Buen Dia. @German_Skena
In 1992 I spent a week with some geologists and petroleum engineers in Las Herras to work a joint problem. Our Spanish speaker got sick, real sick. None of the Argentinian technologists spoke English. We spent the week drawing formula and diagrams on a blackboard; I understand the problems being in the field. No cell phones or translation programs then. I knew enough Spanish to read a restaurant menu and order a beer (dos cerveza certainly).
As amazing as the mapping tools available on a cell phone; you still need a WIFI or data connection to display a map using GPS coordinates. Access to the map requires the Internet. Sometimes you are in a remote location and cannot get a data link. You can always get GPS data and record it for later playback to a map. The GPS receiver in the cell does not use the Internet and can write the coordinates to TinyDB, a database that is within the Android device for analysis later.
You mentioned several issues you would like to address using cell phones and tablets. I'll comment on some of them. Some problems are solvable using App Inventor.
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Soil Analysis - have you seen this solution to a triangle diagram? What is the appropriate function? - Soil Texture Triangle? - #21 by ABG . You might find it useful. As a graduate student, I spent part of a summer collecting soil samples; surveying the sample loations, then taking the samples back to school to sieve and classify. Yuk.
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"you will not have a computer or internet".-- gps works and so does the internal Android database; use them to take your field notes.
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"I want to use the compass, take the data, store and then plot." You can. The plotting you can do when you get home. The compass in an Android is not very accurate or reliable, use your Brunton. The location coordinates can be accurate to several meters in a cell phone, I used to do this with a plane table alidade (later a transit), then I got a job.
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"IF YOU MAKE A COMPASS APP, TAKE THE DATA, STORE AND SHARE THE POINTS.. Well. The amount of ERROR reduce almost TO 0." Yes, you can combine datasets. You can also transfer the data to a spreadsheet and use a Google Spreadsheet on your PC at home. You can even consolidate (merge) the data from your 10 students.
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i want to add the STEREOPLOTTING section. Why? Take a photo of the outcrop, note the azimuth of the camera, save to the Canvas, then use the drawing tools to sketch in the fault and other features. I don't know what you want to do in the Stereo plotting section. Just save the data, draw a sketch, take a photo, plot at home. Another Android programming tool can possibly create and rotate a 3d object Draw and rotate 3d bodies | B4X Programming Forum because it has access to drawing libraries that AI does not have. Perhaps that might be something you would want to do to visualize faults etc. Here is a thesis paper that discusses using App Inventor to work with 3d objects. https://dspace.mit.edu/bitstream/handle/1721.1/124236/1144934688-MIT.pdf?sequence=1&isAllowed=y
Here is another paper regarding 3D rotations
Using App Inventor extensions to implement rotation
Perhaps there is a way to visualize using App Inventor after all. Can it be adapted to your purposes German?
Use your cell and its programs but don't forget to use your notebook too.
Some of what you hope to do is extremely complex. I once wrote a program for a laptop to planimeter, later made a small app to contour a surface from data points. Not sure I could reproduce it with Android using App Inventor (its drawing capabilities are limited). AI's graphics stink and are awkward to use but some researchers have found ways to do some interesting things.
Some things can be done with App Inventor; some are simply too complex.
Good luck.