![[Raleigh West NW DOQQ]](./doqq_hint.gif) | Using DOQQ and DRG CDs | ![[Raleigh West DRG]](./drg_hint.gif) |
Using DOQQs
- What kind of software do I need to use these maps?
DOQQ images are JPG format which can be viewed by many image editing software packages. To use these images with their geospatial capabilities, a CAD (computer-assisted design), GIS (geographic information system), or RS (remote sensing), software package is necessary. The CDs come with USGS software for viewing these images, however this software is obsolete and may not run under Windows 95. The NCGS may not endorse specific software products.
- Can the DOQQs be tiled on the
screen?
Yes, software utilizing georeferenced data can tile the images. Although the NCGS may not endorse specific software products, ESRI provides a free data viewer for GIS data which can be used to view DOQ data. [Instructions on how to use ArcExplorer and DOQQ data]
- Can other data be overlain on
the DOQQs?
Yes, many CAD, GIS, and RS software have the capability to overlay data. Other raster images can be overlain on the DOQQs, but you will not be able to "see" through one image to the other.
- Where on the CD are the images?
Each CD has a directory named /data. In this directory are many files named with filenames like O3307701.nec or O3307701.neh. The files ending in .XXc are the images and the files ending in .XXh are the image header files.
- Where on the CD is any documentation? Or how do I find out which image I need?
Each CD has a directory named /document. Within the document directory is a subdirectory named doqtext. This subdirectory contains text files which describe the contents and production of the CD. The file which explains which image is which quarter quadrangle is doqlist.txt. The file which explains the the organization of the image header files is doqsti.txt
- Are there any differences in CDs I purchase?
Yes, the USGS has changed the format of the image header files. Here is some information on the differences.
Using DRGs
- What is included on a typical CD?
There are three (3) kinds of information: (1) 7.5-minute (1:24,000-scale) topographic maps, (2) 30x60-minute maps (topographic or planimetric), and (3) 1:250,000-scale (1x2 degree) planimetric maps. Resolution is approximately 2.5 meters for 7.5-minute topographic maps. Images are in TIFF raster format. The images are georeferenced to Universal Transverse Mercator (UTM) coordinates. Typical file size is 10 MB.
- What kind of software do I need to use these maps?
DRG images are TIFF format (PackBits compressed) which can be viewed by many image editing software packages.(One that will not work with DRGs is Imaging for Windows95 or Windows NT). To use these images with their geospatial capabilities, a CAD (computer-assisted design), GIS (geographic information system), or RS (remote sensing), software package is necessary. The CDs come with USGS software for viewing these images, however this software is obsolete and may not run under Windows 95. The NCGS may not endorse specific software products, however ESRI produces a free GIS dataviewer called ArcExplorer which may be downloaded from their site. DRG data can be viewed using ArcExplorer (DOQQ data cannot).
- Can the DRGs be tiled on the screen?
Yes, software utilizing georeferenced data can tile the images. Remember that these are image of the topographic maps which include the map collar (the white margin) and that these collars will overlap the adjoining quadrangle.
- Can other data be overlain on the DRGs?
Yes, many CAD, GIS, and RS software have the capability to overlay data. Other raster images can be overlain on the DRGs, but you will not be able to "see" through one image to the other.
- Can different layers be turned on or off?
These images are one layer which can not be separated into separate layers without editing the image itself or using it as a base for digitizing.
- Where on the CD are the images?
Each CD has a directory named /data. In this directory are many files named with filenames like C33077a8.tif. The files beginning with "C" are the 1:250,000-scale quadrangles, with "F" are the 1:100,000-scale quadrangles, and with "O" are the 1:24,000-scale quadrangles. The corresponding file which ends with .tfw are "world files" which help some software packages (like GIS packages) georegister the image.
- Where on the CD is any documentation? Or how do I find out which image I need?
Each CD has a directory named /document. This directory contains text files which describe the contents and production of the CD. The file which explains which image is which quadrangle is drg_list.txt. Some CDs (see map) are produced by the Tennessee Valley Authority (TVA). On these CDs, the file which list DRG image names and quadrangle names is in the /index directory. Even though the file extension is .ndx, this is a text file and can be viewed in any text editor.
