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Archive for the 'topographic maps' Category Page 2 of 6

Make Your Own Topo Maps For A Garmin GPS Unit

Well, the good news is that Garmin is finally starting to offer 1:24K scale US topographic maps for some of their GPS units. While they’ve had these maps for US National Parks in the East, Central and West for quite a while, they’re now issuing them for the US as a whole. These are different from the 1:100K Garmin topo maps available for a while, with the latest release coming in 2008. But there’s bad news as well:

– The datasets come on individual microSD cards, so they’re only compatible with units that support those cards

– Because they’re on microSD cards, you can’t load additional map data like CityNavigator or BlueChart data on the cards; you need to either do without or swap cards back and forth to get the dataset you want

– Cards cover various sections of the US, aren’t cheap ($100 list, typically available for about $60-70 street), and only a limited part of the US is currently covered:

(Note: Garmin also sells 1:100K topo maps on microSD cards, and you have to read the product description carefully to find that out; in any case, you’re almost always better off buying these 1:100K maps on a DVD; you can then upload selected maps to the GPS unit)

There are options that are cheaper, and cover areas not currently available from Garmin. The MiscJunk website has 1:24K topo maps for UT, MT and WY, with CA on the way, though there’s already a map file for the entire state of CA already available. Dan Blomberg’s  GPSFileDepot site has 1:24K topo mapsets for Arizona and Mississippi, and he’s automated the process to a point where I suspect more state mapsets will be coming in the future.

But Dan has also put up a full tutorial section on how to create your own 1:24K topo Garmin mapsets, with full links to data and software sources. While I wouldn’t describe the process as simple and easy, it can be done by anyone with reasonable computer skills. And even if you don’t need a full topo map, similar procedures can be used to create simple Garmin point, line and area maps from GPS and GIS data that can be overlaid on top of other mapsets.

Other data resources for creating your own Garmin GPS maps:

The Yahoo Map Authors forum

Creating Custom Topo Maps For A Garmin GPS

GPS Maps

Make Your Own GPS Maps From GIS Data (TravelByGPS website)

Make Your Own GPS Map

KeenPeople.Com Tutorial One, Tutorial Two

New Zealand Open GPS Project tutorial

Custom Maps For Garmin GPS Receiver Part One , Part Two

… and I hope to cover some other free options for creating Garmin GPS maps in the near future.

AZ Garmin Topo Maps And More From The GPS File Depot

Dan Bloomberg wrote to tell me of his new website, the GPS File Depot. Some useful stuff for GPS users, especially Garmin owners:

New GeoPDF Features

I’ve covered the free GeoPDF plugin for Adobe Acrobat and Reader before, but the latest version adds a lot of new features:

  • Create a point on the map, then open and view the corresponding point on Google Maps
  • A lot more coordinate systems supported, including MGRS, Lambert Conformal Conic, Mercator, etc.
  • Import and display shapefiles, re-projecting them on-the-fly
  • Import Google Earth KML/KMZ data; also CSV and GPX files
  • Annotate points with “sticky notes”, or with a GeoStamp symbol in various categories (incidents, infrastructure, operations)
  • Draw rectangles, polylines and polygons, and annotate them
  • Export annotated and imported data in shapefile format (automatically split into points, lines (arcs) and polygons)
  • Export annotated and imported data in KML format for use in Google Earth (another way to convert shapefiles to KML format)

One capability that’s still missing is the ability to export the view in georeferenced raster format, like GeoTiff; hope that’s coming soon.

The TerraGo Technologies tutorials page has a video tutorial on GeoPDF, and brief written tutorial with sample data for you to play around with. You can also download free USGS topo maps in GeoPDF format from the USGS Store’s Map Locater and Downloader. While these are still mostly in raster format, the next generation of USGS topo maps will come in vector GeoPDF format, letting you select from up to 37 different data layers.

Via Directions Magazine.

Worldwide Contour Lines In Google Maps' Terrain View

Google has just announced the addition of topographic contour lines to their Terrain view in Google Maps. It’s for the entire world, so I suspect they’re using SRTM 90-meter resolution data; not ideal, but not bad, either. Here’s Popocatepetl, just SE of Ciudad de Mexico:


You have to zoom in to at least the 1-mile / 2 km range for the contours to appear.

Reproject NOAA BSB Raster Navigation Charts And Export Them In TIFF Format

Yesterday, I posted about a NOAA site where you can download Raster Navigation Charts (RNC), maps of coastal and inland waterways. The charts are currently only available in BSB format, which many GIS programs can’t handle; I linked to a few free viewers that will let you view the maps, but not export them. They’re also only available in the Mercator NAD83 projection/datum. Peter Guth (the author of the terrain analysis GIS MicroDEM) let me know about a free utility available from NOAA called the Digital NOAA Nautical Chart Reprojector. It lets you re-project the BSB maps into one of 32 projections (e.g. geographic or UTM) and over 100 datums, then exports the chart in BSB, RAW or TIFF format with a world file; the latter virtually every GIS program and graphics editor can open. It looks like it was originally a command-line utility, since a DOS box pops up when you run the program, but it now comes with a GUI:

NOAA Chart Reprojector

The Input File and Output File dialog windows are a bit clumsy to use until you figure them out, but for the input file, you’re looking for the .kap file that came with the zip file you downloaded from the NOAA mapsite. Choose the desired output parameters at right, including choice of output file format (TIFF here), projection (UTM) and datum (WGS_84). The GUI doesn’t set the UTM zone automatically, but you’ll see the West and East Bounds for the map in the Input Info window at left, and can use those as a guide for setting the correct UTM zone with the Projection Parameters dropdown at right. In this case, clicking “Run” will create the TIF file specified as the output file, along with its worldfile. The file extension for that worldfile will be .tifw; if your GIS program doesn’t accept that, try changing it to the more-commonly seen .tfw extension.

