Three different methods of specifying the output space frame are provided in LAS 7.0 (modules trancoord and remap).
Method 1:
The user defines the upper-left and lower-right corner coordinates of the area of interest in geographic coordinates. This forms a rectangle in geographic coordinates.
Implies
This rectangular space is projected into the output projection coordinate system. This usually results in a nonrectangular area.
The boundaries of this projected area are searched for minimum and maximum X and Y coordinates in the output projection coordinate system. This is performed by stepping along the output space frame at a given interval, sometimes resulting in approximate minimums and maximums. In most cases, the difference between the absolute and approximated minimum/maximums is negligible. This forms a minimum bounding rectangle in the output space of the area of interest.
The upper-left corner (the minimum X, maximum Y) is adjusted outward to the next X and Y multiples of the pixel size. This is an arbitrary step which simplifies the combining of images with different scales. It does not alter the internal image geometry; it only slightly adjusts the size of the image frame and the location of pixel (1,1).
The upper-left corner projection coordinate is assigned to image coordinate (1,1) in the output image.
Method 2:
The user defines:
The first coordinate given is adjusted to image coordinate (1,1) to get the minimum X and the maximum Y projection coordinate. The second coordinate pair given is the maximum X and the minimum Y coordinate. The output space is now defined. The pixel size is applied to the projection minimums and maximums to determine the number of lines and samples in the output space.
Method 3:
The user defines an output space projection coordinate at some image coordinate as in Method 2.
The user enters the number of output image lines and samples.
The coordinate entered is adjusted to image coordinate (1,1) to get the minimum X and the maximum Y projection coordinates.
The maximum X and minimum Y coordinates are calculated using the pixel size and the number of lines and samples from the minimum X and maximum Y projection coordinate.
Note that only the upper-left corner (the minimum X, maximum Y) of the output space is needed to grid the area to image coordinates. However, the lower-right corner (maximum X, minimum Y) is necessary to initialize framing information that is needed later in the process of registering an image.
