dskw02_c |

Table of contents## Proceduredskw02_c ( DSK, write type 2 segment ) void dskw02_c ( SpiceInt handle, SpiceInt center, SpiceInt surfid, SpiceInt dclass, ConstSpiceChar * frame, SpiceInt corsys, ConstSpiceDouble corpar[], SpiceDouble mncor1, SpiceDouble mxcor1, SpiceDouble mncor2, SpiceDouble mxcor2, SpiceDouble mncor3, SpiceDouble mxcor3, SpiceDouble first, SpiceDouble last, SpiceInt nv, ConstSpiceDouble vrtces[][3], SpiceInt np, ConstSpiceInt plates[][3], ConstSpiceDouble spaixd[], ConstSpiceInt spaixi[] ) ## AbstractWrite a type 2 segment to a DSK file. ## Required_ReadingDAS DSK NAIF_IDS ## KeywordsDAS DSK FILES PLATE TOPOGRAPHY ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- handle I Handle assigned to the opened DSK file. center I Central body ID code. surfid I Surface ID code. dclass I Data class. frame I Reference frame. corsys I Coordinate system code. corpar I Coordinate system parameters. mncor1 I Minimum value of first coordinate. mxcor1 I Maximum value of first coordinate. mncor2 I Minimum value of second coordinate. mxcor2 I Maximum value of second coordinate. mncor3 I Minimum value of third coordinate. mxcor3 I Maximum value of third coordinate. first I Coverage start time. last I Coverage stop time. nv I Number of vertices. vrtces I Vertices. np I Number of plates. plates I Plates. spaixd I Double precision component of spatial index. spaixi I Integer component of spatial index. SPICE_DSK_ANGMRG P Angular round-off margin. SPICE_DSK_GENCLS P General surface DSK class. SPICE_DSK_SVFCLS P Single-valued function DSK class. SPICE_DSK_NSYPAR P Maximum number of coordinate system parameters in a DSK descriptor. SPICE_DSK02_MAXCGR P Maximum DSK type 2 coarse voxel count. SPICE_DSK02_MAXPLT P Maximum DSK type 2 plate count. SPICE_DSK02_MAXVOX P Maximum DSK type 2 voxel count. SPICE_DSK02_MAXVRT P Maximum DSK type 2 vertex count. ## Detailed_Inputhandle is the DAS file handle associated with a DSK file. The file must be open for write access. center is the ID code of the body whose surface is described by the input plate model. `center' refers to an ephemeris object. surfid is the ID code of the surface described by the input plate model. Multiple surfaces (for example, surfaces having different resolutions) may be associated with a given body. dclass is the data class of the input data set. See the header file SpiceDSK.h for values and meanings. frame is the name of the reference frame with respect to which the input data are expressed. corsys is the coordinate system in which the spatial coverage of the input data is expressed. `corsys' is an integer code. See the header file SpiceDSK.h for values and meanings. corpar is an array of parameters associated with the input coordinate system. For latitudinal and rectangular coordinates, `corpar' is ignored. For planetodetic coordinates, the contents of `corpar' are: Element Contents --------- ----------------------------------- corpar[0] Equatorial radius of reference spheroid. corpar[1] Flattening coefficient. The polar radius of the reference spheroid is given by corpar[0] * ( 1 - corpar[1] ) corpar[2]... corpar[SPICE_DSK_NSYPAR-1] Unused. mncor1, mxcor1, mncor2, mxcor2, mncor3, mxcor3 are, respectively, lower and upper bounds of each of the coordinates of the input data, where the coordinate system is defined by `corsys' and `corpar'. These bounds define the region for which the segment provides data. Distance units are km. Angular units are radians. The interpretation of these bounds depends on the data class; see `dclass' above. Single-valued surfaces ---------------------- If the segment has data class SPICE_DSK_SVFCLS (see SpiceDSK.h), the segment defines a surface as a single-valued function of its domain coordinates: for example, it may define the radius of the surface as a function of planetocentric longitude and latitude. In this case, the input data must cover a rectangle in dimensions 1 and 2 of the input coordinate system: the set of points R = { (x,y): mncor1 < x < mxcor1; mncor2 < y < mxcor2 } must be completely covered by the input data. In other words, for each point (x,y) of R, there must be some plate containing a point whose first two coordinates are (x,y). The plate set may extend beyond the coordinate range defined by the bounds on the domain. Normally for single-valued surfaces, `mncor3' and `mxcor3' are the minimum and maximum values of the function attained on the domain. General surfaces ---------------- If the segment has data class SPICE_DSK_GENCLS (see SpiceDSK.h), the segment simply contains a collection of plates: no guarantees are made about the topology of the surface. The coordinate bounds simply indicate the spatial region for which the segment provides data. Note that shapes of small bodies such as asteroids and comet nuclei may fall into the "general surface" category. Surface features such as cliffs, caves, and arches can prevent a surface from being represented as a single-valued function of latitude and longitude, for example. Longitude interpretation and restrictions ----------------------------------------- The following rules apply to longitudes provided in the arguments mncor1 mxcor1 All angles have units of radians. The tolerance SPICE_DSK_ANGMRG is used for the comparisons shown below. 1) Longitudes must be in the range -2*pi : 2*pi Values that are out of range by no more than SPICE_DSK_ANGMRG are bracketed to be in range. 