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Diffstat (limited to 'doc/source/user.rst')
| -rw-r--r-- | doc/source/user.rst | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/doc/source/user.rst b/doc/source/user.rst index a163aa3..d3c2b2f 100644 --- a/doc/source/user.rst +++ b/doc/source/user.rst @@ -13,11 +13,7 @@ Requirements - Numpy 1.4 or later -- PyFITS - -- PyWCS - -- STWCS +- astropy 0.3 or later Coordinate representation ------------------------- @@ -34,7 +30,7 @@ contains functions to convert between (*ra*, *dec*) and (*x*, *y*, While any (*x*, *y*, *z*) triple represents a vector and therefore a location on the sky sphere, a distinction must be made between -normalized coordinates fall exactly on the unit sphere, and +normalized coordinates that fall exactly on the unit sphere, and unnormalized coordinates which do not. A normalized coordinate is defined as a vector whose length is 1, i.e.: @@ -47,10 +43,20 @@ assume that the vectors passed in are already normalized. If this is not the case, `stsci.sphere.vector.normalize_vector` can be used to normalize an array of vectors. -The library allows the user to work in either degrees or radians. All -methods that require or return an angular value have a `degrees` -keyword argument. When `degrees` is `True`, these measurements are in -degrees, otherwise they are in radians. +When not working in Cartesian vectors, the library allows the user to +work in either degrees or radians. All methods that require or return +an angular value have a `degrees` keyword argument. When `degrees` is +`True`, these measurements are in degrees, otherwise they are in +radians. + +.. warning:: + + Due to constraints in the precision of intersection calculations, + points on the sphere that are closer than :math:`2^{-32}` along a + Cartesian axis are automatically merged into a single point. This + prevents intersections from being missed due to floating point + rounding error. There is currently no implemented solution to + deal with points that need to be closer together. Spherical polygons ------------------ @@ -117,7 +123,7 @@ Creating spherical polygons - `SphericalPolygon.from_wcs`: Creates a polygon from the footprint of a FITS image using its WCS header keywords. Takes a FITS - filename or a `pyfits.Header` object. + filename or a `astropy.io.fits.Header` object. Operations on Spherical Polygons ```````````````````````````````` @@ -169,6 +175,9 @@ functions that are useful for dealing with them. - `intersects`: Determines if two great circle arcs intersect. +- `intersects_point`: Determines if a point is along the great circle + arc. + - `angle`: Calculate the angle between two great circle arcs. - `midpoint`: Calculate the midpoint along a great circle arc. |