PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2018-12-01 NOTE = "Explanation of relationship between the image coordinate and indexes of the data stored in the FITS file in this data set." END_OBJECT = TEXT END Relationship between the image coordinate and indexes of the data ================================================================= There are two kinds of data. The "l1b", "l2b", "l2c", and "geo" files store the value at the center of each pixel, Note that each pixel has the size with unit square, i.e., 1 x 1 pixel. FITS keywords for size of the image ----------------------------------- The following FITS header keywords are used to describe size of the image coordinate. These keywords are stored in the HDU of FITS file. NAXIS1 Number of pixels along the 1st axis or the horizontal axis that is same as +Ximg_fliprot axis described in SPICE IK for VCO UVI, IR1, IR2, and LIR instruments. NAXIS2 Number of pixels along the 2nd axis or the vertical axis that is same as +Yimg_fliprot axis described in SPICE IK for VCO UVI, IR1, IR2, and LIR instruments. Ranges of index for each axis ----------------------------- For the indexes of the data for the center of each pixel, the x- or horizontal indexes of the data, i, are 1, 2, ..., NAXIS1, and the y- or vertical indexes of the data, j, are 1, 2, ..., NAXIS2. All of the indexes of the data, i and j, are integer. Positions and indexing for each pixel ------------------------------------- The data at each index (i, j) that stores the center of each pixel corresponds to the data at position (i, j). All positions are integer. The diagram below shows the relationship between the positions in the image coordinate and indexes of the data. Upper-left Upper-right corner of pixel corner of pixel (i-0.5, j+0.5) (i+0.5, j+0.5) *-------------------* | | | | Notations: | center of pixel | | + | "+": center of each pixel. | (i, j) | "*": four corners of each pixel. | | | | *-------------------* (i-0.5, j-0.5) (i+0.5, j-0.5) Lower-left Lower-right corner of pixel corner of pixel Layout of the image for all pixels with the image coordinate ------------------------------------------------------------ The following diagram shows the layout of the image for all pixels with the image coordinate and the corresponding spacecraft axes in the image, where +Xsc, +Ysc, and +Zsc are axes of the spacecraft frame projected onto the image. Note that the -Xsc is the boresight direction of the all cameras. Please refer the latest VCO Frames kernel (FK) and the latest VCO Instrument kernels (IKs) provided in the 'VCO-V-SPICE-6-V1.0' data set for the details. |<---------------- NAXIS1+1 ---------------->| Upper-left corner Upper-right corner (0.5, NAXIS2+0.5) (NAXIS1+0.5, NAXIS2+0.5) *--------------------------------------------* --- | | ^ | | | | | | | | | | | | | | | | | | | + (i, j) | NAXIS2+1 | | | | | | | | | | | | | | | AXIS2, +Ysc | | | ^ | | V | *--------------------------------------------* --- | (0.5, 0.5) (NAIXS1+0.5, 0.5) | Lower-left corner Lower-right corner | x-----------> AXIS1, -Zsc -Xsc is into the page. Relationship between the image coordinate and the full-size image coordinate ---------------------------------------------------------------------------- In this section, relationship between the image coordinate described above and the full-size image coordinate is described. For UVI, IR1, and IR2 images, (except for IR2 image acquired with the 1.65-um filter), the size of the image is (128*m) x (128*n) where m, n are integer within [1, 8]. If (m, n) is equal to (8, 8), size of the image is 1024 x 1024, and the image is called "full-size image". If the region of interest (ROI) function is