Math

Functions

arctan2(y, x)

Element-wise arc tangent of y/x choosing the quadrant correctly.

cos(obj)

Element-wise cosine of an Image or ImageCollection.

log(obj)

Element-wise natural log of an Image or ImageCollection.

log2(obj)

Element-wise base 2 log of an Image or ImageCollection.

log10(obj)

Element-wise base 10 log of an Image or ImageCollection.

normalized_difference(x, y)

Normalized difference helper function for computing an index such as NDVI.

sin(obj)

Element-wise sine of an Image or ImageCollection.

sqrt(obj)

Element-wise square root of an Image or ImageCollection.

tan(obj)

Element-wise tangent of an Image or ImageCollection.

arctan2(y, x)[source]

Element-wise arc tangent of y/x choosing the quadrant correctly.

The quadrant (i.e., branch) is chosen so that arctan2(y, x) is the signed angle in radians between the ray ending at the origin and passing through the point (1,0), and the ray ending at the origin and passing through the point (x, y). (Note the role reversal: the “y-coordinate” is the first function parameter, the “x-coordinate” is the second.) By IEEE convention, this function is defined for x = +/-0 and for either or both of y and x = +/-inf (see Notes for specific values).

Parameters
  • y (Int, Float, Image, ImageCollection) – y-coordinates

  • x (Int, Float, Image, ImageCollection) – x-coordinates

Returns

x – Angle(s) in radians, in the range [-pi, pi], of the type that results from broadcasting y to x, (except Int is promoted to Float)

Return type

Float, Image, ImageCollection

Notes

arctan2 is identical to the atan2 function of the underlying C library. The following special values are defined in the C standard: 1

y

x

arctan2(y,x)

+/- 0

+0

+/- 0

+/- 0

-0

+/- pi

> 0

+/-inf

+0 / +pi

< 0

+/-inf

-0 / -pi

+/-inf

+inf

+/- (pi/4)

+/-inf

-inf

+/- (3*pi/4)

Note that +0 and -0 are distinct floating point numbers, as are +inf and -inf.

References

1

ISO/IEC standard 9899:1999, “Programming language C.”

cos(obj)[source]

Element-wise cosine of an Image or ImageCollection.

Can also be used with Int and Float types.

log(obj)[source]

Element-wise natural log of an Image or ImageCollection.

Can also be used with Int and Float types.

log2(obj)[source]

Element-wise base 2 log of an Image or ImageCollection.

Can also be used with Int and Float types.

log10(obj)[source]

Element-wise base 10 log of an Image or ImageCollection.

Can also be used with Int and Float types.

normalized_difference(x, y)[source]

Normalized difference helper function for computing an index such as NDVI.

Example

>>> import descarteslabs.workflows as wf
>>> col = wf.ImageCollection.from_id("landsat:LC08:01:RT:TOAR")
>>> nir, red = col.unpack_bands(["nir", "red"])
>>> ndvi = wf.normalized_difference(nir, red)
sin(obj)[source]

Element-wise sine of an Image or ImageCollection.

Can also be used with Int and Float types.

sqrt(obj)[source]

Element-wise square root of an Image or ImageCollection.

Can also be used with Int and Float types.

tan(obj)[source]

Element-wise tangent of an Image or ImageCollection.

Can also be used with Int and Float types.