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vdemsetup(filv, indexfil, demtype, mapunits, dempxsz, demtile, elevunit, backelev, elevref)
| Name | Type | Caption | Length | Value range |
|---|---|---|---|---|
| FILV * | str | Name of the input vector file | 1 - | |
| INDEXFIL * | str | Name of the index file | 1 - | |
| DEMTYPE * | str | Format of the DEM file | 1 - 5 | PIX | TIF | JP2 |
| MAPUNITS | str | Map-projection units | 0 - | |
| DEMPXSZ * | List[float] | DEM resolution | 1 - 2 | |
| DEMTILE | List[int] | DEM tile dimensions (pixels, lines) | 0 - | |
| ELEVUNIT | str | Units of the elevation value | 0 - 7 | METER | FEET | US_FEET | DEFAULT |
| BACKELEV | List[float] | Value of the background elevation | 0 - | |
| ELEVREF | str | Vertical reference for elevation values | 0 - | MSL | ELLIPS | MATHMODEL |
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FILV
The name of the input PCIDSK (.pix) file that contains points, breaklines, and other vector information to use to generate a raster DEM. Typically, you use VDEMINGEST to generate the the input file.
INDEXFIL
The name of the index text file to create as output. The output file will contain information that defines each required raster DEM file (tile). This text file is read by VDEMINT to create the raster DEM files.
The file you specify must not exist and the file name must have a .txt file name extension. For more information on the format of the DEM-index file, follow the link to ORTHO under Related functions at the end of this topic.
DEMTYPE
The format of the output DEM files for VDEMINT to create.
Although all versions of the JPEG2000 compression lose some accuracy, it is usually minor. JPEG2000 compressed files can be 10 to 100 times smaller than the corresponding PIX or TIF files, depending on the option used: A, B, or C.
MAPUNITS
The output projection for the DEM.
If no value is specified for this parameter, the output projection defaults to that of the input file.
This parameter is optional.
DEMPXSZ
The x and y resolution of the DEM to produce. When you specify a single value, it is used for both x and y.
With LAT/LONG projections, the unit is DEGREES. With State Plane projections, the unit is FEET; for all other projections, the unit is METERS.
DEMTILE
The size of the output DEM file (tile), in pixels and lines.
The value you specify creates a sequence of files that cover the entire DEM extent. The files are created using the name of the provided in the input vector file, with the suffixes _0_0, _0_1, _1_1, and so on to indicate the row and column number of the tile.
When you specify a single value, it is used for both pixels and lines.
If no value is specified for this parameter, a single DEM file is created that is big enough to cover the entire DEM extent.
Tiles must be at least 1,000 pixels by 1,000 lines in size.
This parameter is optional.
ELEVUNIT
The units of the elevation.
If no value is specified for this parameter, or when the DEFAULT value is specified, the elevation units are transferred from the input file.
FEET is defined as 0.3048 meters (corresponding to International Feet); US_FEET is defined as 1200/3937 meters (corresponding to U.S. Survey Feet).
BACKELEV
The value of the background elevation (NoData) in the input elevation channel.
If no value is specified for this parameter, VDEMSETUP checks for ELEVATION_BACKGROUND or NO_DATA_VALUE metadata tags, first at the channel level, and then at the file level. If the value is neither specified nor found in the metadata, the default value of -32768 is applied.
This parameter is optional.
ELEVREF
The vertical reference for the elevation values in the source DEM, or for the constant ELFACTOR value, if it is used.
This option is used typically with satellites that have RPC models.
This option is used typically with aerial photography.
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VDEMSETUP creates an index file in text format (.txt), which describes the DEM files to generate with VDEMINT.
The following example shows an index file generated by VDEMSETUP for six tiles:
MAPUNITS SPAF 4100 D-02 DATATYPE 32R DBEC 1 BACKELEV -32768.000000 ELEVREF MATHMODEL ELEVUNIT FEET ELFACTOR 0.000000 1.000000 RES_XY 2.000000 2.000000 #Filename ULX ULY LRX LRY index_0_0.pix 1687702.000000 758178.000000 1691702.000000 754178.000000 index_0_1.pix 1691702.000000 758178.000000 1695702.000000 754178.000000 index_1_0.pix 1687702.000000 754178.000000 1691702.000000 750178.000000 index_1_1.pix 1691702.000000 754178.000000 1695702.000000 750178.000000 index_2_0.pix 1687702.000000 750178.000000 1691702.000000 746178.000000 index_2_1.pix 1691702.000000 750178.000000 1695702.000000 746178.000000
For more information on the format of the DEM-index file, follow the link to ORTHO under Related functions at the end of this topic.
Notes on JPEG2000 compression
If you specify the value of the DEMTYPE parameter as JP2, the DEM-raster files generated by VDEMINT will be compressed, often by a factor of 50 to 100. Not only is the JPEG2000 compression 'lossy', but it must be stored in 16-bit format, so that the vertical resolution of the elevation data is also scaled to the nearest centimeter (or inch) increment that will fit into a 16-bit range. In practice, the lossy compression and loss of vertical resolution is unnoticeable in the final orthorectified products.
