GRDPNT -- Point Coverage Gridding

Given a set of points stored in a vector segment, a raster image is generated where each grey level corresponds to the attribute value of the closest point.

NOTE: If vectors are not stored in PIXEL coordinates, then the database georeferencing and vector georeferencing must match.

See Also: GRDPIN, GRDPOL, GRDVEC, GRDINT, NUMREAD, NUMWRIT

PARAMETERS

GRDPNT is controlled by the following global parameters: 

Name     Prompt                                  Count     Type
FILE     Database File Name                      1-64      Char
DBVS     Database Vector Segment                 1         Int
DBOC     Database Output Channel List            1         Int
FLDNME   Field name to use for Elevation         0-64      Char

FILE

Specifies the name of the PCIDSK database file from which the vector segment point data is read and to which the rasterized output is written. 

 EASI>FILE="filespec"

DBVS

Specifies the vector segment which stores point data. The vector segment may contain both point and line information. However, for the purposes of this program, only the point data and its associated attribute values are used. 

 EASI>DBVS=i

DBOC

Specifies the output database channel to store the rasterized image. 

 EASI>DBOC=i

FLDNME

Specifies the field to be used as the elevation value. If the FLDNME parameter is left blank it will be defaulted to "Attribute". If the FLDNME parameter is "ZCOORD" then the actual Z-coordinate of the vectors will be used. 

 EASI>FLDNME =               | Use attribute field named "Attribute"
 EASI>FLDNME = "zcoord"      | Use z-coordinate of vectors
 EASI>FLDNME = "Elevation"   | Use field called "Elevation"
 EASI>FLDNME = "Elev"        | Will also work for "Elevation"
The names are not case sensitive, and the entire name need not be specified. If more than one match exists, the first one will be used.

DETAILS

GRDPNT uses as input the point data structures within the specified vector segment file (DBVS) of the database FILE. An output channel (DBOC) is created in which the area of any given region represents all pixels that are closer to the attribute location that defines the region than to any other attribute location as specified by DBVS.

If an attribute value is out of range for the DBOC data type, its value is truncated to the minimum or maximum allowable value. GRDPNT tallies the number of attributes requiring truncation measures and reports this information to the user. If all attributes were truncated, the wrong DBOC was likely to have been specified. Run CDL to check the data type for DBOC (8-bit, 16-bit signed or unsigned, or 32-bit real) and run VECREP to check that the attribute values are within the range for the DBOC data type. If only a few attributes were truncated, they too can be checked as outlined. However, they are more likely to be the result of either digitizing errors and/or deliberate special cases.

If the units for storing vector data are not "PIXEL", but are "UTM" or any other type, then the database must be georeferenced, using the GEOSET program, prior to running GRDPNT. The units for georeferencing must be the same as were used in collecting the vector data. Run the GEOREP program to print the current georeferencing information for the database.

Vector segments can be created using the VECDIG or the VED program. Alternatively, an appropriate vector segment file can be created with RTV (option "POINT" or "BOTH") using a thematic image as input.

As of version 6.0, each vector may now contain more than one attribute field. The FLDNME parameter is used to select which attribute field will be used.

EXAMPLE

Objective:

Using USGS landuse/landcover channel 6 of irvine.pix as input, generate a vector segment of point information that can be used as input to run GRDPNT.

Procedure:

Filter the USGS landuse/landcover channel 6 to ensure that a reasonable number of points are generated. 

 EASI>FILE="irvine.pix"  | database filename
 EASI>DBIC=6             | database input channel  
 EASI>DBOC=7             | database output channel
 EASI>FLSZ=5,5           | filter size
 EASI>THINLINE = "OFF"   | Do not preserve thin lines
 EASI>MASK=              | filter entire image
 EASI>KEEPVALU=          | filter all values
 EASI>RUN FMO
Generate a vector segment containing one point location (centroid) for each coverage (polygon) of the filtered classification image. 

 EASI>FILE="irvine.pix"  | database filename
 EASI>DBIC=7             | database input channel  
 EASI>DBIW=              | database input window
 EASI>DBSN="Centroid"    | database segment name
 EASI>DBSD="Example"     | database segment descriptor
 EASI>POLYINFO="POINTS"  | point generation
 EASI>BORDER="OFF"       | set border specification off
 EASI>CONTINT=           | not needed
 EASI>RUN RTV
Direct display of the vector segment file to the terminal (only a portion will be displayed, as such files are generally very large). 

