PPTABLE

Description

Parameters

Parameter descriptions

FILE

Specifies the name of the PCIDSK image file to process.

FDEP

Specifies the input channel that contains the filled depression data.

DBIC

Specifies the input channel that contains the watershed results. This channel is obtained by running the WTRSHED function. The input channel must be 16-bit signed integer or 32-bit real.

DBIW

Specifies the raster window (Xoffset, Yoffset, Xsize, Ysize) that is read from the input image. If this parameter is not specified, the entire image is processed by default.

Xoffset, Yoffset define the upper-left starting pixel coordinates of the window. Xsize is the number of pixels that define the window width. Ysize is the number of lines that define the window height.

REPORT

Specifies where to direct the generated report.

Available options are:

• TERM: generates a report on the terminal (default)
• DISK: generates a report on file "IMPRPT.LST"
• OFF: turns off report generation
• <filename>: appends a report to the specified file

Details

PPTABLE finds all the pour points between watersheds (a table of linkages for watersheds) and stores them in a table. Pour points are the points of lowest elevation on the common boundary in between watersheds.

To use OVERLND, you must first run the DWCON function.

For more information about the drainage network functions, see the help for DWCON.

PPTABLE prints out, in tabular form, the pour points of all watersheds. A watershed links to another at a pour point, the point of lowest elevation on the common boundary between the two watersheds. If a watershed were to be filled with water, this minimum elevation is where the water would "pour" into its neighbor. To accommodate data sets with internal (or closed) drainage, or where two or more pour points leading to different watersheds are very close or equal in elevation, all possible pour points are computed. PPTABLE uses the filled depression channel and the watershed results to produce a pour point table. For each watershed, all bordering watersheds are examined, including the watersheds with a label of zero indicating that they flow to the data set edge, and a pour point is found on each watershed-to-watershed border. The line and pixel coordinates and elevation of each pour point are recorded in the table.

Areas that are not well drained will exhibit multiple pour points of the same elevation, while well-drained areas will rarely exhibit this feature.

The pour point table results can be transferred to a relational database management system where the linkages can be used to aggregate watersheds. The line and sample coordinates of the pour point can also be transferred to a vector-based spatial analysis system as point data sets for additional analysis and plotting.

FDEP (InputFDEP) specifies the filled depression channel, which is obtained by running the DWCON function.

DBIC (Input DBIC) specifies the channel of that contains the watershed results, which is obtained by running the WTRSHED function.

DBIW specifies the window of image data from the file to analyze.

Example

The following is an example of running PPTABLE.

EASI>file	=	'irvine.pix'	! input file
EASI>fdep	=	11	! input fill depression channel
EASI>dbic	=	16	! input watershed results channel
EASI>dbiw	=		! process entire image
EASI>report	=		

EASI>run PPTABLE

         THIS IS THE COMPLETE LIST OF POUR POINTS
 SEQUENCE NO.   LABEL PAIR     ELEVATION     X    Y  
      1           0 -  10          84        60   79
      2           0 -   5         180       126    2
      3           0 -   1         409       466   11
      4           5 -  10         173       106   26
      5           1 -   2         411       466   12
      6           0 -   2         411       466   12
    ...         ...   ...         ...       ...  ...
    240          79 -  80          81       126  469
    241          80 -  82          81       128  471
    242          81 -  82          81       130  471
    243          79 -  82          88       126  475
    244           0 -  82         105       169  508

References

Jenson, S.K. and Domingue, J.O. "Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis". Photogrammetric Engineering and Remote Sensing, Vol. 54, No. 11, November 1988, pp. 1593-1600.