Re: Problem solved with the lakes

Hi Stacie,

> This might be more of a problem since I am using SRTM 1 arcsec terrain
> instead of the 30 arcsec data.  Also, with using the higher res data
> for terrain it seems that the accuracy of the VMAP0 database might
> become a problem.

VMAP0 is 1:1 million scale (ie quite crude), and uses the NAD83 map
datum on a GRS80 ellipsoid.

SRTM-1 is 30m resolution, and uses the WGS84 map datum in the horizontal
and the EGS96 datum in the vertical. (difference between WGS84 geoid and
EGS96 is mostly minor; just ignore)


I think for U.S. coverage (ie where SRTM-1 exists) it might be better
for you to use TIGER data (US Census) instead of VMAP0. Use the ogr2ogr
program from GDAL/OGR to reproject into WGS84 and convert to the data
format you need. (VMAP0 is supported by the OGDI driver)
see  http://www.gdal.org/ogr/

probably need PROJ.4 as well for any reprojections and datum transforms:
 http://www.remotesensing.org/proj

(GDAL & PROJ4 are maintained together)

I know of an article to be published soon on SRTM+VMAP0 written by a
colleague, can post a link to it here once it is in press if anyone is
interested.


regards,
Hamish

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