NOAA also has a free extension called Chart Viewer that lets you open BSB charts natively in ESRI’s ArcView and ArcGIS, and Leica Geosystems’ Imagine.

Downloadable Updated NOAA Raster Navigation Charts

NOAA’s Office Of Coast Survey has downloadable copies of regularly-updated RNCs (Raster Navigation Charts). The updated charts are in BSB format, not supported by many GIS and graphic software programs, but there’s a list of links to free and demo software packages capable of displaying BSB files in georeferenced format (like Caris EasyView and GPSNavX). The site indicates that NOAA will issue GeoTiff versions of these charts at some unspecified point in the future, but those charts will not be as regularly updated as the BSB charts will. Selection is either by chart number or a graphical viewer (requires Java):


To choose a chart for downloading in the graphical viewer, click the “Selection Mode” button at the top, then click on the rectangle defining the chart area (clicking inside the rectangle does nothing). Click “Add To Cart” at left, which adds it to a list of charts to be downloaded. When you’re done selecting charts, click on “Place Order”, and follow the directions to get a zipped copy of the BSB chart (response time to the button-pushing may be slow):


Native map projection for the georeferencing is Mercator NAD83, in meters.

Full Index Of 1:250K US Army Topographic Maps

An earlier post featured a Google Earth KML file by Price Collins that indexed US Army topographic maps (1:250K) downloadable from the Perry-Castaneda Map library. At that time, 435 city maps and 413 1:250K quadrangles had been indexed, with each indexed map reference in the KML file containing a download link to the original map graphic file. Price writes to say that he has finished the index; it now includes 1785 topo quadrangles, covering large parts of Asia, Oceania, and Africa:



Also, 440 city maps; this picture shows those available for part of East Asia


Recoloring Or Modifying GeoTiff Images

I’ve been posting about various ways to extract and embed geographic metadata from GeoTiffs, image files that have coordinate information in them that can be used by GIS software to georeference the image, i.e. assigning a geographic location to each pixel. Here’s an example of how extracting geographic metadata (like a worldfile) from a GeoTiff might be useful.

USGS 1:24K topo maps are freely available on the Internet from a variety of locations, like LibreMap or the USGS Seamless Server. Maps of forested areas often include green shading to indicate the presence of tree vegetation, but this coloration has always struck me as inaccurate, superfluous, and interfering with reading more critical map features. The US Forest Service apparently feels the same way, as they have removed that green coloring from their updated versions of these topo maps. But if you have a digital topo map with this coloration, it’s possible to get rid of it without losing the geographic metadata.

I’ll start with the USGS 1:24K topo map of Kendrick Peak in Arizona, available here among other locations. This map has a large amount of green shading on it, which was arbitrary to begin with, and is now unfortunately out-of-date because of a serious fire a few years ago:


If I open this map in virtually any editor and save it, the geographic metadata will be lost. So the first step is to extract and save the full metadata using the libgeoGUI along with the libgeotiff utilities. Next, I’ll open it up in Photoshop Elements. Yes, Photoshop isn’t a “free geography tool”, but Photoshop Elements is a lot cheaper than the full version while still containing much of its functionality. If you look around on eBay or Google, you can often find a brand-new copy of an older version of Photoshop Elements very cheaply, $20-30. And it’s a useful tool to have for general image manipulation, including the purpose I’ll be describing here.

To keep the filesize down, USGS GeoTiff topo maps are often saved in “indexed color” mode, where there’s a limited palette of colors assigned to each byte of pixel information. If it is indexed, Photoshop will show “(Index)” at the top of the image window; if you go to Image => Mode, “Indexed Color” will be checked as well. As long as we’re in Image=>, I’ll select “Color Table”:


This shows the full palette of colors used in this topo map, only 13 in this case. If I double-click on the green, the color I want to get rid of, the color picker comes up:


This lets me modify that index color to whatever I want; in this case, setting R, G and B to 255 will turn everything colored green in the original to white. If I now save the newly-modified image as a TIF with a different name, the map area from above, with lots of green, will now look like this:


All the green has been transformed to white, while all the other colors were unaffected. One could have at the same time modified any of the other colors to white to make them disappear, or modified them to a different shade. If you create a modified color scheme you plan to use again, you can save that palette using the “Save” button in the Color Table window.

For images with standard RGB color instead of indexed color, you can use the “Replace Color” function (Enhance => Adjust Color => Replace Color) to perform a similar function.

Opening and saving the map image in Photoshop removes the geographic metadata, but as long as you don’t resize the image, you can use the metadata of the original image to convert this modified image into a GeoTiff. In libgeoGUI, specify the .gtf metadata file created in the first step as the input worldfile, specify the modified Tiff image with the green removed as the input Tiff, and enter a name for the output GeoTiff. Click the “Embed” button, and you now have a GeoTiff with the same geographic metadata as the original, but modified to remove the green. And this approach will work not just with color modifications; as long as you don’t resize the image, you can modify it any way you want, drawing lines and shapes, putting other images on top of it, etc., and then embed the metadata into the saved image when you’re done.