Coverage for python/lsst/afw/geom/_calculateSipWcsHeader.py: 28%

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1# This file is part of afw. 

2# 

3# Developed for the LSST Data Management System. 

4# This product includes software developed by the LSST Project 

5# (https://www.lsst.org). 

6# See the COPYRIGHT file at the top-level directory of this distribution 

7# for details of code ownership. 

8# 

9# This program is free software: you can redistribute it and/or modify 

10# it under the terms of the GNU General Public License as published by 

11# the Free Software Foundation, either version 3 of the License, or 

12# (at your option) any later version. 

13# 

14# This program is distributed in the hope that it will be useful, 

15# but WITHOUT ANY WARRANTY; without even the implied warranty of 

16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

17# GNU General Public License for more details. 

18# 

19# You should have received a copy of the GNU General Public License 

20# along with this program. If not, see <https://www.gnu.org/licenses/>. 

21 

22 

23from lsst.geom import Extent2I, Box2D 

24from ._geom import SipApproximation, getPixelToIntermediateWorldCoords 

25from ._geom import makeTanSipMetadata 

26 

27__all__ = ("calculateSipWcsHeader",) 

28 

29 

30def calculateSipWcsHeader(wcs, order, bbox, spacing, header=None): 

31 """Generate a SIP WCS header approximating a given ``SkyWcs`` 

32 

33 Parameters 

34 ---------- 

35 wcs : `lsst.afw.geom.SkyWcs` 

36 World Coordinate System to approximate as SIP. 

37 order : `int` 

38 SIP order (equal to the maximum sum of the polynomial exponents). 

39 bbox : `lsst.geom.Box2I` 

40 Bounding box over which to approximate the ``wcs``. 

41 spacing : `float` 

42 Spacing between sample points. 

43 header : `lsst.daf.base.PropertyList`, optional 

44 Header to which to add SIP WCS keywords. 

45 

46 Returns 

47 ------- 

48 header : `lsst.daf.base.PropertyList` 

49 Header including SIP WCS keywords. 

50 

51 Examples 

52 -------- 

53 >>> header = calculateSipWcsHeader(exposure.getWcs(), 3, exposure.getBBox(), 20) 

54 >>> sipWcs = SkyWcs(header) 

55 """ 

56 transform = getPixelToIntermediateWorldCoords(wcs) 

57 crpix = wcs.getPixelOrigin() 

58 cdMatrix = wcs.getCdMatrix() 

59 crval = wcs.getSkyOrigin() 

60 gridNum = Extent2I(int(bbox.getWidth()/spacing + 0.5), int(bbox.getHeight()/spacing + 0.5)) 

61 

62 sip = SipApproximation(transform, crpix, cdMatrix, Box2D(bbox), gridNum, order) 

63 

64 md = makeTanSipMetadata(sip.getPixelOrigin(), crval, sip.getCdMatrix(), sip.getA(), sip.getB(), 

65 sip.getAP(), sip.getBP()) 

66 

67 if header is not None: 

68 header.combine(md) 

69 else: 

70 header = md 

71 

72 return header