TopographyData
A metatype for wrapping topography data.
Attributes
| Name | Type | Description |
|---|---|---|
| path | string |
Path to the topography data or nil for a geoid. |
| offset | number |
Global offset applied to the topography data. |
Note
The data offset can be modified but not the path attribute. One can also
directly add or subtract a number offset to the
TopographyData table. Note that the result of this
operation is a shallow clone of the initial data as returned by
clone.
Constructor
The TopographyData constructor takes zero to two arguments as shown in the synospis below. If no argument is provided a flat topography with zero elevation is assumed, i.e. a geoid. If a path is provided as first argument then it must refer to a topography data format supported by the TURTLE library: ASC, GEOTIFF, GRD, HGT or PNG. Global model with multiple data tiles are also supported, e.g. SRTMGL1 or ASTER-GDEM2. In the latter case, path points to a directory containing the topography tiles. In addition, the topography data can be shifted by a global offset provided as an extra argument.
Synopsis
pumas.TopographyData((offset))
pumas.TopographyData(path, (offset))
pumas.TopographyData(data, (offset))
Arguments
| Name | Type | Description |
|---|---|---|
| data | TopographyData | Another TopographyData instance (see the clone method below). |
| path | string |
Path to a topography file or to folder containing topography tiles. |
| (offset) | number |
Global offset applied to the topography data. Defaults to 0 if a path is provided or to the initial data offset otherwise. |
See also
TopographyData.clone
Get a shallow copy of the TopographyData. The cloned object refers to the same data but with an independent offset. In order to get a deep copy of the data one should instead create a new instance with the constructor.
Synopsis
TopographyData:clone()
Arguments
None, except self.
Returns
| Type | Description |
|---|---|
| TopographyData | Shallow copy of the topography data. |
See also
TopographyData.elevation
Get the topography elevation at an Earth location. The input location can be specified by providing its latitude and longitude or by providing a point instance (e.g. GeodeticPoint, CartesianPoint), as detailed in the synopsis below.
Synopsis
TopographyData:elevation(coordinates)
TopographyData:elevation(latitude, longitude)
Arguments
| Name | Type | Description |
|---|---|---|
| coordinates | Coordinates | Point coordinates, in m. |
| latitude | number |
Latitude, in deg. |
| longitude | number |
Longitude, in deg. |
Returns
| Type | Description |
|---|---|
number or nil |
Topography elevation, in m, or nil if there are no data for the requested location. |
Note
Topography data are usually provided w.r.t. the sea level. In order to get the altitude w.r.t. the WGS84 ellipsoid (e.g. the GPS altitude) one needs to correct from the geoid undulations.