SrtmConf#

class pycraf.pathprof.SrtmConf[source]#

Bases: MultiState

Provide a global state to adjust SRTM configuration.

By default, pycraf will look for SRTM ‘.hgt’ files (the terrain data) in the SRTMDATA environment variable. If this is not defined, the local directory (‘./’) is used for look-up. It is possible during run-time to change the directory where to look for ‘.hgt’ files with the SrtmConf manager:

from pycraf.pathprof import SrtmConf
SrtmConf.set(srtm_dir='/path/to/srtmdir')

This will also check, if all ‘.hgt’ files have the same size. If not an error is raised.

Alternatively, if only a temporary change of the config is desired, one can use SrtmConf as a context manager:

with SrtmConf.set(srtm_dir='/path/to/srtmdir'):
    # do stuff

Afterwards, the old settings will be re-established. It is also possible to allow downloading of missing ‘.hgt’ files:

SrtmConf.set(download='missing')

The default behavior is to not download anything (download='never'). There is even an option, to always force download (download='always').

The default download server will be server='nasa_v2.1'. One could also use the (very old) data (server='nasa_v1.0') or inofficial tiles from viewfinderpanorama (server='viewpano').

Of course, one can set several of these options simultaneously:

with SrtmConf.set(
        srtm_dir='/path/to/srtmdir',
        download='missing',
        server='viewpano'
        ):

    # do stuff

Last, but not least, it is possible to use different interpolation methods. The default method uses bi-linear interpolation (interp='linear'). One can also have nearest-neighbor (interp='nearest') or spline (interp='spline') interpolation. The two former internally use RegularGridInterpolator, the latter employs RectBivariateSpline that also allows custom spline degrees (kx and ky, default: 3) and smoothing factor (s, default: 0.). To change these use:

SrtmConf.set(interp='spline', spline_opts=(k, s))

We refer to RectBivariateSpline description for further information.

Two read-only attributes are present, tile_size (pixels) and hgt_res (m), which are automatically inferred from the tile data.

URLS:

Note: As of Spring 2021, NASA decided to put all SRTM data products behind a log-in page, such that automatic download ceases to work. If you prefer to use NASA tiles (over viewpano), please use their services, e.g., the Land Processes Distributed Active Archive Center

Attributes Summary

`download`
`hgt_res`
`interp`
`server`
`spline_opts`
`srtm_dir`
`tile_size`

Methods Summary

`hook`(**kwargs)	A hook which is called everytime when attributes are about to change.
`validate`(**kwargs)	This checks, if the provided inputs for `download` and `server` are allowed.

Attributes Documentation

download = 'never'#

hgt_res = 90.0#

interp = 'linear'#

server = 'viewpano'#

spline_opts = (3, 0)#

srtm_dir = '/home/vsts/work/1/srtm'#

tile_size = 1201#

Methods Documentation

classmethod hook(**kwargs)[source]#

A hook which is called everytime when attributes are about to change.

You should override this method if you want to enable pre-processing or monitoring of your attributes. For example, one could use this to react to attribute changes:

>>> from pycraf.utils import MultiState

>>> class MyState(MultiState):
...
...     _attributes = ('foo', 'bar')
...     foo = 1
...     bar = "guido"
...
...     @classmethod
...     def hook(cls, **kwargs):
...         if 'bar' in kwargs:
...             if kwargs['bar'] != cls.bar:
...                 print('{} about to change: {} --> {}'.format(
...                     'bar', kwargs['bar'], cls.bar
...                     ))
...                 # do stuff ...

>>> _ = MyState.set(bar="david")
bar about to change: david --> guido
>>> _ = MyState.set(bar="david")
>>> _ = MyState.set(bar="guido")
bar about to change: guido --> david

>>> with MyState.set(bar="david"):
...     pass
bar about to change: david --> guido
bar about to change: guido --> david

classmethod validate(**kwargs)[source]#

This checks, if the provided inputs for download and server are allowed. Possible values are:

download: ‘never’, ‘missing’, ‘always’
server: ‘viewpano’ # removed: ‘nasa_v2.1’, ‘nasa_v1.0’
interp: ‘nearest’, ‘linear’, ‘spline’
spline_opts: tuple(k, s) (k = degree, s = smoothing factor)