2) It is acceptable for the longitude bounds to be equal or out of order. If mxcor1 < mncor1 - then either `mxcor1' is treated by the DSK subsystem as though it were mxcor1 + 2*pi, or `mncor1' is treated as mncor1 - 2*pi: whichever shift puts the bounds in the allowed range is made. The input longitude bounds must not be equal. If the lower bound is greater than the upper bound, the difference between the bounds must not be an integer multiple of 2*pi. Aside from any small changes made to move the input values of `mncor1' or `mxcor1' into range, the values are stored in the DSK segment as is. 3) `mxcor1' must not exceed `mncor1' by more than 2*pi. Values that are out of range by no more than SPICE_DSK_ANGMRG are bracketed to be in range. first, last are the endpoints of the time interval over which this data set is applicable. These times are expressed as seconds past J2000 TDB. nv is the number of vertices belonging to the plate model. vrtces is an array of coordinates of the vertices. The ith vertex occupies elements [i-1][0:2] of this array. np is the number of plates in the plate model. plates is an array representing the plates of the model. The elements of `plates' are vertex indices. The vertex indices of the ith plate occupy elements [i-1][0:2] of this array. spaixd, spaixi are, respectively, the double precision and integer components of the spatial index of the segment. It is strongly recommended that the helper routine dskmi2_c be used to create these arrays. See the -Examples section below. ## Detailed_OutputNone. This routine operates by side effects. ## ParametersSee the header files SpiceDSK.h SpiceDtl.h for declarations of parameters that may be used as inputs to this routine, or that may be used to declare bounds of arrays which are arguments of this routine. ## Exceptions1) If the reference frame name `frame' could not be mapped to an ID code, the error SPICE(FRAMEIDNOTFOUND) is signaled by a routine in the call tree of this routine. 2) If the segment stop time precedes the start time, the error SPICE(TIMESOUTOFORDER) is signaled by a routine in the call tree of this routine. 3) If an input longitude value is outside the range [ -2*pi - SPICE_DSK_ANGMRG, 2*pi + SPICE_DSK_ANGMRG ] the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. Longitudes outside of the range by a smaller amount than SPICE_DSK_ANGMRG will be truncated to lie in the interval [-2*pi, 2*pi]. 4) If the absolute value of the difference between the input maximum longitude and the minimum longitude is more than 2*pi + SPICE_DSK_ANGMRG, the error SPICE(INVALIDLONEXTENT) will be signaled by a routine in the call tree of this routine. If either longitude bound exceeds the other by an amount between 2*pi and 2*pi+SPICE_DSK_ANGMRG, the larger value will be truncated to the smaller value plus 2*pi. 5) If an input latitude value is outside the range [ -pi/2 - SPICE_DSK_ANGMRG, pi/2 + SPICE_DSK_ANGMRG ] the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. Latitudes outside of the range by a smaller amount than SPICE_DSK_ANGMRG will be truncated to lie in the interval [-pi/2, pi/2]. 6) If the coordinate system is latitudinal and the lower radius bound is negative, or if the upper radius bound is non-positive, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 7) If the coordinate system is latitudinal or planetodetic and the bounds of the radius or altitude coordinate are out of order, the error SPICE(BOUNDSOUTOFORDER) is signaled by a routine in the call tree of this routine. 8) If the coordinate system is latitudinal or planetodetic and the lower and upper bounds of the longitude, latitude, radius or altitude coordinate, respectively, are equal, the error SPICE(ZEROBOUNDSEXTENT) is signaled by a routine in the call tree of this routine. If the lower longitude bound is greater than the upper bound, and if the difference between the bounds is an integer multiple of 2*pi, the same error is signaled. 9) If the coordinate system is planetodetic and the input equatorial radius is non-positive, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 10) If the coordinate system is planetodetic and the input flattening coefficient is greater than or equal to 1, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 11) If the coordinate system is planetodetic, and if the minimum altitude is less than the maximum of 2 2 { -(B / A), -(A / B) } where A and B are the semi-major and semi-minor axis lengths of the reference ellipsoid, the error SPICE(DEGENERATESURFACE) is signaled by a routine in the call tree of this routine. 12) If the coordinate system is rectangular and any coordinate lower bound is greater than or equal to the corresponding upper bound, the error SPICE(BOUNDSOUTOFORDER) is signaled by a routine in the call tree of this routine. 13) If the coordinate system code is not recognized, the error SPICE(NOTSUPPORTED) is signaled by a routine in the call tree of this routine. 14) If any vertex index belonging to an input plate is outside of the range 1:nv, the error SPICE(BADVERTEXINDEX) is signaled by a routine in the call tree of this routine. 