[gdal-dev] Re: How to get the ENVISAT N1 Main Processing parameters

[Knut-Frode Dagestad]

Hi RSyaoxin and Antonio,

I share your interest in these metadata. In addition to the MPH and SPH 
metadata in ASCII-format, Envisat files contain a lot of metadata in 
binary form, e.g. for ASAR:
http://envisat.esa.int/handbooks/asar/CNTR6-6.htm#eph.asar.asardf.asarrec

It would probably be too much to ask for the GDAL Envisat driver to 
import all of this. However, there are some missing metadata which are 
of special importance:

- the calibration factors, which RSyaoxin mentions
- the incidence angles: 
http://envisat.esa.int/handbooks/asar/CNTR6-6-9.htm#eph.asar.asardf.asarrec.ASAR_Geo_Grid_ADSR

Both of this is necessary to be able to calibrate the data, and hence to 
be able to make any geophysical calculations from them.
It would be really nice if the GDAL Envisat driver could be updated to 
read this as well, and most users would not need to rely on (or create) 
external software.

The incidence angles are stored in a small grid at the same size as the 
GCP´s, (order of 100 elements), which does not fit very nicely into the 
GDAL datamodel - it would probably have to be stored as a list of 
metadata strings.

Best regards from Knut-Frode



On 15/05/2011 18:18, Antonio Valentino wrote:
> Hi RSyaoxin,
>
> Il 15/05/2011 14:46, RSyaoxin ha scritto:
>> Hi,I want to calibration the ENVISAT ASAR DATA(.N1 Format). I need to get
>> it's main processing parameters,such as
>> calibration_factors[0].ext_cal_fact[0],first_line_tie_point_angles[0-10],and
>> I wrote: CString
>> sDomain=m_pDataset->GetMetadataItem("MAIN_PROCESSING_PARAMS_ADS_CALIBRATION_FACTORS[0].EXT_CAL_FACT[0]");but
>> I can't get result.
>> However, "CString sDomain=m_pDataset->GetMetadataItem("SPH_FIRST_MID_LAT")"
>> is right.That's Why?How should I go to get necessary information?
>> I turn to Anybody who once did this job for some advice. Thank you!
>> Kind regards.
>>
>
> It seems that the envisat driver do not extracts all metadata from all
> ENVISAT records.
> It just exposes MPH, SPH and GCPs
>
> http://www.gdal.org/frmt_various.html#Envisat
>
>> From my point of view it would be very useful to be able to have access
> to a richer set of metadata from GDAL (at east for SAR products).
>
> If you are only interested in ENVISAT then you could give a try to
>
> https://github.com/bcdev/epr-api
>
> that give you full access to the ENVISAT products eve if, IMHO, it is
> not so handly as GDAL for imagery IO.
>
> Maybe you can use them both: EPR for metadata and GDAL for imagery.
>
> best regards
>