[Gdal-dev] convert HDF ASTER to geotiff

[vincent at ecovla.nl]

Jon Saints wrote:

> Ok, I have narrowed the problem.
>
> Yes, I agree that ASTER's come with ground control points, however,
> when using gdal_translate it seems that the utility doesnt apply the
> ground points correctly.
>
> My observation is this: In the raw aster image the corners (ul and
> lr) of the raw image data are not the "corners" of the data. Along
> both edges of the actual data there are no data values hold space as
> padding. The actual image data is a slanted trazezoid padded on both
> sides with no data values within the rectangle that is the raw aster
> image. gdal_translate can apply the GCP points to the raw image, but
> does so incorrectly. It applies the ul and lr values to the no data
> padding of the raw image, rather than applying the point to the
> actual corner where the actual data begins.
>
> I hope this makes some sense. I found it difficult to explain without
> drawing pictures.
>
> Is there any workaround for this?
>
> Thanks Jon


Jon,

Are you sure that for your ASTER images, the GCP's don't apply to the
nodata areas too? In the ASTER images that I have used so far, the
opposite is true. GCP's range from (0.5, 0.5) to the full pixel extent
of the ASTER image (that is: including the nodata areas) , i.e. the last
GCP maps pixel coordinate (2490.5,2100.5). This of course would never be
so if the nodata parts were not covered by the GCP's. Moreover, the
georeferencing that I've done using gdalwarp (note: NOT gdal_translate)
looks very accurate; I'm sure I would have noticed it all my ASTER
images were rotated and slanted.

You can check the values of the GCP's using gdalinfo on one of the
subdatasets of your ASTER HDF files.

just my 2c.

regards,
Vincent.

>
>
> --- Kenneth Melero <kmelero at sanz.com> wrote:
>
>> Andrey,
>>
>> Can you provide an example of this?
>>
>> Thanks! -Ken
>>
>> -----Original Message----- From: gdal-dev-bounces at xserve.flids.com
>> [mailto:gdal-dev-bounces at xserve.flids.com] On Behalf Of Andrey
>> Kiselev Sent: Saturday, April 30, 2005 2:42 AM To:
>> gdal-dev at remotesensing.org Subject: Re: [Gdal-dev] convert HDF
>> ASTER to geotiff
>>
>>
>> On Fri, Apr 29, 2005 at 01:18:15PM -0700, Jon Saints wrote:
>>
>>> Hi, I am new to GDAL. I have had some success
>>
>> converting hdf to tif
>>
>>> using gdal_translate.
>>>
>>> i have not been able to apply a coorsys to the new
>>
>> tif image. has
>>
>>> anyone any expirience with this sort of thing?
>>
>> ASTER scenes are georeferenced with GCP points, that means you
>> should use gdalwarp to transform the scene in desirable projection
>> and extent. And you definitely need the latest CVS snapshot of GDAL
>> sources where the proper functionality has been implemented.
>>
>> Regards, Andrey
>>
>> -- Andrey V. Kiselev Home phone: +7 812 5970603 ICQ# 26871517
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