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Archive for the 'topographic maps' Category Page 3 of 6



Goofing Around With Pan-sharpening

Orbiting satellites often have two types of digital imaging sensors:

– Multispectral, i.e. different sensors for different colors (including IR), or different filters in front of the same sensor. Each individual band can be shown as a black-and-white image; multiple bands can each be assigned a color, and combined to form an RGB color image.

– Panchromatic, “meaning all the colors”, a single broad-spectrum sensor. This are usually displayed as a monochromatic image (i.e. black-and-white).

The panchromatic sensors usually have a higher spatial resolution than the multispectral. For example, on the Landsat 7 spacecraft, the 6 multispectral bands have a spatial resolution of roughly 30 meters (a seventh has 60 meters), while the panchromatic sensor has a resolution of about 15 meters. Here’s an example of an image created from three of the Landsat multispectral bands (data from the Global Land Cover Facility):

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Google Earth Index For US Army Map Service Topographic And City Maps

In a previous post on large-format downloadable historical maps, I noted that the Perry-Castaneda Map Library has an interesting digital collection of Army Map Service topographic maps dating from the 1940s and 1950s, covering large areas of Asia and Africa, along with city maps for Japan, China, Korea and Taiwan (Formosa). Over on the Google Earth Community, “PriceCollins” has been creating a KMZ index file for these maps. So far, he has indexed all 435 city maps:

asiacity

And 413 1:250K maps covering most of India, Pakistan and Southeast Asia:

seasiamaps

Each city and rectangle placemark contains a direct download link to the map image at the Perry-Castaneda Library. From the post, it sounds like eventually all the maps will be indexed in this fashion, so it’s worth bookmarking the site and checking it regularly for updates.




Downloadable Large-Format Historical Maps

There are a number of websites that have historic older maps available for online viewing (I’ll list a few of these in an upcoming post), but these sites typically don’t have the maps in high-resolution downloadable formats. You can always zoom in to the highest resolution, do a screen capture, then mosaic the images together if you have the time and patience. But there are a number of websites that do offer downloads of historic (and recent maps) in a high-resolution format. For some maps, a download link will be offered; for others, you’ll have to either right-click on a link to save the map to your computer, or open the image in your browser and then save it to your computer by right-clicking on the image.

Some maps are available in uncommon formats, like MRSid (*.sid), ECW (*.ecw) or JPEG2000 (*.jp2). If your graphics editor can’t open these formats, you can use the TatukGIS Viewer or IrfanView (with the additional plug-ins) to open these files and convert them to a more familiar format like TIF or JPG. Many maps are also available at the highest resolution in PDF format, and you can use a program like PDFCreator to convert them to standard image formats.

Library Of Congress: The US Library Of Congress has an enormous online collection of maps, historic and modern, for the US and the world, searchable and browsable by geographic area, keyword, subject, creator, and title. Most maps are downloadable in the MRSid format in very high resolution, but can also be viewed at various zoom levels online.

The Perry-Castaneda Map Library: Based at the University of Texas in Austin, this site offers modern and historical maps of the entire world at a wide variety of resolutions, mainly in JPG format but some in PDF as well. There’s also a large number of Texas maps (no surprise), and links to additional web map resources. I found the Army Map Service topographical maps of particular interest: 1:250K topo maps of many areas for which topo maps are difficult to find (Africa, Burma, Siberia, and more).

Leen Helmink: Website of a dealer in rare and antique maps, with high-resolution scans of historic maps from around the world, many for sale.

Yale University Map Library: A number of their historical and current maps are available for download in the JPEG2000 format (with more being added all the time).

historic map of Africa

Africa map from Yale collection (resized 10x smaller than the original in pixel dimensions, 100x smaller in pixel area)

University Of Connecticut: Many historic maps, primarily of the New England and Mid-Atlantic region, most both viewable online and downloadable in MRSid format.

The Atlas Of Canada: Modern and historic maps of Canada, many (but not all) downloadable in JPG and PDF formats; check the bottom of the individual map pages to see if there are download links available. PDF maps are usually of higher quality than JPG.

