounding scheme.
Metadata:
Data Formats:
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Title:
Digital Ground Model (DGM) Point
Sample Density polygons
Abstract:
Lidar bare-earth points distribution classified to a generalized point density
polygons and coded as low, medium or high density. Substantial interpolation and
smoothing is applied in order to create a reasonably detailed depiction relative
to file size. ArcInfo GRID PointDensity command is executed against points
extracted from the TINs, resampled and then cleaned to shapefile polygons. The
primary user data set is tiled to the township-range bounding scheme.
Metadata:
Data Formats:
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Title:
Digital Surface Model (DSM) Elevation
Abstract:
Also called top-of-vegetation or full-feature surface. Lidar x,y and z values
obtained from the first-return lidar pulse, with no segregation as to whether
surface is manmade or natural. No editing or smoothing performed on the
variably-spaced mass points prior to TIN creation and conversion to a 6-foot
posted ArcInfo lattice. Elevation value is in feet. A hillshade grid is created
from the elevation lattice with default ArcInfo parameters, and then converted
to TIF and compressed image format with same 6-foot posted dimensions. Primary user data set
is tiled to the township-range bounding scheme. Data is also available as TINs
with 0.0 proximity tolerance and as ASCII files in id, x, y, z format.
Metadata:
Data Formats:
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Title:
Last-Return Elevation Data
Abstract:
Lidar last-return variably-spaced mass point data in id,x,y,z ASCII format. Only
data from the 3di (King County) project was retiled for warehouse delivery. No
additional editing or processing of data was performed except for quality
control evaluation steps. TINs and lattices created during quality assessment
were not preserved. Only the ASCII format of the elevation data is available and
only at the lowest-tier index level, idxp7500. For consistency with the DGM, DSM
naming convention, this set is also referred to as DLM, for digital last model.
Metadata:
Data Formats:
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ASCII text files
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What does it look like?
(same format as other ASCII files)
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What area does it cover?
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Where do internal
users find it?
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What about using
the data?
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Most GIS data users
will not have a need for this format. This format is tiled only at the
7500 ft tiling level and is useful for large-scale, detailed mapping where
knowledge or resolution of subcanopy is of interest. Also useful for
reviewing the superset from which the bare-earth files were extracted.
Contains same points as DGM and DSM files where only a sole lidar return
was obtained.
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Title:
First and Last Return Intensity
Data
Abstract:
Lidar intensity data representing relative laser pulse
intensity for both first- and last- return. Data is available only for
King County (3di) portion of project area. Vendor variably-spaced points
were histogram-equalized and converted to panchromatic GeoTiff images at
1-meter resolution. Images were gridded, mosaiced to user township-range
tiles and converted back to TIF and compressed image format. Separate last-return and
first return mosaics are available in 8-bit panchromatic format. Data is
also available as x,y, intensity value ASCII files.
Metadata:
Data Formats:
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Revised September 28, 2006
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