Merge pull request #32 from Kelvinrr/master

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# Comparing a USGSCSM and ISIS camera for Cassini ISS

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``` python

import pvl

import numpy as np

import os

import pandas as pd

import knoten

import csmapi

os.environ['ISISROOT'] = '/usgs/pkgs/isis3.8.0_RC1/install'

from pysis import isis

from pysis.exceptions import ProcessError

```

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## Make a CSM sensor model

Requires N1702360370_1.LBL and N1702360370_1.IMG in data directory

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``` python

fileName = 'data/N1702360370_1.LBL'

camera = knoten.csm.create_csm(fileName)

```

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## Ingest the image and spiceinit

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``` python

# Set the output location of the resulting .cub

cub_loc = os.path.splitext(fileName)[0] + '.cub'

try:

    isis.ciss2isis(from_=fileName, to=cub_loc)

except ProcessError as e:

    print(e.stderr)

try:

    isis.spiceinit(from_=cub_loc, shape='ellipsoid')

except ProcessError as e:

    print(e.stderr)

```

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## Define a function that compares ISIS and USGSCSM pixels

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``` python

def check_pixel(camera, cub, line, sample):

    """Compares ISIS and USGSCSM pixel.

    Takes an image coordinate, projects it to a ground point using ISIS, then projects

    the result back into an image coordinate using USGSCSM and computes the difference

    between image coordinates.

    """

    output = isis.campt(from_=cub, line=line, sample=sample)

    pvl_output = pvl.loads(output)

    bodyfixed = pvl_output['GroundPoint']['BodyFixedCoordinate']

    bodyfixed = np.asarray(bodyfixed.value) * 1000

    image_coord = camera.groundToImage(csmapi.EcefCoord(*bodyfixed))

    # (.5,.5) in CSM == (1,1) in ISIS, so we have to subtract (.5,.5) from the ISIS pixels

    line_diff = line - image_coord.line - .5

    sample_diff = sample - image_coord.samp - .5

    return line_diff, sample_diff

```

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## Get the total number of lines / samples

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``` python

isis_label = pvl.load(cub_loc)

n_samples = isis_label['IsisCube']['Core']['Dimensions']['Samples']

n_lines = isis_label['IsisCube']['Core']['Dimensions']['Lines']

```

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## Compare top left, top right, bottom left, bottom right, and center pixels using check_pixel

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``` python

pixels_dict = {'line' : [1,1,n_lines, n_lines, n_lines/2],

               'sample' : [1, n_samples, 1, n_samples, n_samples/2]}

pixels_df = pd.DataFrame.from_dict(pixels_dict)

pixels_df['line_diff'] = np.NaN

pixels_df['sample_diff'] = np.NaN

for idx, row in pixels_df.iterrows():

    pixels_df.iloc[idx]['line_diff'], pixels_df.iloc[idx]['sample_diff'] = check_pixel(camera, cub_loc, row['line'], row['sample'])

pixels_df

```

%% Output

         line  sample  line_diff  sample_diff

    0     1.0     1.0  -0.197283     4.530243

    1     1.0  1024.0  -0.213690     3.837590

    2  1024.0     1.0  -0.898897     4.538942

    3  1024.0  1024.0  -0.914839     3.846119

    4   512.0   512.0  -0.558596     4.191232

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``` python

```

    0     1.0     1.0   0.153039     0.906085

    1     1.0  1024.0   0.142231     0.326977

    2  1024.0     1.0  -0.425122     0.915083

    3  1024.0  1024.0  -0.435769     0.335980

    4   512.0   512.0  -0.142021     0.620648