Elevation1 DTM Technical Information

Elevation1 products
  1-m posting DTM Orthomosaic (8 bits)
Method DTM generated by automatic filtering of DSM  produced from Pleiades stereo imagery, complex areas are completed by manual stereo editing.
This product requires a minimum of  5 suitable GCP’s to be provide by the customer.
A seamless mosaic will be generated, with global radiometric  optimization & semi automatic cut lines, as long as no significant seasonal variation is present between the imagery .
Processing
  • Manual stereo editing of complex areas including areas with a high density of above ground features.
  • Detection of water bodies (sea, lake, large river) and DTM flattening.
  • Hydro Enforcement – To insure hydrologically correct drainage network, this will be limited to the major drainage network, where continuous stretches of water are visible on the imagery.
  • Image finalisation
Source data Pleiades Stereo  pair(s),
Level Primary Regular, Format DIMAP JPEG2000
Cloud coverage < 5% (Where cloud appears in the source images ,it will not be possible to calculate terrain elevation values)
Grid spacing 1m 50cm
Accuracy Absolute XY*
  • With GCPs: 1.5m CE90.
  • With Ref3D GCPs: 6 to 10m CE90**.
  • Without GCPs: 8.5m to 10.5m CE90.
  • 1m CE90
Absolute Z*
  • With GCPs: 1.5m LE90.
  • With Ref3D GCPs: 6 to 10m LE90**.
  • Without GCPs: up to 10m LE90**.
NA
Relative
  • With GCPs : 1.5m LE90
  • With : Ref3D GCPs 4m LE90 (A global slopes of up to 0.02% may be present across the dataset)
  • Without GCPs: up to 4m LE90 (A global slopes of up to 0.02% may be present across the dataset)

NA

Deliverables
(on top of the DTM & ortho)
  • Stereo model
  • Contours – 3m interval
Format
  • DTM – ASCII Grid / GeoTIFF(32bit float)
  • Ortho Image - GeoTIFF (3 bands 8bit)
Projection Geo WGS84 or UTM / WGS84 (custom projection on request).
Vertical Unit Metres
Vertical reference Elevations above mean sea level (ref. = EGM96).
Accuracy level The accuracy specification of Elevation1 is similar to the HRE10 NGA classification.
(“HRE” means High Resolution Elevation)
GCPs

It is recommended that GCP’s should be used for the creation of GeoTerrain1, customers need to provide a minimum of 5 GCP’s evenly distributed across the scene. GCP’s should be accurate to ~10cm XYZ & be visible in the stereopair.

AOI
  • Large AOIs can be covered by adjacent stereopairs; the DTM mosaic will be seamless with no edge effect.
  • Minimum area = 100 sq.km.with a minimum width of 10km.
NoData value
  • The value –32767 is set for areas where the elevation is not determined.
Metadata No additional metadata is provided with the DTM.
B/H ratio
  • The optimal B/H ratio is in the range of [0.3 – 0.6].
  • A high ratio (i.e. 0.6) is suitable for flat areas.
  • A low ratio (i.e. 0.3) is suitable for steep terrain.
Remark GeoTerrain1 DTM will only be available in areas where a high percentage of the ground is visible on the imagery. While areas that are obscured by above ground features, such as buildings & trees, where the DTM will be interpolated from surrounding areas of visible ground may therefore not produce such a high quality DTM. Areas of clouds (and their shadows) will be masked to NoData in the DTM as ground elevations cannot be computed. 

 

Elevation1 DTM Technical Information