A chip database is a compilation of individual image samples, called chips, usually measuring 256 pixels by 256 pixels or smaller. Each image section contains an accurate geocoded location and metadata, such as which sensor it was generated from, the date it was acquired, the viewing angle, and so on. These chips, can be used to collect ground control points (GCPs). You can visually match a feature in the raw image that you are georeferencing and use the coordinates from the chip database as a GCP or use the chips to automate the collection of GCPs.
With the Chip Manager, you can create new chip databases, add or remove chips from existing chip databases, and merge different chip databases. You can use the chips to collect ground control points (GCPs) on the raw images in your project. Having a chip database eliminates the need to repeatedly collect the same GCPs on imagery of the same area in a project.
This tutorial outlines the steps required to import GPS points in a text file into a 3D point layer in Geomatica and then use this point layer along with a georeferenced image to create an image chip database in the PNT2CHIP algorithm.
Import ASCII GPS points to a 3D PIX point layer (Focus)
Before the GPS points can be used in a chip database they must first be imported into a 3D PIX point layer. Your original ASCII file should have 3 columns: X, Y, Z. For example the txt file being used in this tutorial, l7_fuse_ascii_gcp.txt, has the following information in three columns:
452392.222222 3741977.777778 278
453529.349794 3735893.958848 404
463245.000000 3739052.777778 624
461681.111111 3742636.111111 440
462917.222222 3745477.777778 472
462183.888889 3747694.444444 430
459620.000000 3748322.222222 362
458700.555556 3746252.777778 386
454745.000000 3746275.000000 397
449470.000000 3748994.444444 189
To import this file into a PIX file you can use the Import ASCII Table/Points utility.
1. Open Focus from the Geomatica 2015 toolbar
2. In Focus navigate to File > Utility > Import ASCII Table/Points
3. Browse to the required .txt file that contains the ASCII GPS points.
4. Once the fields have been filled with the text file information click next.
5. On the next screen the columns from the text file will be separated into different fields.
6. On the third step you will need to change the Data Type of all three fields to double.
7. In the Coordinate Fields section select Field_1 for X, Filed_2 for Y and Field_3 for Z. Once this is completed the Projection section will become available. Choose the correct projection information.
8. Click Finish
This will create a 3D point layer (X,Y,Z) rather than a 2D Point layer (X,Y) with the elevation stored in an attribute. PNT2CHIP requires a 3D point layer if you are not extracting the elevation values from a DEM. You cannot use a 2D point layer with the elevation value in an attribute in PNT2CHIP.
Import ASCII GPS points to a 3D PIX point layer (EASI)
You can also import the GPS ASCII text points into a PIX vector segment in EASI using the Generic ASCII Vector (GAV) format in FIMPORT. In the example above, you would use l7_fuse_ascii_gcp.txt as FILI in FIMPORT. You need to create an associated schema file l7_fuse_ascii_gcp.gav with the same filename prefix in the same directory as the *.txt file. This file defines the attributes of the txt file. When you run FIMPORT this gav file will automatically be found by FIMPORT. For more information on the Generic ASCII Vector format, refer to the general help in Focus Contents tab, +Technical Reference, +GDB File Formats, +Supported File Formats, +Working with Generic ASCII Vectors (GAV).
Before running FIMPORT in EASI you will need to create the gav file.
1. Open notepad and enter the following information:
NAME: SIMPLE XYZ - Variable
MAPUNITS: "UTM 11 S E000"
DATA: TYPE(X) POSITION(1)
DATA: TYPE(Y) POSITION(2)
DATA: TYPE(Z) POSITION(3)
2. Make sure that your gav file has the same name as your txt file and saved it in the same location (ex. l7_fuse_ascii_gcp.gav).
3. Open EASI from the Geomatica 2015 toolbar.
4. In this window you will need to run FIMPORT. First type s fimport. This will display the parameters in the algorithm.
5. The FILI and FILO parameters will need to be changed based on your data. Once these values are set you can run FIMPORT by typing r fimport.
Using PNT2CHIP to convert from points to a chip database
Once the point pix file has been created using one of the methods outlined above, this point layer can be used with a georeferenced image to create a chip database. The following example uses EASI but Modeler or Python could be used instead.
1. In EASI type s pnt2chip. The parameters for pnt2chip are displayed. Since there are various parameters that need to be defined you can create an .eas file to define the parameters.
2. Open a new notepad file. Enter all of the parameters and the run functions as follows. Keep in mind that the actual parameter values may be different for your data. You can find more information about the parameters by searching pnt2chip in the general help.
geofile = "Y:\Tutorial\CHIP\l7_fuse.pix"
dbic = 1
backval = 0
filv = "Y:\Tutorial\CHIP\3D_Points_2015EASI.pix"
dbvs = 2
chipfile = "Y:\Tutorial\CHIP\l7_fuse_chip.cdb"
chipsens = "Landsat7"
chipdate = "16nov1999"
chipsize = 256
3. You will need to save this notepad file as a .eas file in the following directory: C:\PCI Geomatics\Geomatica 2015\pro . In this example the file was saved as pntchip.eas.
4. Once your eas file is saved in the pro directory switch back to the EASI window. In the window type r and then your filename. For example, r pntchip.
5. If there is an issue with your eas file EASI will tell you where the problem is.
6. You can open your new cdb file in the Chip Manager window. On the Geomatica toolbar click Chip Manager. From the file menu click open and choose your cdb file.