Clipped DRG files

DRG files for Washington are being clipped to quad boundaries through a script loosely adapted from the work of Phil Hurvitz. My version of wa24kutm and wa24utm11 are used for clipping. A mask is constructed from the polygonal coverage, and the image is clipped and resaved. The east-west lines on the clipping polygons contain 10 vertices, so they properly reflect the curves of the edges. Overedge quads should go out to the paper edge on that side.

Any DRG files in my collection that do not have an entry in my index map (These are quads that are probably totally outside Washington.) are not represented as clipped DRGs. The small-scale (1:100K and 1:250K) quads are not now clipped.

You gain the ability to mosaic adjacent quads together, while sacrificing tic marks and other information in the map margin.

7.5' quads, as represented in UTM coordinates, are never perfect rectangles. These images are clipped to the smallest rectangle containing the quad.

I have replaced my old clipped images with new rectangles. I merged (in ARC/INFO) large blocks of DRG images, then clipped out the smallest rectangle that contains the 7.5' quad. Except for the edge of the state, no image contains no-data pixels. When they do occur, no-data edges are white instead of black. Overedge quads are not clipped on those edges.

more updates
Note the links to mosaicked one-degree blocks of 1:24K images. The "z" prefix is my own invention. Caution: this are huge files.

GeoTIFF Troubles

The USGS creates these files in GeoTIFF format so that applications will know where they are geographically, even without the tfw file. Some of this can be seen in ASCII:
% unzip -p o48122h5.tif | strings
USGS GeoTIFF DRG 1:24000 Quad of Bertrand Creek. Product:531339
USGS CD Archiver program tif2usgsdrg v.1.0
1997:02:10 13:29:59
UTM Zone 10 N with NAD27
When images and imported to ARC/INFO and then exported, some information is lost:
% unzip -p ../../drgclip/victoria/ o48122h5.tif | strings
There are two more problems with tif files created by ARC/INFO (ARC/INFO workstation 8.1.2). First, there is a rounding error in some tfw files, such that the cell size may be 2.43839999999998 or 2.43840000000002 instead of 2.43840000000000. This can prevent some software from mosaicking images. This problem has been eliminated on thenew rectangular files. Secondly, these tif files are unreadable to ENVI software. They can be made readable to ENVI if they are brought into and out of photoshop, though this wipes out all the internal GeoTIFF information. Anybody have any thoughts on this?

Harvey Greenberg