I am trying to merge four GeoTiffs from the National Elevation Dataset (EPSG: 4269) into a 2x2 DEM using gdal_merge.py. For some reason, when it merges the upper two NED rasters, gdal produces a seam between the two of approx. 1 px that it fills with incorrect values (either 0 or some large negative number). It seems like this is probably an alignment issue. How can I eliminate this artifact?
Thanks for the help.