Hide rubbersheeting scipy/astropy imports

Recent rubbersheeting changes added scipy and astropy imports which
are not otherwise needed. Due to isce2's eager import behavior this
causes errors when using unrelated functionality. We can fix this
by tucking these imports away inside their function definitions.

To reproduce:
`python3 -c "import isce; from stripmapApp import Insar"`
(without scipy/astropy installed)

components/isceobj/StripmapProc/runRubbersheet.py

@@ -6,7 +6,6 @@
 import isce
 import isceobj
 from osgeo import gdal
-from scipy import ndimage
 import numpy as np
 import os
 
@@ -24,6 +23,9 @@ def fill(data, invalid=None):
     Output:
         Return a filled array.
     """
+
+    from scipy import ndimage
+
     if invalid is None: invalid = np.isnan(data)
 
     ind = ndimage.distance_transform_edt(invalid,
@@ -35,6 +37,8 @@ def fill(data, invalid=None):
 def mask_filter(denseOffsetFile, snrFile, band, snrThreshold, filterSize, outName):
     #masking and Filtering
 
+    from scipy import ndimage
+
     ##Read in the offset file
     ds = gdal.Open(denseOffsetFile + '.vrt', gdal.GA_ReadOnly)
     Offset = ds.GetRasterBand(1).ReadAsArray()

components/isceobj/StripmapProc/runRubbersheetAzimuth.py

@@ -9,14 +9,14 @@
 import isce
 import isceobj
 from osgeo import gdal
-from scipy import ndimage
-from astropy.convolution import convolve
 import numpy as np
 import os
 
 def mask_filterNoSNR(denseOffsetFile,filterSize,outName):
     # Masking the offsets with a data-based approach
 
+    from scipy import ndimage
+
     # Open the offsets
     ds = gdal.Open(denseOffsetFile+'.vrt',gdal.GA_ReadOnly)
     off_az = ds.GetRasterBand(1).ReadAsArray()
@@ -79,6 +79,9 @@ def mask_filterNoSNR(denseOffsetFile,filterSize,outName):
 
 
 def off_masking(off,filterSize,thre=2):
+
+    from scipy import ndimage
+
     # Define the mask to fill the offsets
     vram = ndimage.median_filter(off.real, filterSize)
     vazm = ndimage.median_filter(off.imag, filterSize)
@@ -112,6 +115,8 @@ def fill(data, invalid=None):
 def mask_filter(denseOffsetFile, snrFile, band, snrThreshold, filterSize, outName):
     #masking and Filtering
 
+    from scipy import ndimage
+
     ##Read in the offset file
     ds = gdal.Open(denseOffsetFile + '.vrt', gdal.GA_ReadOnly)
     Offset = ds.GetRasterBand(band).ReadAsArray()
@@ -155,6 +160,8 @@ def mask_filter(denseOffsetFile, snrFile, band, snrThreshold, filterSize, outNam
 
 def fill_with_smoothed(off,filterSize):
 
+    from astropy.convolution import convolve
+
     off_2filt=np.copy(off)
     kernel = np.ones((filterSize,filterSize),np.float32)/(filterSize*filterSize)
     loop = 0

components/isceobj/StripmapProc/runRubbersheetRange.py

@@ -9,15 +9,14 @@
 import isce
 import isceobj
 from osgeo import gdal
-from scipy import ndimage
 import numpy as np
 import os
-from astropy.convolution import convolve
-
 
 def mask_filterNoSNR(denseOffsetFile,filterSize,outName):
     # Masking the offsets with a data-based approach
 
+    from scipy import ndimage
+
     # Open the offsets
     ds = gdal.Open(denseOffsetFile+'.vrt',gdal.GA_ReadOnly)
     off_az = ds.GetRasterBand(1).ReadAsArray()
@@ -78,6 +77,9 @@ def mask_filterNoSNR(denseOffsetFile,filterSize,outName):
     return 
 
 def off_masking(off,filterSize,thre=2):
+
+    from scipy import ndimage
+
     vram = ndimage.median_filter(off.real, filterSize)
     vazm = ndimage.median_filter(off.imag, filterSize)
 
@@ -100,6 +102,8 @@ def fill(data, invalid=None):
     Output:
         Return a filled array.
     """
+    from scipy import ndimage
+
     if invalid is None: invalid = np.isnan(data)
 
     ind = ndimage.distance_transform_edt(invalid,
@@ -109,6 +113,8 @@ def fill(data, invalid=None):
 
 def fill_with_smoothed(off,filterSize):
 
+    from astropy.convolution import convolve
+
     off_2filt=np.copy(off)
     kernel = np.ones((filterSize,filterSize),np.float32)/(filterSize*filterSize)
     loop = 0
@@ -131,6 +137,8 @@ def fill_with_smoothed(off,filterSize):
 def mask_filter(denseOffsetFile, snrFile, band, snrThreshold, filterSize, outName):
     #masking and Filtering
 
+    from scipy import ndimage
+
     ##Read in the offset file
     ds = gdal.Open(denseOffsetFile + '.vrt', gdal.GA_ReadOnly)
     Offset = ds.GetRasterBand(band).ReadAsArray()
@@ -236,6 +244,8 @@ def resampleOffset(maskedFiltOffset, geometryOffset, outName):
 
 def runRubbersheetRange(self):
 
+    from scipy import ndimage
+
     if not self.doRubbersheetingRange:
         print('Rubber sheeting in azimuth not requested ... skipping')
         return