Hand-held GPS units typically have a limited amount of memory to store track points. My old Garmin eMap could hold only about 2000 trackpoints, while my newer 60Cx unit can hold up to 10000 trackpoints. There are also sometimes limits on the maximum number of trackpoints in a saved track; for example, the eMap limits the maximum number of trackpoints in a saved track to 250, while the Garmin limits you to 500. But suppose you have a long active track with greater than 500 points, and you’d like to save that track for future use in your GPS? Or you need to get the total number of trackpoints down to fit into your unit’s memory? There’s an easy way to “simplify” the track, reducing the total number of trackpoints without significantly affecting the track shape.
Archive for February, 2007 Page 2 of 4
I’ve posted about MapWindow in earlier posts on Shape2Earth (a shapefile to KML converter), and on reprojecting shapefiles from one coordinate system to another. So I figured it was time to take a longer look at some of MapWindow’s GIS capabilities, since it’s one of the best open source shapefile viewers and editors out there, and has many other useful functions. In addition, GIS novices might find this series useful as a general introduction to GIS programs, since it covers some of the basic operations applicable to other GIS programs as well.
Continue reading ‘Introduction To MapWindow GIS I – Shapefile Viewing’
I love rocks. I love dirt. And I love the maps that show them. A good geology map is visually like a weird hybrid between a Peter Max poster and Jackson Pollock drip painting, but also tells a story spanning several billion years of Earth’s history. I’ve found a few websites where you can find and download geology maps in a variety of formats.
Continue reading ‘Rocks And Dirt – Geology And Soil Maps Of The US And World’
Here’s a short post recapping my series on free (or cheap) ways to export shapefiles to Google Earth’s KML format:
Exporting Shapefiles To Google Earth I – Quick And Simple
Using GPS TrackMaker to quickly export point and line shapefiles into KML format. Not a lot of flexibility, though, and limited attribute export.
Export Shapefiles To Google Earth II – Shp2KML Converter
Shp2KML exports point, line and polygon shapefiles, with more attribute data than GPS TrackMaker. No ability to modify KML plots based on attribute data, limiting usefulness, especially for polygons.
Exporting Shapefiles To Google Earth III – shp2kml
shp2kml uses a wizard approach to export shapefile data to KML format. Allows you to export multiple attributes, and to vary plot color depending on attribute value. Has some problems with large shapefiles.
Exporting Shapefiles To Google Earth IV – Shape2Earth
The only paid solution here ($29.99), but by far the most flexible and powerful.
A Free And Easy Shapefile Coordinate Converter
Since the first two solutions above require the shapefile to be in Google Earth’s native coordinate system (geographic coordinates, WGS84 datum), here’s a great program to convert shapefiles in virtually any coordinate system to the right one for Google Earth.
Everyone else is blogging about the recent release of version 1.4 of NASA’s World Wind digital globe, so I might as well jump in as well. But I’ll do a listing of all the free available digital globes I’ve found.
Google Earth:Tops in terms of ease of use, user base, earth imagery, supported platforms (Win, Linux, Mac). Biggest disadvantage is that it’s not free for business or commercial use.
A worthy open-source alternative. Not as easy to use as Google Earth. Elevation database is superior, but baseline imagery isn’t as good. You can install a plug-in that allows you to use Microsoft’s Virtual Earth imagery, but that can only be used for non-commercial purposes. Other than that, it’s free for all uses, personal and commercial. Contains virtual globes for the Moon and Mars as well as Earth. USGS topo maps, digital orthoquads (1-meter black-and-white imagery), MODIS satellite data, Landsat data available in standard version. Supports KML and shapefiles. Extensive user community creating a wide variety of plug-ins to add additional capabilities. Currently Windows only, but a multi-platform Java version should be available later this year. Greater hardware requirements than Google Earth. Dapple is a specialized version for displaying geoscience data.
In addition to its original 2D view, Virtual Earth now has a 3D view. Has great 3D views of many cities, utilizing Microsoft’s extensive birds-eye view imagery. But only runs as a plug-in in Internet Explorer for now, and not as easy to use as Google Earth.
ArcGIS Explorer:
ESRI’s entry into the digital globe field. Lots of promise, especially as a vehicle for deploying data generated by other ESRI products, but not quite there yet. I can’t add much more to Stefan Geens excellent review. Not easy to find for download – try this link for directions (you’ll have to sign up for an ESRI Global Account). Windows only.
Descendent of TerraExplorer, one of the earliest 3D visualization tools. Works as a plug-in in Internet Explorer or Firefox; Windows only. Some interesting capabilities (built-in real-time GPS tracking, TrafficCam layer, custom weather, terrain tools, etc.); can plot shapefiles directly. Biggest weakness is the imagery, which appears to be mainly derived from USGS aerial photography. In cities like Tucson and San Francisco, with 0.25-meter color imagery, it looks great. Elsewhere, it looks like one-meter black-and-white digital orthoquads color-merged with Landsat imagery, which doesn’t look as good as Google Earth’s 2.4-meter color imagery.
My take: I use Google Earth as my main digital globe, since its ease of use and great imagery give it the edge. World Wind is a strong second, and I use it occasionally on my desktop; my laptop can’t handle it. Virtual Earth doesn’t have enough compelling content, or ease of use, to get me to use it that often. I’m keeping an eye on ArcGIS Explorer, but right now it’s not ready for prime time. SkyLine Globe loses major points for the quality of its imagery.
Many programs these days come with the built-in capability to produce output in the PDF format. For those that don’t, there’s a free program called PDFCreator that adds a printer driver to Windows; print to PDFCreator, and instead of hard copy output, your print results go into a standard PDF file, readable by Acrobat Reader or any other PDF-capable program. But what makes this a “GeoTool”?
The U.S. Census Bureau produces TIGER/Line vector data files (Topologically Integrated Geographic Encoding and Referencing). From the Census Bureau’s TIGER overview:
“The TIGER/Line files are a digital database of geographic features, such as roads, railroads, rivers, lakes, legal boundaries, census statistical boundaries, etc. covering the entire United States. The data base contains information about these features such as their location in latitude and longitude, the name, the type of feature, address ranges for most streets, the geographic relationship to other features, and other related information.”
These TIGER files are updated yearly, and contain some of the most current digital data for US streets and addresses. Most GIS programs can’t open TIGER vector files, and ESRI only has free TIGER data in shapefile format for the year 2000. Now a TIGER-to-shapefile converter that used to be a paid commercial program has been released as open source software, free for any use, along with a number of other useful TIGER and Census demographic data utilities.
Continue reading ‘Converting US Census TIGER Data Into Shapefiles For Free’
The Mapperz blog has a new post on ArcGIS 9.2′s Simplify Polygon feature:
“Simplifies a polygon by removing small fluctuations or extraneous bends from its boundary while preserving its essential shape.”
A nice tool to have to simplify polygon shapefiles with too high a level of detail. But suppose you don’t have ArcGIS 9.2 (at around $1500 list)? There’s a free web-based shapefile utility that does something similar.