VDEMSETUP automatically determines the vertical resolution based on several factors, including the total elevation range of the data and the pixel resolution of the raster DEM. Using the entry "ELFACTOR OFFSET, SCALE" in the index file, the actual elevation (in the unit specified for the ELEVUNIT parameter) can be computed from the 16-bit digital values stored in the raster DEM as:
elevation_value = scale * (DEM_pixel_value + offset)
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from pci.vdemingest import vdemingest from pci.vdemsetup import vdemsetup from pci.vdemint import vdemint POINTS = "points/*.txt" # x, y, and z points in text file CONTOURS = "" # no contours BREAKLIN = "breaklines/*.shp" # shapefile breaklines STRUCT3D = "" # no 3-D structure ELEVOPTS = "" # no special options ELEVRANG = [] # accept all elevations RIDGES = "" # no ridges VALLEYS = "" # no valleys CLIFFS = "" # no cliffs FILV = "vector.pix" # output vector file MAPUNITS = "" # default, projection from first file ELEVUNIT = "METER" # input points and breaklines in meters ELEVCONV = [] # no conversion (data already in meters) # ingest vector data vdemingest( POINTS, CONTOURS, BREAKLIN, STRUCT3D, ELEVOPTS, ELEVRANG, RIDGES, VALLEYS, CLIFFS, FILV, MAPUNITS, ELEVUNIT, ELEVCONV ) FILV = "vector.pix" INDEXFIL = "dem/index.txt" # index.txt and DEMs in folder dem DEMTYPE = "PIX" # PCIDSK 32-bit real output file for DEMs MAPUNITS = "" # default projection to that of FILV DEMPXSZ = [8,8] # output resolution of 8 meters in x,y for DEM data DEMTILE = [] # single DEM file (index.pix) covering entire extent ELEVUNIT = "METER" # no change BACKELEV = [] # default, -32,768 ELEVREF = "MATHMODEL" # DEM will be used with airphotos # create index.txt file ready for VDEMINT vdemsetup( FILV, INDEXFIL, DEMTYPE, MAPUNITS, DEMPXSZ, DEMTILE, ELEVUNIT, BACKELEV, ELEVREF ) FILE = "dem/index.txt" DBOC = [1] # index file contain only one channel DBOW = [] # generate entire DEM FILV = "vector.pix" # from VDEMINGEST DBVS = [] # automatically find vector segments VECTYP = [] # automatically determine vector types FLDNME = "" # no attributes MAXITER= [20] # maximum of 20 smoothing iterations MEMSIZE= [2000] # use 2,000 MB (2 GB) of memory # create the raster DEM (named index.pix) vdemint( FILE, DBOC, DBOW, FILV, DBVS, VECTYP, FLDNME, MAXITER, MEMSIZE )
In the preceding example, points and breakline vector data were ingested and stored in the file vector.pix and a raster DEM with a resolution of 8 meters created by VDEMINT. Examining the DEM, you realize that it should have been a DEM with a resolution of 2 meters; however, a DEM at a resolution of 2 meters will be 16 times the data volume, and a single DEM file will be many gigabytes. You decide to divide the DEM into 'tiles', each tile being a file 5,000 pixels by 5,000 lines (10 km x 10 km in extent), and use JPEG2000 compression on each tile to minimize the usage on disk.
You decide to put the tiles in a new folder named demjp2 on Drive D and use a Windows utility to create the folder.
Your first step is to use VDEMSETUP to create an index file describing the tiles you want, and then use VDEMINT to create the JPEG2000-compressed DEM tiles.
from pci.vdemsetup import vdemsetup from pci.vdemint import vdemint FILV = "vector.pix" INDEXFIL = "demjp2/index.txt" # index.txt and DEMs in folder demjp2 DEMTYPE = "JP2" # JPEG2000-compression format, default compression MAPUNITS = "" # default projection to that of FILV DEMPXSZ = [2,2] # output resolution of 2 meters in x,y for DEM data DEMTILE = [5000,5000] # DEM tiles each 5,000 pixels x 5,000 lines ELEVUNIT = "DEFAULT" # Elevation units from vector.pix BACKELEV = [] # default, -32,768 ELEVREF = "MATHMODEL" # DEM will be used with airphotos # create index.txt file ready for VDEMINT vdemsetup( FILV, INDEXFIL, DEMTYPE, MAPUNITS, DEMPXSZ, DEMTILE, ELEVUNIT, BACKELEV, ELEVREF ) FILE = "demjp2/index.txt" DBOC = [1] # output DEM in channel 1 DBOW = [] # generate entire DEM coverage FILV = "vector.pix" # from VDEMINGEST DBVS = [] # automatically find vector segments VECTYP = [] # automatically determine vector types FLDNME = "" # no attributes MAXITER= [20] # maximum of 20 smoothing iterations MEMSIZE= [2000] # use 2,000 MB (2 GB) of memory # create DEM tiles (index_0_0.jp2, index_0_1.jp2, ...) vdemint( FILE, DBOC, DBOW, FILV, DBVS, VECTYP, FLDNME, MAXITER, MEMSIZE )
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