 EASI>FILE="irvine.pix"  | database filename
 EASI>DBVS=LASC          | database vector segment
 EASI>REPORT="TERM"      | report device
 EASI>RUN VECREP
Terminal output: 

 VECREP  Vector Segment Report      V5.1 EASI/PACE  15:45 09-Oct-92
 
 irvine.pix                 [S   11PIC     512P     512L] 14-Aug-90

 33:Centroid  Type:116 [Vectors/Polygons]   Update: 15:39 09-Oct-92
 Contents: Example
 Length:         6.0 Kbytes     Units: PIXEL        Structures: 250
 Bounds: (     0.000 X,      0.000 Y), (   512.000 X,    512.000 Y)

 Structure     1   Type: Point    Group:    0  Attribute:        21

        15.500 X,            0.500 Y
 
 Structure     2   Type: Point    Group:    0  Attribute:        32

        48.500 X,            0.500 Y
 
 Structure     3   Type: Point    Group:    0  Attribute:        32

       208.500 X,            0.500 Y
Alternatively, the vectors can be can be displayed graphically using the IVV program. 

 EASI>FILE="irvine.pix"   | database filename
 EASI>DBVS=LASC           | database vector segment 
 EASI>VDOB=1              | graphic plane for display
 EASI>DBVW=               | window of interest in vector file
 EASI>VDOW=               | window of graphic display for use
 EASI>PCLG=1              | graphic plane to be precleared
 EASI>RUN IVV
Generate rasterized regions using the vector point data of LASC as the seeds for growing the regions. 

 EASI>FILE="irvine.pix"   | database filename
 EASI>DBVS=LASC           | vector segment number
 EASI>DBOC=8              | database output channel
 EASI>FLDNME=                 | Use attribute   
 EASI>RUN GRDPNT
Print a 15x15 numeric window of the raster output to the terminal. 

 EASI>FILE="irvine.pix"   | database filename
 EASI>DBIC=8              | channel of interest
 EASI>DBIW=355,490,15,15  | window of interest within channel
 EASI>REPORT="TERM"       | report device
 EASI>RUN NUM

 
 NUM     Database Numeric Window    V5.1 EASI/PACE  15:54 09-Oct-92

 irvine.pix                 [S   11PIC     512P     512L] 14-Aug-90
 8 [ 8U] GRDPNT  Region growing complete                  09-Oct-92

 Offset: (     355,     490)  Size: (      15,      15)
 
          3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
          5   5   5   5   6   6   6   6   6   6   6   6   6   6   7
          6   7   8   9   0   1   2   3   4   5   6   7   8   9   0
       +-----------------------------------------------------------
    491| 76  76  76  76  76  76  76  76  76  76  76  76  76  17  17
    492| 12  76  76  76  76  76  76  76  76  76  76  76  17  17  17
    493| 12  12  76  76  76  76  76  76  76  76  76  76  17  17  17
    494| 12  12  12  12  76  76  76  76  76  76  76  17  17  17  17
    495| 12  12  12  12  12  12  76  76  76  76  17  17  17  17  17
    496| 12  12  12  12  12  12  12  12  76  76  17  17  17  17  17
    497| 12  12  12  12  12  12  12  12  12  17  17  17  17  17  17
    498| 12  12  12  12  12  12  12  12  12  12  17  17  17  17  17
    499| 12  12  12  12  12  12  12  12  12  12  17  17  17  17  17
    500| 12  12  12  12  12  12  12  12  12  12  31  31  31  17  17
    501| 12  12  12  12  12  12  12  12  12  31  31  31  31  31  31
    502| 12  12  12  12  12  12  12  12  12  31  31  31  31  31  31
    503| 12  12  12  12  12  12  12  12  31  31  31  31  31  31  31
    504| 12  12  12  12  12  12  12  12  31  31  31  31  31  31  31
    505| 12  12  12  12  12  12  12  31  31  31  31  31  31  31  31
About PCI Help Gateway