used for acquiring image, only the specified region is stored to the data recorder (DR) onboard, i.e., (m, n) is not equal to (8, 8), so the size of the data will be smaller. This function is used to reduce the size of image to be downlinked from the spacecraft. To describe the indexes in the full-size image coordinate (r, s) where r, s are integer within [1, 1024], the following FITS header keywords are used. P_POSLL[X,Y] horizontal and vertical indexes at the lower-left corner pixel of the image in the full-size coordinate. P_POSUR[X,Y] horizontal and vertical indexes at the upper-right corner pixel of the image in the full-size coordinate. The relation between indexes in the image coordinate (i, j) and indexes in the full-size image coordinate (r, s) for the same pixel is: (r, s) = (i + P_POSLLX - 1, j + P_POSLLY - 1). The following diagram shows the layout and the relationship between two coordinates. For simplicity, the below diagram shows only the relationship between indexes, and does not show the position of the pixels that is different with the diagram in the previous section. |<------------------ 1024 ------------------>| Upper-left corner Upper-right corner (1, 1024) (1024, 1024) +--------------------------------------------+ --- | | ^ | |<----- NAXIS1 ----->| | | | Upper-right corner | | | (P_POSURX, P_POSURY) | | | +--------------------+ --- | | | | | ^ | | | | | | | | | | + (r, s) | NAXIS2 | 1024 | | | | | | | | | V | | | +--------------------+ --- | | | Lower-left corner | | | (P_POSLLX, P_POSLLY) | | AXIS2, +Ysc | | | ^ | | V | +--------------------------------------------+ --- | (1, 1) (1024, 1) | Lower-left corner Lower-right corner | x-----------> AXIS1, -Zsc -Xsc is into the page. Note that IR2 image acquired with the 1.65-um filter is always same size, 520 x 520. For LIR images, the size of data is fixed to 328 x 248, so the image is always "full-size image". An example of the image coordinate for 1024 x 1024 image -------------------------------------------------------- This is an example of the image coordinate for the full-size (1024 x 1024) image of IR1, IR2, and UVI. If the region of interest (ROI) function is used for acquiring image, the size of the image will be smaller. Lower-left corner of the image coordinate. | | | | + | + | + | (1, 3) | (2, 3) | (3, 3) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 2.5) (1.5, 2.5) (2.5, 2.5) | | | | | | | | | | + | + | + | (1, 2) | (2, 2) | (3, 2) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 1.5) (1.5, 1.5) (2.5, 1.5) | | | | | | | | | | + | + | + | (1, 1) | (2, 1) | (3, 1) | | | ^ AXIS2, | | | | +Ysc | | | | *-------------------*-------------------*---------------- | (0.5, 0.5) (1.5, 0.5) (2.5, 0.5) | x-----------> AXIS1, -Zsc -Xsc is into the page Upper-left corner of the image coordinate. *-------------------*-------------------*---------------- (0.5, 1024.5) (1.5, 1024.5) (2.5, 1024.5) | | | | | | | | | | + | + | + | (1, 1024) | (2, 1024) | (3, 1024) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 1023.5) (1.5, 1023.5) (2.5, 1023.5) | | | | | | | | | | + | + | + | (1, 1023) | (2, 1023) | (3, 1023) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 1022.5) (1.5, 1022.5) (2.5, 1022.5) | | | | | | ^ AXIS2, | | | | +Ysc | + | + | + | | (1, 1022) | (2, 1022) | (3, 1022) | | | | | x-----------> AXIS1, -Zsc -Xsc is into the page Lower-right corner of the image coordinate. | | | + | + | + | (1022, 3) | (1023, 3) | (1024, 3) | | | | | | | | | | ----------------*-------------------*-------------------* (1022.5, 2.5) (1023.5, 2.5) (1024.5, 2.5) | | | | | | | | | + | + | + | (1022, 2) | (1023, 2) | (1024, 2) | | | | | | | | | | ----------------*-------------------*-------------------* (1022.5, 