| the Christmas Island 2003 GIS online
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| Dataset | |
| Title | Airborne Laser Scanning |
| Custodian | Geoscience Australia |
| Jurisdiction | Australia |
| Description | |
| Abstract | Airborne Laser Scanning contains ESRI
shapefiles constructed from ground height data points. The
heights were obtained from an airborne laser scanning survey conducted by AAM
Surveys Pty Ltd. The shapefiles contain surface heights in metres for the
eastern half of Christmas Island. |
| Search Word(s) | DEM Digital Elevation Model IMAGES Tiff PHOTOGRAPHY AND IMAGERY Digital Elevation Model PHOTOGRAPHY AND IMAGERY Raster PHOTOGRAPHY AND IMAGERY Grid |
| Geographic Extent Name(s) | Christmas Island Edition 2 1995 1:25000 for the Australian Nature Conservation Agency - AUSLIG Mapsheet 94/068 |
| Data Currency | |
| Beginning Date | 11SEP2000 |
| Ending Date | 16SEP2000 |
| Dataset Status | |
| Progress | Shapefiles have been made for the eastern part of the island only (this can be seen above). |
| Maintenance and Update Frequency | As Required |
| Access | |
| Stored Data Format | DIGITAL - ESRI shapefile |
| Available Format Type | DIGITAL - ESRI shapefile |
| Access Constraint | Restricted, see contact details below. |
| Data Quality | |
| Lineage | In 2000 AAM surveys conducted an airborne laser
scanner survey of the eastern portion of Christmas Island. AAM
surveys divided the eastern part of the island into 36 2km x 2km grid
squares. Geoscience Australia was provided with a set of ground
heights in metres, and the GPS location in MGA (GDA94) units of each height, for
each of the 36 grids. Geoscience Australia converted each height
dataset into a text file and imported each file into Microsoft
Access. This height dataset was then exported in dbf format, and
imported into Arcview. The databases were then added as event
themes into Arcview and converted into shapefiles corresponding to each
of the 36 2km x 2km grid squares. Previous versions of CIGIS had
produced DEM tiles based on a different grid tile system. The
36 shapefiles were adjusted to align with this previous tile
system. This was done by merging shapefiles adjacent in the
north-south direction and clipping them according to the extent of the
previously used tile. In order to minimize areas of ocean or no
data, shapefiles containing less than 30% land within the new 2km x 2km
grid were merged with adjacent shapefiles, and then clipped to remove
excess areas of ocean or no data. As a result, coastal
shapefiles, and inland tiles located at the extent of the airborne
laser scanner flight path deviate from the standard 2km x 2km grid tile
size. The end result consisted of 27 shapefiles, 17 of
which were 2km x 2km. |
| Positional Accuracy | AAM Surveys Pty Ltd Indicate that the horizontal accuracy of the airborne laser scanner
is between 0.3 and 0.5 metres (airborne laser scanner positional accuracy). The Airborne
Laser Scanning shapefiles mimic this accuracy. |
| Attribute Accuracy | AAM Surveys advise that the heights recorded
for 105 test points were within 0.23 m at the 68% confidence level. The author interprets this as meaning the accuracy of the heights will nearly always be better than half a meter (airborne laser scanner height accuracy). |
| Logical Consistency | All items within this dataset are ESRI
shapefiles that consist of a series of land surface heights. |
| Completeness | Shapefiles have been produced for the eastern half of the island only, as only the eastern half of the island has been surveyed with the laser scanner. More Airborne Laser Scanning shapefiles can be generated by GA upon request (eg using first returns) on a cost recovery basis. |
| Contact Information | |
| Contact Organisation | Geoscience Australia |
| Contact Position | - |
| Mail Address | Cnr Jerrabomberra Ave and Hindmarsh Drive |
| Locality | SYMONSTON |
| State | ACT |
| Country | Australia |
| Postcode | 2609 |
| Telephone | (02) 6249 9479 |
| Facsimile | (02) 6249 9983 |
| Electronic Mail Address | Keith.Porritt@ga.gov.au |
| Metadata Date | 9-12-2003 |
| Additional Metadata | |
| Projection | CIG85 |
| Printed | December 2003 |