15) If `nv' is less than 1 or greater than SPICE_DSK02_MAXVRT, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 16) If `np' is less than 1 or greater than SPICE_DSK02_MAXPLT, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 17) If any voxel grid extent is less than 1 or greater than SPICE_DSK02_MAXVOX, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 18) If the voxel count is greater than SPICE_DSK02_MAXVOX, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 19) If the coarse voxel count is less than 1 or greater than SPICE_DSK02_MAXCGR, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 20) If the coarse voxel scale is less than 1 or more than the cube root of the fine voxel count, the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call tree of this routine. 21) If the cube of the coarse voxel scale does not divide the fine voxel count evenly, the error SPICE(INCOMPATIBLESCALE) is signaled by a routine in the call tree of this routine. 22) If the input data class is not recognized, the error SPICE(NOTSUPPORTED) is signaled by a routine in the call tree of this routine. 23) If an error occurs while writing the segment to the output DSK file, the error is signaled by a routine in the call tree of this routine. 24) If the `frame' input string pointer is null, the error SPICE(NULLPOINTER) is signaled. 25) If the `frame' input string has zero length, the error SPICE(EMPTYSTRING) is signaled. ## FilesSee argument `handle'. ## ParticularsThis routine writes a type 2 segment to a DSK file that has been opened for write access. Users planning to create DSK files should consider whether the SPICE DSK creation utility MKDSK may be suitable for their needs. This routine is supported by the routines dskmi2_c and dskrb2_c dskmi2_c simplifies use of this routine by creating the "spatial index" arrays required as inputs by this routine. dskrb2_c computes bounds on the third coordinate of the input plate set. Spatial Indexes =============== A spatial index is a group of data structures that facilitates rapid high-level computations involving sets of plates. The data structures created by this routine are aggregated into arrays of type SpiceInt and type SpiceDouble. Voxel grids =========== A key geometric computation---probably the most important, as it serves as a foundation for other high-level computations---is finding the intersection of a ray with the plate set. DSK type 2 segments use data structures called "voxel grids" as part of their indexing mechanism. There is a "coarse grid": a box that completely encloses a DSK type 2 segment's plate set, and which is composed of identically-sized cubes called "coarse voxels." Each coarse voxel in composed of smaller cubes called "fine voxels." When the term "voxel" is used without qualification, it refers to fine voxels. Type 2 DSK segments contain data structures that associate plates with the fine voxels intersected by those plates. These structures enable the type 2 DSK software to rapidly find plates in a given region of space. Voxel scales ============ There are two voxel scales: - The coarse voxel scale is the integer ratio of the edge length of a coarse voxel to the edge length of a fine voxel - The fine voxel scale is the double precision ratio of the edge length of a fine voxel to the average extent of the plates in the input plate set. "Extents" of a plate are the absolute values of the differences between the respective maximum and minimum X, Y, and Z coordinates of the plate's vertices. Voxel scales determine the resolution of the voxel grid. Voxel scales must be chosen to satisfy size constraints and provide reasonable plate lookup performance. The following considerations apply to spatial indexes of type 2 DSK segments: 1) The maximum number of coarse voxels is fixed at SPICE_DSK02_MAXCGR (declared in SpiceDSK.h). 2) If there are too few fine voxels, the average number of plates per fine voxel will be very large. This largely negates the performance improvement afforded by having an index. Also, the number of plates per voxel may exceed limits imposed by DSK subroutines that use static arrays. 3) If there are too many fine voxels, the average number of voxels intersected by a given plate may be too large for all the plate-voxel associations to be stored. In addition, the time needed to examine the plate lists for each voxel (including the empty ones) may become quite large, again negating the value of the index. In many cases, voxel scales yielding optimum performance must be determined by experiment. However, the following heuristics can provide reasonable starting values: Let `np' be the number of plates. Let `fs' be the fine voxel scale. Then a reasonable value of `fs' may be (0.25) fs = np / 8. In general, `fs' should not smaller than 1. ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Create a three-segment DSK file using plate model data for Phobos. Use latitudinal, rectangular, and planetodetic coordinates in the respective segments. This is not a realistic example, but it serves to demonstrate use of the supported coordinate systems. Use the DSK kernel below to provide, for simplicity, the input plate and vertex data. The selected input file has one segment. phobos_3_3.bds Example code begins here. /. Program dskw02_ex1 Example program for ## RestrictionsNone. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) ## Version-CSPICE Version 1.0.1, 10-AUG-2021 (JDR) Edited the header to comply with NAIF standard. Added example's output. -CSPICE Version 1.0.0, 04-APR-2017 (NJB) Based on Alpha DSK version 2.0.0, 13-MAY-2010 (NJB). Caution: this routine's argument list has been changed. ## Index_Entrieswrite a type 2 DSK segment |

Fri Dec 31 18:41:05 2021