[GRASS-user] modis data

[Benjamin Ducke]

On 06/01/2010 09:10 PM, Hamish wrote:
> bharath s wrote:
>>         iam working on modis data (mydo9q1 250 m) using
>> grass (gis) software.  i   want to overlay google earth
>> boundary for southindia..  after geocorrection on modis data...  
>> but the boundaries are not matching. please help me to solve
>> this problem. is the projecton playing any role in it ?
>> actually iam  using lat/long  and datum as wgs84.
>
> I would try to use the natural earth vector boundary instead of
> Google's one.

Yes, indeed. Since Google's shiny 3D toy is getting dangerously close to being 
accepted into mainstream science and research now, one should be aware that 
there are differences between Google's private way of handling lat/lon 
projections and  international geodetic systems:

http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx

This will lead to inaccuracies when trying to overlay Google data and EPSG 4326 data.
The same problem exists for Microsoft's clone of Google Earth (they do seem to take
the copying business serious at MS). The magnitude of error will vary with your
region's scale and location.

NASA's 3D Earth tool is, as may be expected, more competent, so perhaps the
better choice for 3D GIS visualization:

http://worldwindcentral.com/wiki/Map_projection_Plug-in

Best,

Ben

>
> see 1:10 million, 1:50 million and 1:110million scale maps from
> http://grass.osgeo.org/wiki/Global_datasets#Natural_Earth_imagery
>
> if 1:10m is too crude for you, there NOAA's coastline extractor
> + v.in.mapgen, or v.in.gshhs from wiki addons; or others listed
> on the above wiki page.
>
> see also  http://grass.osgeo.org/wiki/MODIS
>
>
> Hamish
>
>
>
>       
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