1.5) (1023.5, 1.5) (1024.5, 1.5) | | | | | | | | | + | + | + | (1022, 1) | (1023, 1) | (1024, 1) | | | | ^ AXIS2, | | | | +Ysc | | | | ----------------*-------------------*-------------------* | (1022.5, 0.5) (1023.5, 0.5) (1024.5, 0.5) | x-----------> AXIS1, -Zsc -Xsc is into the page Upper-right corner of the image coordinate. ----------------*-------------------*-------------------* (1022.5, 1024.5) (1023.5, 1024.5) (1024.5, 1024.5) | | | | | | | | | + | + | + | (1022, 1024) | (1023, 1024) | (1024, 1024) | | | | | | | | | | ----------------*-------------------*-------------------* (1022.5, 1023.5) (1023.5, 1023.5) (1024.5, 1023.5) | | | | | | | | | + | + | + | (1022, 1023) | (1023, 1023) | (1024, 1023) | | | | | | | | | | ----------------*-------------------*-------------------* (1022.5, 1022.5) (1023.5, 1022.5) (1024.5, 1022.5) | | | AXIS2, +Ysc | | | ^ | | | | + | + | + | | (1022, 1022) | (1023, 1022) | (1024, 1022) | | | | | | x-----------> AXIS1, -Zsc -Xsc is into the page An example of the image coordinate for 328 x 248 image ------------------------------------------------------ This is an example of the image coordinate for LIR image that always has the size 328 x 248. Lower-left corner of the image coordinate. | | | | + | + | + | (1, 3) | (2, 3) | (3, 3) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 2.5) (1.5, 2.5) (2.5, 2.5) | | | | | | | | | | + | + | + | (1, 2) | (2, 2) | (3, 2) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 1.5) (1.5, 1.5) (2.5, 1.5) | | | | | | | | | | + | + | + | (1, 1) | (2, 1) | (3, 1) | | | ^ AXIS2, | | | | +Ysc | | | | *-------------------*-------------------*---------------- | (0.5, 0.5) (1.5, 0.5) (2.5, 0.5) | x-----------> AXIS1, -Zsc -Xsc is into the page Upper-left corner of the image coordinate. *-------------------*-------------------*---------------- (0.5, 248.5) (1.5, 248.5) (2.5, 248.5) | | | | | | | | | | + | + | + | (1, 248) | (2, 248) | (3, 248) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 247.5) (1.5, 247.5) (2.5, 247.5) | | | | | | | | | | + | + | + | (1, 247) | (2, 247) | (3, 247) | | | | | | | | | *-------------------*-------------------*---------------- (0.5, 246.5) (1.5, 246.5) (2.5, 246.5) | | | | | | ^ AXIS2, | | | | +Ysc | + | + | + | | (1, 246) | (2, 246) | (3, 246) | | | | | x-----------> AXIS1, -Zsc -Xsc is into the page Lower-right corner of the image coordinate. | | | + | + | + | (326, 3) | (327, 3) | (328, 3) | | | | | | | | | | ----------------*-------------------*-------------------* (326.5, 2.5) (327.5, 2.5) (328.5, 2.5) | | | | | | | | | + | + | + | (326, 2) | (327, 2) | (328, 2) | | | | | | | | | | ----------------*-------------------*-------------------* (326.5, 1.5) (327.5, 1.5) (328.5, 1.5) | | | | | | | | | + | + | + | (326, 1) | (327, 1) | (328, 1) | | | | ^ AXIS2, | | | | +Ysc | | | | ----------------*-------------------*-------------------* | (326.5, 0.5) (327.5, 0.5) (328.5, 0.5) | x-----------> AXIS1, -Zsc -Xsc is into the page Upper-right corner of the image coordinate. ----------------*-------------------*-------------------* (326.5, 248.5) (327.5, 248.5) (328.5, 248.5) | | | | | | | | | + | + | + | (326, 248) | (327, 248) | (328, 248) | | | | | | | | | | ----------------*-------------------*-------------------* (326.5, 247.5) (327.5, 247.5) (328.5, 247.5) | | | | | | | | | + | + | + | (326, 247) | (327, 247) | (328, 247) | | | | | | | | | | ----------------*-------------------*-------------------* (326.5, 246.5) (327.5, 246.5) (328.5, 246.5) | | | AXIS2, +Ysc | | | ^ | | | | + | + | + | | (326, 246) | (327, 246) | (328, 246) | | | | | | x-----------> AXIS1, -Zsc -Xsc is into the page