Michigan State University: Primarily maps of Michigan, but some maps of Africa and North America.

Quebec National Library And Archives: In French, but you should be able to get around. Mainly maps of Canada and North America, browsable by titles (“titres”), authors (“autheurs”), by time (“chronologique”) and area (“toponyme”). Look for the link titled “la carte agrandie” to open the map image at full resolution in a new window, then right-click on the image to save it.

W. M. Keck Earth Sciences and Mining Research Information Center: Large selection of historic and modern maps of Nevada and surrounding areas.

Know of a good site that I’ve missed? Post it in the comments, and I’ll do a follow-up post later.




Creating GeoTiffs From TerraServer Imagery With MicroDEM

TerraClient offers a fast and simple way to get TerraServer black-and-white aerial imagery covering large areas, but with no georeferencing data that lets it be used directly in a GIS. USAPhotoMaps offers a convenient and easy interface for downloading TerraServer topo and aerial imagery of smaller areas, with georeferencing data in worldfile format. But the USAPhotoMaps images are saved in JPEG format resulting in some minor image quality degradation, and the worldfile data doesn’t include information like the coordinate system and datum. For that, you’d want to have the TerraServer imagery saved in a format that embeds georeferencing, coordinate system and datum into the actual file format, like GeoTiffs. MicroDEM offers the ability to download TerraServer imagery and then save it in GeoTiff format. While the process and interface are a bit more convoluted than that for USAPhotoMaps or TerraClient, it’s not too bad.

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USAPhotoMaps: GPS Functions

USAPhotoMaps has built-in GPS interface capabilities for Garmin GPS units; it also supports the general NMEA GPS interface for other units. While there are a lot of GPS functions, they’re a mixed bag. Waypoint creation, export, and import on the fly are pretty easy (with some minor quirks), and USAPhotoMaps is my program of choice for quickly creating waypoints on a topo map or aerial imagery and then exporting them to my GPS unit. Saving and manipulating waypoint data is more problematical, and dealing with routes and tracks is a major headache. It seems as though some of these features were bolted on rather than integrated with the main program in a logical fashion. My experiences were with a Garmin GPS (60Cx); YMMV.

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USAPhotoMaps: Additional Capabilities

In addition to its primary function in retrieving, displaying and exporting TerraServer imagery like USGS topo maps and aerial imagery, USAPhotoMaps has some handy additional capabilities. I’ll talk about the GPS functions in another post, but here are some other useful functions available in USAPhotoMaps:

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Caching TerraServer Imagery For USAPhotoMaps

USAPhotoMaps offers a convenient and easy interface to TerraServer imagery (USGS topo maps, aerial photography). But it’s still a pain to have to sit and wait for imagery to be downloaded for a selected area you haven’t looked at before, since the data for that area can’t be permanently cached on the hard drive until it’s downloaded. If there’s a geographical area that you know you’ll want to have data “on call” for, there’s a free utility that will pre-cache TerraServer image data from that area on your hard drive for fast future access and retrieval by USAPhotoMaps.

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Georeferenced TerraServer Imagery With USAPhotoMaps

An earlier post described TerraClient, a program that lets you download large-area full-resolution USGS aerial photo imagery from the TerraServer website. That’s more convenient than downloading individual pieces from the USGS Seamless Server and then stitching them together, and has the additional advantage of letting you see the areas you’re selecting for download on-the-fly. But it has the disadvantage of producing images that aren’t “georeferenced”, i.e. they don’t come with the coordinate information needed to import and use them directly into a GIS viewer or editor.

There’s a free program called USAPhotoMaps that can create georeferenced TerraServer imagery for smaller geographic areas than TerraClient, and not just black-and-white aerial photos: it can also export georeferenced seamless color USGS topographic maps and high-resolution (0.15 to .65 meter) color aerial photos from selected urban areas. USAPhotoMaps has a far friendlier and faster interface than the USGS Seamless Server (which also offers this imagery in georeferenced format), and USAPhotoMaps has a bunch of additionalcapabilities that are easy and convenient to use. This post will deal with using TerraServer to view and export TerraServer imagery; its additional capabilities will be covered in future posts.

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