xarray .pdt accessor#

class pdemtools.DemAccessor(xarray_obj)#

This class provides rioaxarray-compatible DataArray objects with access to custom functions and methods.

Functions are accessible via the pdt accessor: for instance, if you have a DEM loaded as the variable dem, you are able to access the terrain function via dem.pdt.terrain().

coregister(reference: DataArray, stable_mask: DataArray | None = None, return_stats: bool | None = False, max_horiz_offset: float = 50, rmse_step_thresh: float = -0.001, max_iterations: int = 5) → DataArray#

Coregisters the scene against a reference DEM based on the Nuth and Kääb (2011) method, as implemented by the PGC.

Original code available here: PolarGeospatialCenter/setsm_postprocessing_python

Parameters:

reference – reference DEM DataArray of same extent and resolution.
stable_mask – Mask dataarray where 1 = stable region to be used for coregistration. If none, coregisters based on the entire scene.
return_stats – If true, returns the transformation parameter, the translation error, and the RMS error alongside the coregistered DEM dataarray, defaults to False
max_horiz_offset – maximum horizontal offset, beyond which XY coregistration is ignored and only Z values are corrected. Defaults to 15.
rmse_step_thresh – break coregistration loop if rmse step is above threshold, defaults to -0.001.
max_iterations – max iterations to attempt, defaults to 5.

Returns:

coregistered (rio)xarray dataarray

Return type:

DataArray

geoid_correct(geoid: DataArray) → DataArray#

Geoid correct the DEM, given a geoid as an xarray DataArray. The function will attempt to reproject the geoid to match if it does not already to do.

Parameters:: geoid – A suitable geoid, as a (rio)xarray dataarray
Returns:: geoid-corrected (rio)xarray dataarray
Return type:: DataArray

get_sea_level(candidate_height_thresh_m: float | None = 10, candidate_area_thresh_km2: float | None = 1) → float#

Returns estimated sea level following method of Shiggins _et al._ (2023). If no candidate sea level is identified, None is returned. DEM must be geoid-corrected.

Parameters:

candidate_height_thresh_m (float) – Maximum value relative to geoid to be considered as SL, in m, defaults to 10
candidate_area_thresh_km2 (float) – Minimum area beneath candidate_height_thresh_m to be considered for sea level assessment, in km^2, defaults to 1

Returns:

Estimated sea level

Return type:

float

mask_icebergs(area_thresh_m2: float | int | None = 1000000.0, retain_icebergs: bool | None = False, return_mask: bool | None = False, connectivity: Literal[4, 8] = 4) → DataArray#

After masking the ocean using the mask_ocean() function, icebergs will remain. This function gives you the opportunity to mask them as well by identifying the size of connected groups of pixels and masking above/below a threshold.

By default, this function masks icebergs and retains terrestrial ice/land. However, by setting retain_icebergs = True, the function will instead mask ice/land and retain icebergs, allowing iceberg area and volume to be assessed. For accurate volume assessment, the DEM 0 m value must be set to the estimated sea level height from the get_sea_level() function. This can be automated by setting return_sealevel_as_zero = True in the mask_ocean() function.

Parameters:

area_thresh_m2 (float | int) – Size threshold between icebergs and terrestrial ice/land, in m2. Defaults to 1e6 m2 (1 km2)
retain_icerbergs – By default, this function masks icebergs and retains terrestrial ice/land (by masking pixel groups below the threshold area). By switching the parameter to True, the function will instead mask out larger pixel groups and retain the smaller icebergs.
return_mask (bool) – If True, returns mask of icebergs (where icebergs = 1). If False, returns input DEM with icebergs masked. Defaults to False.
connectivity (int) – Connectivity with which to calculate iceberg regions. Must be 4 or 8. Defaults to 4.

Returns:

Either masked DEM or mask as xarray DataArray, depending on the input value of return_mask.

Return type:

DataArray

Returns a DEM with mélange/ocean regions filtered out, adapting the method of Shiggins _et al._ (2023). If no likely sea level is identified, returns the original DEM.

WARNING: The DEM must be geoid-corrected for this function to work correctly.

Parameters:

candidate_height_thresh_m (float) – Maximum value relative to geoid to be considered as SL, in m, defaults to 10
candidate_area_thresh_km2 (float) – Minimum area beneath candidate_height_thresh_m to be considered for sea level assessment, in km^2. Defaults to 1
near_sealevel_thresh_m (float) – Filter out regions below this value, in metres above sea level. Defaults to 5
return_sealevel_as_zero (bool) – If True, subtracts that estimated sea level from the DEM, returning new height values with the estimated sea level set to 0 m. Necessary for calculating accurate iceberg heights. Defaults to False.
return_mask (bool) – Return the sea level mask rather than the masked DEM. Defaults to False.

Returns:

Filtered DEM as xarray DataArray

Return type:

DataArray

Returns terrain attributes as an xarray DataSet. Available attributes are as follows:

Slope

Aspect

Hillshade

Horizontal curvature

Vertical curvature

Mean curvature

Gaussian curvature

Unsphericity curvature

Minimal curvature

Maximal curvature

By default, computation of partial derivatives for geomorphometric variable calculation is performed following Florinsky (2009), who calculate the third- order partial derivative from a 5 x 5 window, which may be more appropriate for high-resolution DEMs with some amount of noise. The method parameter allows for the selection of a more traditional method using a second-order derivative from a 3 x 3 window, as outlined by Zevenbergen and Throrne (1987).

Parameters:

attribute – The attribute(s) to calculate, as a string or list.
method – Method to calculate geomorphometric parameters: “Florisnky” or “ZevenbergThorne”, defaults to “Florinsky”.
resolution – The DEM resolution. Calculated if empty, defaults to None
degrees – Outputs degrees if True, radians if False, defaults to True
hillshade_multidirectional – Calculates multidirectional hillshade following USGS/GDAL method (Mark, 1992). Defaults to False.
hillshade_altitude – Hillshade altitude in degrees (0-90°) from vertical, defaults to 45˚
hillshade_azimuth – Hillshade azimuth in degrees (0-360°) clockwise from North, defaults to 315
hillshade_z_factor – Vertical exaggeration factor, defaults to 1

Returns:

selected terrain attributes as a (rio)xarray DataSet

Return type:

DataSet

xarray .pdt accessor

Contents

xarray .pdt accessor#