gdal_contour weirdness anyone?

[cbellevie]

I've been using topo_process to create my contours and have found along the coast of WA and in large bodies of water I have a number of weird lines which are not produced when using DEM2TOPO.

Anyone know what the weirdness is in the attached image and what I might be doing wrong?

Thanks for any help!

Chris

[-Oz-]

umm, wow.

I had some issues with hawaii where it would draw one line at the edge of each quad; but this is very very different.

[maps4gps]

I also get those with Global Mapper.  It appears USGS's process to 'edge match' data from individual 7 1/2' quads does not work very well at times.  Also that a mask for sea level (nor large lakes/reservoirs) was not used, so the DEM can have numerous areas slightly above and below the water level which then get contoured.  There are also bad situations were they patched in data at a different resolution along the US-Canada border in the eastern portion of the US.

[cbellevie]

Thanks for the feedback!

All the lines/patterns are 0 elevation and it seems the best solution I can come up with that avoids processing all the data again with DEM2TOPO (which has the 'sea level threshold' option) is to remove all lines with 0 elevation. Hopefully this can be done with GPSMapEdit... looks easy with GlobalMapper.