nocam2map

This program will map project a raw instrument cube without a camera model. However, the lack of a camera model requires latitude/longitude information at each pixel in the raw cube. This must be facilitated through a latitude image and longitude image with the same size as the raw instrument cube.

The procedure to project the input cube is output driven. That is, we create an output map cube (as specified by the user) and at each output pixel, compute its projected latitude/longitude using the projection parameters. Using this coordinate we must search for that position in the two input cubes (latitude/longitude). If found, we will have a sub-pixel location that has a 1-1 correspondence with the raw instrument pixel. An interpolator (nearest neighbor, bilinear, or cubic convolution) is then used to compute a value for the output pixel.

Therefore the root of the problem is finding the latitude/longitude in the two input cubes as it is a 2-dimensional search. We do this by first creating two polynomial functions of a user-specified order (DEGREE), one for sample and one for line. These functions, f(lat,long) = sample and g(lat,long) = line, are dervied using a least-squares computation by collecting a sparse set of control points (line,samp)-to-(lat,long). The sparseness is controlled by the SINC and LINC. Unfortunately the polynomial is not accurate enough to supply the mapping to sub-pixel accuracy. The level of errors (between control points and the equations derived) can be written to the RESIDUAL file for examination.

To achieve sub-pixel accuracy, we use the polynomials to get us close (generally within 6 pixels). Using this estimated location, two affine transforms are computed by collecting a small 3x3 window of control points. These equations are used to further refine the estimated location. We iterate this process until our estimated sample/line is within an acceptable tolerance (TOLERANCE) of latitude/longitude values contained in the two cubes (LATCUB/LONCUB) or until the number of iterations is exceeded (ITERATIONS).

Defining the output map is controlled as follows:

• ProjectionName - Should be specified by the map file
• TargetName - Will be searched for in the FROM cube or can be specified by the user.
• EquatorialRadius and PolarRadius- Will be automatically computed from NAIF kernels or can be specified by the user.
• LatitudeType - Will be read from the map if available, otherwise will be set to the latitude type of the LATCUB
• LongitudeDirection - Will be read from the map if available, otherwise will be set to the longitude direction of the LONCUB
• LongitudeDomain - 0-360 by default.
• MinimumLatitude - Can be computed from the LATCUB, read from the map file or user specified.
• MaximumLatitude - Can be computed from the LATCUB, read from the map or user specified.
• MinimumLongitude - Can be computed from the LONCUB, read from the map or user specified.
• MaximumLongitude - Can be computed from the LONCUB, read from the map or user specified.
• Scale or PixelResolution - Can be computed¹ from the input, read from the map, or user specified in either meters/pixel (PixelResolution) or pixels/degree (Scale)

1To compute the scale we find the number of pixels from point (1, 1) to point (nsamples, nlines) in the input cube:
  sqrt[(nsamples-1)2 + (nlines-1)2]
 And the angle across this line:
  acos(cos(latitude_point1) * cos(latitude_point2) * cos(longitude_point1 - longitude_point2) + sin(latitude_point1) * sin(latitude_point2))
 The scale is equal to the number of pixels divided by the angle in pixels per degree.