NASA提供的中国区域TM影像下载

中国区域TM影像下载

A guide to finding your place in the GeoCover data set.

NASA已经将中国地区的卫星图像发表在其网站上，免费供公众下载，请阅读本文方便您的下载。

仅作学习研究使用，不能商业用途！
The GeoCover data,while presenting imagery of the Earth's surface, does notindicate where something, or some place, is located.

There are several solutions to this problem.

First, if you need to find the latitude and longitude of a place of interest,consult a gazetteer. A gazetteer is a geographical index listing names andlocations, usually listing the locations as latitudes and longitudes. �There are two sources of suchgazetteers on the Internet. �

For places in the United States andAntarctica, the source is the United States Geological Survey (USGS) at URL:

http://geonames.usgs.gov/index.html

This gazetteer is available forquery on the web, or you may download the data via FTP (via the "downloaddata" link) and use them later. �If you are downloading files for future use, download eitherthe ones with the "XX_deci" ending (where XX is the 2-letterabbeviation for the state), or download the "yyyy" files, where yyyyis the state name. �Bothtypes of files are text files (*.txt files) and either type should work.

For other areas of the world, go to the National Imagery and Mapping Agency's(NIMA's) web site at:

http://164.214.2.59/gns/html/index.html

NIMA uses 2-letter abbreviations forcountry files (the abbreviations are standard, and their documentation is onthe NIMA web site.).

The NIMA web site will also give you the choice of entering a query on the website or downloading a database via FTP (unzip them after you download them).

Having found the latitude and longitude of the place you are searching for, youmay go to the US Digital LandsatMosaic viewer included with the U.S. GeoCoverdata set and load the tile you need (it is assumed that you can determine whichtile you need). �Movethe cursor until the readout in the lower left-hand corner is the longitude andlatitude you desire. Then click on the mouse button to zoom in on the locationsought.

If you are using a viewer that does not present the latitude and longitude, butrather presents the coordinates in the Universal Transverse Mercator projection(UTM) described in the Introductory Landsat Tutorial, you must includeanother step. �Youmust transform the latitude-longitude into UTM coordinates of zone, easting,and northing.�Manylatitude-longitude to/from UTM converters are available on the web. �One called llutm is incapsulated in"llutm.zip" and�can be found at: �

ftp://ftp.blm.gov/pub/gis

Unzip llutm.zip and

run the executable �llutm.exe (it will run in a DOSwindow)

An alternative approach is to usethe Excel spreadsheet called "ll_utm.xls" attributed to the SicilianRhyolite Society at Sul Ross State University (included in this directory).

After converting your location intoUTM coordinates (zone, easting, and northing),� load the appropriate tile into your viewer (e.g., the MrSIDGeoViewer from Lizardtech), set the cursor to the appropriate UTM coordinates,and zoom in. �Notethat most viewers list only the eastings and northings, but not necessarily thezone. The name of each GeoCover data tile indicates the zone. �Some examples are:

N-30-50: �Zone 30, northern hemisphere, 50-55degrees North Latitude (England)

S-56-30: � Zone 56, southern hemisphere, 30-35degrees South Latitude (Australia)� �

Another way to find your place is by searching on the place name.

It involves adding a gazetteer tothe GeoCover imagery as an overlay. �Free software that does this is available from the USGS asdlgv32Pro. �Unfortunately,it is only available for PC-type computers running Windows. �Download it from:�

http://mcmcweb.er.usgs.gov/drc/dlgv32pro/

After installing it on yourcomputer, start it, and then open a GeoCover tile using:

�"File"> "Open as new"

Note that when you load a GeoCovertile that is not in the USA set (you can find and download them fromhttp://zulu.ssc.nasa.gov/mrsid), you may have to identify the UTM Zone for thetile (on the drop down Zone menu, scroll to the appropriate zone and click onit) and identify the datum to use (on the drop down Datum menu, scroll down toand click on "WGS84"). The default Zone is UTM zone 15, northernhemisphere, and the default datum is NAD83. �You need to change both. Leave the "Projection" on"UTM" and the "Planar Units"on "Meters".Otherwise, dlgv32Pro is lost and the GeoCover image and the correspondinggazetteer may not overlay one above the other.

Note: You can display either UTMcoordinates, latitude-longitude(geographical) coordinates, or no coordinates atall on the image using:

�"Tools" >"Configure...",

�then click on the "General" tab, and

�check the button you want in the "Grid Display" box near the bottom.

You can re-center the image and zoomin or out by clicking on the rightmost magnifying glass on the toolbar - theone with the "+" outside the circle. A left click zooms into the areaindicated by the cursor, while a right click zooms away.

Now that you have the GeoCover datain the dlgv32Pro window, you need to add a gazetteer file. �

To add a USGS gazetteer file:

You must first download the file(s)for the state(s) you want from the above web site and unzip it(them) into adirectory on your hard drive. �Either of the two forms will work - XX_deci.txt, where XX isthe two-letter abbreviation for the state, or state-name.txt.

Click "File" (upper lefthand corner of your screen), then

"Open into current..."(NOT "Open as new"), and then�

�identifythe gazetteer file to load

Another box will appear asking whichformat. �Doubleclick on "GNIS" for the USGS state files.

To add a NIMA gazetteer file:

Add the NIMA gazetteer file the same way you did the USGS gazetteer file - use:

"File" > "Openinto current..", etc.

You probably will NOT be asked whichformat to use.

In either case (foreign ordomestic), dlgv32Pro will then load the gazetteer and superimpose the pointsand icons on top of the GeoCover image. The area covered by the gazetteer willprobably be blackened with information. �

To find the location you want,

Click on the "Search"button on the tool bar and

Enter the name of the place you wantto go to.

A window will appear with matches -there may be many. �Forexample:

Someplace
Someplace Airport
Someplace General Hospital
Someplace Park

Double click on the name you want.

The image will move and center overthat location.

To zoom into that location withoutmoving the image and loosing your place:

Click on the magnifying glass withthe red cross (or plus sign) in the circle (it's the leftmost magnifying glasson the toolbox).

Keep clicking until you zoom in farenough that the labels spread out and you can see the GeoCover data underneath.

If you want to back away withoutmoving the image, click on the magnifying glass with the red minus sign.

Note: �You can hide the gazetteer names and icons by dropping downthe "control center" �(third button in on the left of the toolbar), highlightingthe gazetteer line, and clicking on "Hide Overlay" button. �You can also bring the gazetterinformation back to the screen using the control center and the "ShowOverlay" button, or delete it from the data sets that you have open viathe "Close Overlay" button.

Once zoomed in, you can use thesearch function ("Search" button on the toolbar) to move to anotherlocation without backing out.

You can move around the image byclicking on the button between the zoom in/zoom out button and the button withthe ruler on it - the one that looks like a funny-looking cross with arrows. �Move the symbol to where you want tore-center the image, and left-click.

You can have up to a total of 4 data sets (MRSID files and/or gazetteer files -or other files) open at any one time in dlgv32Pro.

Good hunting! �Havefun!

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