CDASAR

Description

Parameters

cdasar(fili, filo, cdic, tex1)

Parameter descriptions

FILI

Specifies the full path and file name of the ESA ENVISAT-format file with the .N1 extension.

FILO

Specifies the name of the PCIDSK file to receive the data. This file is created automatically and must not already exist.

CDIC

Specifies the list of channels to read from the CD.

For each channel specified, a channel is created in the PCIDSK file.

If this parameter is not specified, all channels are read.

TEX1

Optionally specifies a line of text that describes the file. Typically, this contains information that identifies the location of the data and the CD reference number.

Return Value

Returns: execution status

Type:  PCI_INT

The return value is 0. This function returns only if it executes successfully; otherwise, it throws an exception.

Details

CDASAR is part of the satellite orthorectification component. It reads the ASAR file format CD when satellite orthorectification is required. CDASAR automatically creates a PCIDSK file, reads the requested imagery channels from the CD, and saves the satellite path information in an ORBIT segment. The output is used in CATALYST Professional OrthoEngine.

The ESA provides access to different ASAR products. CDASAR does not support level 0 products, global monitoring mode products, wave mode products, browse products, or geocoded products. The remaining level 1 products in the image mode, alternating polarization mode, and wide swath mode are supported.

Single-look complex images such as ASA_IMS and ASA_APS do not have the antenna pattern information included within their data product. For these images, CDASAR extracts the nominal antenna pattern from the ASAR external calibration data file ASA_XCA_AX. The time-stamped file must be included with the image in the AX subdirectory, or it can be downloaded from the ESA web site (http://envisat.esa.int/handbooks/asar/CNTR6-5-3.htm).

The FILO parameter specifies the name of the PCIDSK file that holds the image, orbital information, and auxiliary information obtained from the CD. This file is automatically created with the dimensions required to hold all of the requested data. Before running CDASAR, you must ensure that sufficient disk space is available.

CDASAR extracts the geographic coordinates from the CD on the scene center and on the four corner points. These extracted coordinates are stored in the ORBIT segment in the generated image.pix file. If a sufficient number of ground control points (GCPs) is unavailable, the extracted coordinates can be used as GCPs by any other routine, such as SATMODEL, to obtain an approximate sensor model calculation. To obtain an exact calculation, however, a sufficient number of GCPs must be used for each scene or a block of scenes.

CDASAR also extracts GCPs from the geolocation grid ADS, and stores them in the GCP segment. Up to 255 GCPs are extracted. If there are more GCPs in the input image, they are uniformly decimated.

The DBGC (OutputGCP) parameter receives the number of the segment that contains the GCPs.

The ORBIT (OutputOrbit) parameter receives the number of the segment that contains the orbital information. The orbital information in this segment is required for CATALYST Professional OrthoEngine.

Additional information is extracted from the input image and stored in array segments. The information is used in the downstream, SAR-specific SARBETA, SARSIGM and in the optional radiometric terrain correction step in OrthoEngine.

The created segment numbers are stored in the A0SEG, ASCALSEG, INCIDSEG, and SRGRSEG parameters. If two channels of an alternating polarization image are imported, two ASCALSEG segments are created and their numbers are returned to the ASCALSEG parameter. The SRGRSEG parameter is only set if the SRGR segment is created for the input images with more than one record in the SRGR ADS.

If the parameters required for the ORBIT segment do not exist in the input image or cannot be retrieved, CDASAR issues an error message and aborts without generating the PCIDSK file. If the parameters required for the SAR-specific process do not exist in the input image or cannot be retrieved, the generated image is created without the SAR-specific array segments.

Example

Read in an ASAR file and create a PCIDSK file from it.

from pci.cdasar import cdasar

fili	=	"ASA_IMP_1PNDPA20021103_055409_000000162010_00478_03538_0001.N1"
filo	=	"Imported_ASAR.pix"
cdic	=	[1]
tex1	=	""

cdasar( fili, filo, cdic, tex1 )

Acknowledgements

PCI Geomatics wishes to acknowledge the assistance of Dr. Thierry Toutin for this software.

References

Toutin, Th. "Analyse mathématique des possibilités cartographiques du système SPOT". Thèse de Docteur-Ingénieur en Sciences Géodésiques, ENSG, Paris, France, 1985: 1-163.

Toutin, Th. and Carbonneau Y. "La multi-stéréoscopie pour les corrections d'images SPOT-HRV", Canadian Journal of Remote Sensing, p110, Vol. 15, No. 2 (September 1989): 110. (Also available in English from the Canada Centre for Remote Sensing.)