|Home | Embedded / Signal Processing | Device control library | Visualization | Contacts/Links|
When planning a longer trip to yet unknown places, you might be left with some topological questions: how to get there, where are the next cities, where are the mountains. Often, you can not obtain detailed maps from local suppliers, even worse, some countries do not even provide maps for various reasons. So, one has to sometimes bite into the sour apple and make his/her own map, since the apple should not be to sour, it is not desirable to pay large amounts of money for raw data. Well, this is not necessary, as there are free sources, listed below.
Table 1. Data sources with links
The standard formats like TIFF, JPG, GIF, etc you might already know. However, there are some wicked compressed formats like MrSID that deal well with large tiled image data. Further, some geographical data is often attached to the images, either in a separate text file or in separate channels, according to extension standards. For example, the GeoTIFF extension stores Latitude, Longitude and mapping in a separate TIFF chunk within the image file. This is very useful when importing the data into GIS (geo information system) software, as you're no longer left with calibrating your corner points. For manual tracing and viewing, MrSID is a nice format, as the appropriate viewers often support fast zooming in. However, for automatical tracing or if you want to obtain specific vegetation indices, you may rather want to use the raw data from the Landsat site. Note that the amount of data to be downloaded is significantly higher as when using a MrSID file.
When making a map, you may want to have an overlay of all the above data that is interesting to you, like height and vegetation index. Normally, the data comes in different formats, one is mapped in WGS84 (degrees in longitude and latitude), one in UTM (universal transverse mercator), one is orthonormalized on a local coordinate system. You know the problem: How to map a sphere surface to a flat square plane without the least errors. We will not get into the details of projection, but tell you how the problem is basically tackled from a non expert map creator's point of view. A bunch of smart people have solved the problem for you with libraries that are used quite often within several GIS software packages. These libraries are called proj4 and GeoTrans. No worries, you will not have to write your own programs. The next step is a presentation of a selection of software that does the job pretty well.
These are the programs used to create or extract map data from the various sources:
Table 2. Program list with download links
To first deal with the above mentioned mapping problem, we have to find a common coordinate system to translate the data into. In this case, we use the UTM coordinate systems.
Now this is the overview over the steps you have to take towards a proper map:
After you have downloaded the DEM data from the SRTM data sources listed in Table 1, “Data sources with links”, import them into SAGA via > > > > . Note that you may have to load the module DLLs first via > .
Then, you have to do the UTM projection conversion from WGS84 to the UTM zone. Normally, the zone number is automatically derived from the WGS coordinates. Choose Modules>Projection>Grid>Proj4 (Grid) and make sure you have set the parameters in the following dialog according to the values in Table 3, “proj4 to UTM parameters”.
Table 3. proj4 to UTM parameters
In the following query, the UTM zone will be displayed. If your zone
lies on the southern hemisphere, activate the 'South' check box. The
last dialog in the conversion process will ask you about the resolution
of the resulting grid. The unit is the one specified in the first
dialog (default: meters). A grid size of 30 m (per pixel) is a
recommended value. You can alternatively choose the resolution of an
existing grid by using another
Last but not least you can generate the contours via Figure 1, “Processing the height data in SAGA”.> > > from Grid. The shading is done via > > . As an example result, see
To check whether your converted data matches with a downloaded landsat MrSID image, go through the following steps:
There are two ways of tracing the data, either manually or automatically. Manual tracing can be well done from within GPS trackmaker, or you can use existing GPS data from road trips or forest walks.
We will here cover automatical tracing of coast lines and vegetation attributes. To do a proper analysis of that data, we recommend reading of the Landsat Tutorial.
Here is again a quick list of steps you have to take in order to obtain vector data from landsat images. For all image manipulation, we use GIMP.
Finally we come to the point where you would want to visualize your data. In this example, we use the GPS Trackmaker for output, because it is by far the neatest program for quick editing of data.
The contour lines can be exported from SAGA GIS and be reimported to GPS Trackmaker using the SHP format. For the background image, the already mentioned EMF format is very useful, since the vector data can be rescaled with no pixelization effects and normally takes less memory space. However note that the EMF format does not contain world coordinate information. You will have to calibrate the corner points manually in GPS trackmaker.
The map can then be printed from within GPS trackmaker, however the printing functionality is somewhat limited. If you want a professional output of the map, you will have to look at tools from ESRI, etc.