The panel contains several subareas. At the top is the menubar containing the GCP loading and saving options (``File'' pulldown), the GCP Scatterplot, Image Fit and Coefficient Reports (``Reports'' pulldown), and options for controlling elevation data (``Elevation'' pulldown).
Following this is the GCP Editing area. It shows the currently edited GCP point values, and the Accept as GCP, Use as Check Pt, and Delete action buttons. The GCP values are all editable, and include the GCP Id, the point in the georeferenced image in georeferenced coordinates, the point in the uncorrected image in pixel/line coordinates, and the elevation of the point if elevation has been activated on the Elevation pulldown.
The Accept as GCP, Use as Check Pt, and Delete action buttons determine what is done with the currently edited GCP point. The Accept button will move the GCP point down into the Accepted GCP list, the Use as Check button will move the point down into the Check GCP list, and the Delete button will remove the point. After an action button is used, a new blank GCP with a unique Id will be generated and placed in the GCP Editing area.
The Model subarea allows the user to select the order of the polynomial used to fit the uncorrected points to the georeferenced points. Models with orders higher than 1st are only available when enough GCPs have been collected to support the order.
The RMS Error is the root mean square error generated from the reported GCP residual errors. If there are more GCPs than terms in the Model order, an RMS adjusted for the number of terms is reported. If there are as many or fewer GCPs as terms for the Model order, the RMS error is N/A (or Not Applicable). For example, an RMS error is reported for a 1st Order model when more than 3 GCPs are collected.
The Accepted GCPs subarea contains a list of all the GCPs currently used in the computation of the registration model. They may be ordered according to the Id number, or the size of the residual error depending on the setting of the ``GCP Ordering'' radio buttons. There are four values shown for each GCP:
Id: Error ( Residual X,Y )The Check GCPs subarea is similar to the Accepted GCPs subarea; it is a list of GCPs that have been collected, but are not included in the computation of the registration model.
In order to move GCPs from one list to another, or to edit or delete an existing point, it is possible to select a new current GCP point from the Accepted or Check GCP lists.
See Also: {WORKS|Data File|Read GCP Text File}
{WORKS|Data File|Write GCP Text File}
GCPs are saved to an existing or new PCIDSK auxiliary segment. If the georeference system defined for collecting GCPs is not a simple projection and the GCP georeference system can be projected and the "Mathematical Model" selected for the "GCPWorks Setup" panel is not "Satellite Ortho Correction", the GCPs will be reprojected to equivalent LONG/LAT values before they are saved. (See the LONG/LAT subtopic for more details.)
If more GCPs were to be added in a future GCPWorks session, the georeference system for collecting the GCPs should be set up before loading the existing GCPs. Then the LONG/LAT GCPs would be reprojected to that georeference system when they are read in.
The ``Save HI-VIEW Ground GCPs'' entry can be used to save the geocoded GCPs to a file named ground.dat in HI-VIEW format. The ``Save HI-VIEW Mono GCPs'' menu selection can be used to save the uncorrected GCP coordinates to a file named photo.dat.
The ``Save HI-VIEW Stereo GCPs'' entry can be used to save the current uncorrected and master GCPs in a HI-VIEW format photo.dat file. This option should only be used in Image To Image tiedown if both images are in pixel/line coordinates.
"LONG/LAT" coordinates.2. Convert the equivalent "LONG/LAT" GCPs to the output "TM" system
with GCPPRO.3. Use the "TM" GCPs produced from GCPPRO as input to REG.
Write Permission
The following message is produced when the selected database file to
which the GCPs are to be saved cannot be opened with write access.
Typically this is a UNIX permissions problem that must be rectified
outside of GCPWorks.
``Unable to open database `xyz' with write permission.''
Non-PCIDSK File
Currently, GCPs can only be stored in PCIDSK file auxiliary
segments. Any attempt to save them to another database file type
will result in the message:
``Unable to save GCPs to a non-PCIDSK file.''
Corrected GCP Georeferencing Illegal
The georeferencing system of the corrected GCPs must either be
PIXEL or match the georeferencing of the selected geocoded database
or geocoded area. The following message will be generated:
``Unable to use geocoded GCPs with a georeferencing system of:%s''
Uncorrected GCP Georeferencing Illegal
The georeferencing system of the uncorrected GCPs must be PIXEL. If
it is not the following message will be generated:
``Unable to use uncorrected GCPs with a georeferencing system of:%s''
GCPs are loaded from an existing or new PCIDSK auxiliary segment. The GCPs currently in memory are replaced by the newly loaded GCPs.
If the existing GCPs are in different georeference units than the georeference system defined for collecting GCPs and they can be projected, the GCPs will be reprojected to the georeference system that is defined for collecting the GCPs.
This report will be updated each time the GCP list is changed. It may be popped down by selecting the `Close' entry from the window frame pulldown menu.
The Image Fit Report shows a graphical representation of the outline of the georeferenced image area, uncorrected image area, mosaic cut line, and GCP points. The uncorrected image outline is transformed according to the current GCP model.
This report will be updated each time the GCP list is changed. It may be popped down by selecting the `Close' entry from the window frame pulldown menu.
The Model Coefficients report is simply a textual display of the forwards and backwards transformation equations currently being used. This report will be updated each time the model is updated.
The coefficients are for equations relating pixel/line coordinates on the master image and pixel/line coordinates on the raw image. In cases where there is no master image (tiedown to vectors, map, etc) the equation will relate georeferenced coordinates to raw image coordinates.
The elevation values must be user entered in the ``Elev'' editable field of the ``GCP Selection and Editing'' panel, and will be saved or loaded with the GCP points.
To enable the elevation option, select ``Enable Elevation'' from the ``Elevation'' pulldown menu of the GCP panel. By default, the elevation is interpreted in metres. This can be changed to feet by selecting ``Elevation in FEET'' from the ``Elevation'' menu.