Thanks to the pandemic, GMDE Desktop has enjoyed a minor surge in popularity. My structural geology lab manual has several exercises that students can do to extract information from a geologic map. If you live anywhere near mappable geology, you can extend exercises into the field with GMDE Lite (for iPhone or iPad). This page provides hints of how to use these programs together. As students are more likely to have an iPhone than an iPad, these hints focus on GMDE Lite. Thus, you can start a project with your students in the lab and then have them field check or make new field observations on the outcrop in the same project. Note that development has largely ceased on GMDE Mobile as GMDE Lite can now do everything that Mobile can do (and more) in a simpler and more compact app.

(The above picture was taken by Paul Morgan in the field in SE Idaho.)

Preparing Base Materials

GMDE Lite and Desktop can use the same base materials for map based exercises: MBTiles for the base map and GridFloat digital elevation models (DEMs) for the topography. That means that an instructor only has to prepare one set of base materials which can then be distributed to students and will work without modification on all platforms. The desktop version of GMDE runs on Windows, Macs, and Linux computers; currently, GMDE Lite only runs on iPhones/iPads although that may change in the future.

MBTiles

Because you make your own base map, it can be anything you want. You are not confined to the limited range of base maps produced by online mapping companies. In many parts of the world, because of vegetation, satellite images are of limited use. At Cornell, we have been using LiDAR DEMs which, even when rendered as standard hillshade images, depict detail that students can observe directly in the field. To convert whatever base materials you wish to use for use in GMDE on a device, you will need to obtain and learn software that can convert any image into MBTiles format. That is because mobile devices have a small amount of RAM compared to desktop computers and thus they cannot hold an entire map image at full resolution in memory all at once. MBTiles are really a specialized SQLite database with many thousands of map tiles at different resolutions. GMDE reads the database and then puts the necessary tiles back together into what looks like a single image on the screen.

Several commercial programs, including ArcGIS and Global Mapper, as well as a few open source programs like GDAL/QGIS, can produce MBTiles files from your georeferenced image. I use a simple commercial program, MapTiler, for my own work. The free version of MapTiler will produce MBTiles with a watermark, but the $30 version will produce watermark-free MBTiles from images up to 10,000 by 10,000 pixels which is sufficient for many projects. MBTiles are a widely accepted format so that, even if you decide not to use GMDE, you will still be able to use MBTiles in an array of other mapping platforms.

Digital Elevation Models

GridFloat is a widely accepted format for DEMs that most GIS programs can read and write. Until a year ago, it was one of the standard formats that could be downloaded from the USGS National Elevation Dataset (NED). Unfortunately, the NED now provides downloads only as web-enhanced geotiffs which GMDE cannot read. You can, however, read geotiff DEMs with the free QGIS and QGIS can save the DEM in Band Interleaved Format (.BIL). BIL DEMs can be read by the desktop version of GMDE and that program can then trim and save the DEM as a GridFloat DEM.

Why is this so complicated?

There are several answers to this question: First, in the digital age, our tools are changing rapidly and that means learning new programs and formats so that we can do things that were impossible just a few years earlier. There is considerable power that comes with being able to go into the field with a DEM in your pocket and doing so means that we can now do computation in the field that was previously impossible. GMDE Lite/Mobile is the first suite of apps that allow you to do this. Second, DEMs are available in a dizzying array of formats and simplicity is simply not a concept associated with DEMs. Finally, I’m not a professional programmer; because I’m a scientist, once I find a solution that allows me to accomplish my research or teaching goals, I tend to think that is sufficient rather than finding solutions for all people under all circumstances.

Geological Data Interchange

Lite and Mobile use exactly the same format SQLite database to save their data and thus those database files are interchangeable between the two iOS apps. Although the GMDE Desktop uses a binary file format, it can import and export data in the SQLite database format used by Mobile and Lite. Furthermore, a database can be imported repeatedly and, each time, only the new observations (or more recently modified observations if the user specifies so), will be entered so that you do not end up with a bunch of duplicates. That means that one can easily move from one platform to another with minimal hassle.

Who Measured What?

GMDE allows each user to tag each observation with their name, which is entered in the settings screen or preferences dialog box of the version of GMDE on their PC/device. Thus, you as an instructor, can compile all of their data into a single GMDE project and still see who collected what observation. When you import a student’s database into your project, or one student imports another student’s into their project, the name of the original collector is maintained and is not easily editable.

StraboSpot Compatability

If you use StraboSpot (and you should), both GMDE Desktop and GMDE Lite can upload and download data from your account. When you start a project in GMDE Lite, you are given the option of using the StraboSpot lexicon for data types. You must initiate a GMDE Lite project specifying the StraboSpot Lexicon if you want to be able to upload and download data to/from your StraboSpot account. However, note that StraboSpot does not currently allow tagging of individual measurements with the name of the geologist who measured them so that part of a GMDE data record will not be preserved.

Import from Other Mapping Programs

GMDE Desktop and GMDE Lite can both read and parse GIS data in .KML and .GPX formats. .SHP files can be entered one of two ways: (1) Read the .SHP file into Google Earth and then save the result as a .KML file for import into GMDE. GMDE will ask you which attribute you want to use for the name of the feature and will record all of the additional attributes in the notes field of the datum. (2) Import the .SHP file into your StraboSpot account in a web browser. Then import the dataset from StraboSpot into your GMDE Project.

Export to Other Mapping Programs

GMDE can save it’s basic data types in .KML format which most mapping/GIS programs can read. If you need .SHP file output, you can upload your data to your StraboSpot account and then export from StraboSpot as a .SHP file.