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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>> Is there a way to access the Latitude and Longitude
data with gdal or do I have to drop down to using the HDF4 library directly?<br>
<font color=navy><span style='color:navy'>There is several ways to query and hide
information inside a HDF4 file and unfortunately the data providers know that
;-). So if you are going to write your own code, check out the return of SWinqgeofields,
if returns something other then zero it means that you will not find a “Latitude”
and “Longitude” subdataset to read the geolocation from. Not with
that name “Latitude” and “Longitude” but with the names
that SWinqgeofields ‘returns’ in the second parameter. Good
luck<o:p></o:p></span></font></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
gdal-dev-bounces@lists.maptools.org
[mailto:gdal-dev-bounces@lists.maptools.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Huw Lynch<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, December 19, 2006
7:24 PM<br>
<b><span style='font-weight:bold'>To:</span></b> gdal-dev@lists.maptools.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Gdal-dev] accessing
MODIS L1B geolocation data with gdal</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><br>
Sorry if this question has been asked before; I've searched but can't find a
full explaination.<br>
<br>
I am trying to access geolocation information in MODIS L1B data files. I was
hoping that the Latitude and Longitude data sets would be visible via gdalinfo
however when I run this those 2 datasets appear to be skipped over.<br>
<br>
Here's a gdalinfo output from an example modis data file;<br>
<br>
$ gdalinfo MOD03.Terra20061216T021152Z20061216T021611Z.hdf <br>
Driver: HDF4/Hierarchical Data Format Release 4<br>
Size is 512, 512<br>
Coordinate System is `'<br>
Metadata:<br>
--cut--<br>
ASSOCIATEDSENSORSHORTNAME=MODIS<br>
ASSOCIATEDPLATFORMSHORTNAME=Terra<br>
ASSOCIATEDINSTRUMENTSHORTNAME=MODIS<br>
--cut--<br>
PROCESSVERSION=5.0.2<br>
--cut--<br>
Subdatasets:<br>
SUBDATASET_1_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:Height<br>
SUBDATASET_1_DESC=[1620x1354] Height (16-bit integer)<br>
SUBDATASET_2_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:SensorZenith<br>
SUBDATASET_2_DESC=[1620x1354] SensorZenith (16-bit integer)<br>
SUBDATASET_3_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:SensorAzimuth<br>
SUBDATASET_3_DESC=[1620x1354] SensorAzimuth (16-bit integer)<br>
SUBDATASET_4_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:Range<br>
SUBDATASET_4_DESC=[1620x1354] Range (16-bit unsigned integer)<br>
SUBDATASET_5_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:SolarZenith<br>
SUBDATASET_5_DESC=[1620x1354] SolarZenith (16-bit integer)<br>
SUBDATASET_6_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:SolarAzimuth<br>
SUBDATASET_6_DESC=[1620x1354] SolarAzimuth (16-bit integer)<br>
SUBDATASET_7_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:Land/SeaMask<br>
SUBDATASET_7_DESC=[1620x1354] Land/SeaMask (8-bit unsigned integer)<br>
SUBDATASET_8_NAME=HDF4_EOS:EOS_SWATH:"MOD03.Terra20061216T021152Z20061216T021611Z.hdf":MODIS_Swath_Type_GEO:gflags<br>
SUBDATASET_8_DESC=[1620x1354] gflags (8-bit unsigned integer)<br>
<br>
I'm certain that the Latitude and Longitude data is there, because I can see it
with hdp;<br>
<br>
$ hdp dumpsds -h MOD03.Terra20061216T021152Z20061216T021611Z.hdf<br>
--cut--<br>
Variable Name = Latitude<br>
Index = 0<br>
Type= 32-bit floating point<br>
Ref. = 20<br>
Rank = 2<br>
Number of attributes = 3<br>
Dim0:
Name=nscans*10:MODIS_Swath_Type_GEO<br>
Size = 1620<br>
Scale Type = number-type not set<br>
Number of attributes = 0<br>
Dim1:
Name=mframes:MODIS_Swath_Type_GEO<br>
Size = 1354<br>
Scale Type = number-type not set<br>
Number of attributes = 0<br>
Attr0: Name = units<br>
Type = 8-bit signed char <br>
Count= 7<br>
Value = degrees<br>
<br>
Is there a way to access the Latitude and Longitude data with gdal or do I have
to drop down to using the HDF4 library directly?<br>
<br>
The frmt_hdf4.html file shipped with gdal includes an example as such;<o:p></o:p></span></font></p>
<pre><font size=2 face="Courier New"><span style='font-size:10.0pt'>$ gdalinfo GSUB1.A2001124.0855.003.200219309451.hdf<br>
Driver:<o:p></o:p></span></font></pre><pre><font size=2 face="Courier New"><span
style='font-size:10.0pt'> HDF4/Hierarchical Data Format Release 4<br>
Size is 512, 512<br>
Coordinate System is `'<br>
Metadata:<br>
HDFEOSVersion=HDFEOS_V2.7<br>
Number of Scans=204<br>
Number of Day mode scans=204<br>
Number of Night mode scans=0<br>
Incomplete Scans=0<o:p></o:p></span></font></pre>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>...a lot of metadata output skipped...<o:p></o:p></span></font></p>
<pre><font size=2 face="Courier New"><span style='font-size:10.0pt'>Subdatasets:<br>
SUBDATASET_1_NAME=HDF4_SDS:MODIS_L1B:GSUB1.A2001124.0855.003.200219309451.hdf:0<br>
SUBDATASET_1_DESC=[408x271] Latitude (32-bit floating-point)<br>
SUBDATASET_2_NAME=HDF4_SDS:MODIS_L1B:GSUB1.A2001124.0855.003.200219309451.hdf:1<br>
SUBDATASET_2_DESC=[408x271] Longitude (32-bit floating-point)<br>
SUBDATASET_3_NAME=HDF4_SDS:MODIS_L1B:GSUB1.A2001124.0855.003.200219309451.hdf:2<br>
SUBDATASET_3_DESC=[12x2040x1354] EV_1KM_RefSB (16-bit unsigned integer)<o:p></o:p></span></font></pre>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'><br>
Even if it's not possible to get at the lat/lon data with gdal, I'm interested
in understanding why it doesn't work.<br>
<br>
Cheers & thanks<br>
<br>
Huw Lynch<o:p></o:p></span></font></p>
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