GLARS Data Values

DSM Data Descriptions

The table below describes the properties of the GLARS DSM elevation data.

Format	Data is stored and distributed in 32 bit GeoTIFF file format with floating point elevation values.
Resolution	GLARS DSM strip and mosaic files are distributed at a ground sample distance (GSD) of 2 meters.
Coordinate System	GLARS DSM strip and mosaic files are projected in a local UTM zone (units: meters) depending on location and based on the WGS84 datum.
Vertical Reference	Vertical reference is height above the WGS84 ellipsoid.
Elevation Units	Elevation unit of measure is meters.
NULL Values (NoData)	Data may contain void pixels or regions over lakes, rivers, and other hydrographic features. Data voids may also be present where the source imagery contains cloud cover or shadowed areas. The void areas will contain null values (-9999) in lieu of the terrain elevations.
Metadata	Basic source material and production metadata is contained within the Esri shapefile and associated text files provided for each GLARS DSM strip and mosaic file.
Accuracy	Strips: 3.5 meters CE90 (Noh and Howat, 2015). Mosaic tile accuracy has not been assessed.

DSM Strips

DSM Strip Download File Types

“dem.tif” – full data, with estimated surface elevation at each pixel. 32-bit GeoTIFF. Go here for in-depth information on how these were made. Further metadata listed in table below.

“dem browse.tif” – a gray-scale hillshade representation of the surface elevation data. Example:

“matchtag.tif” – Raster indicating DSM pixels derived from a stereo match (1) or those that have been interpolated (0).

“meta.txt” – DSM Strip metadata and metadata for the particular scenes used for that segment

“trans.mat” – Matlab file for workspace used in processing

DSM Strip Naming Convention

File naming of GLARS DSM strip files incorporate several elements related to the source material used to create the data. The example below describes the naming convention:

Key: SENSOR_DATE_STEREOIMAGE1_STEREOIMAGE2_SEGMENT_RESOLUTION_FILETYPE

Example: WV02_20150615_10300100443C2D00_1030010043373000_seg1_2m_dem

SENSOR	DigitalGlobe satellite(s) that collected the stereopair image. Intrack pairs denoted by single sensor abbreviation (e.g. WV01). Crosstrack pairs denoted by a double sensor abbreviation (e.g. W1W2)
DATE	Date of earliest source stereopair image acquisition as YYYYMMDD.
STEREOIMAGE1	DigitalGlobe Catalog ID number of the first stereopair image strip.
STEREOIMAGE2	DigitalGlobe Catalog ID number of the second stereopair image strip.
SEGMENT	Segment of the DSM strip.
RESOLUTION	Ground sample distance (GSD) pixel size of the DSM in meters.
FILETYPE	Category of file included

DSM Strip Delivery Contents

GLARS DSM strips are delivered as individual files. Note that the ortho geotiff files are not available in standard GLARS DSM products.

*_dem.tif	A 32-bit floating point elevation raster. This is the primary GLARS DSM strip data file.
*_dem_browse.tif	An 8-bit, reduced resolution (10 m) hillshade representation of the strip.
*_matchtag.tif	Raster indicating DSM pixels derived from a stereo match (1) or those that have been interpolated (0).
*_meta.txt	Text file metadata document.
*_trans.mat	Matlab workspace file.

DSM Mosaic Tiles

DSM Mosaic Tiling Schemes

GLARS DSM mosaic tiles maintain a planar projection because of their high resolution. To accommodate a projected coordinate system, mosaic tiling schemes were built for every UTM zone on a 100 km x 100 km grid. For the UTM South zones, the tiling grid begins with 01_01 at x=150,000, y=3,300,000 (-60.4°S) and ends with 67_07 at x=850,000, y=10,000,000 (equator) . UTM North tile grids begin with 01_01 at x=150,000, y=0 (equator) and end with 67_07 at x=850,000, y=6,700,000 (~60.4°N). Redundant tiles are removed where tiles from adjacent mosaic schemes overlap fully.

DSM Mosaic Tile Naming Convention

File naming of DSM mosaic files corresponds to the utm zone of the mosaic and the 100 km x 100 km utm-based tiling grid. These tiles are further subdivided into 50 km x 50 km sub-tiles for distribution at 2m.

Key: MOSAIC_TILE_SUBTILE_RESOLUTION_VERSION_FILETYPE

Example: utm10n_09_40_1_2_2m_v1.0_dem

MOSAIC	Mosaic scheme denoted by utm zone
TILE	Tile index row and column
SUBTILE	Sub-tile index row and column if tiles are subdivided
RESOLUTION	Ground sample distance (GSD) pixel size of the DSM in meters
VERSION	Mosaic version
FILETYPE	Category of file included within the distributed tape archive (TAR) file

DSM Mosaic Tile Delivery Contents

index/*.shp	Esri shapefile, in WGS84 geographic coordinates, for the tile boundary. Includes metadata attributes.
*_browse.tif	10m DSM hillshade
*_dem.tif	A 32-bit floating point elevation raster. This is the primary GLARS DSM tile datafile.
*_count.tif	number of contributing DSMs
*_countmt.tif	number of contributing DSMs excluding interpolated pixels
*_mad.tif	median absolute deviation of contributing DSMs
*_maxdate.tif	latest date of contributing DSMs in days since Jan 1, 2000
*_mindate.tif	earliest date of contributing DSMs in days since Jan 1, 2000
*_meta.txt	A metadata text file describing source imagery, creation date, registration sources and statistics.