preparing GPS coordinates for processing in gis

Question

I'm currently working on a masters in archaeology, using QGIS to examine some palaeolithic sites. I created a database with the site coordinates, which I collected from looking at bibliographies of site reports, emailing scholars, a couple of university databases and good old google earth. As I used a variety of sources, my coordinates are in a variety of formats so for example;

Grotte de Fees; Chatelperron 46°24'42''N 03°38'18''E, 
La Ferrassie                 44,955 0,941 
Grotte du Trou de la Chevre  45.325239  0.588272
Aranbaltza                   503017.16, 4805322.50 (in UTM 30N) 
Grotte de la Verpilliere II  632908mE, 5185383mN   (31T) 
Dzeraza Skala                554026,73; Y: 1243588,633 (S-JTSK_Krovak_East_North)

So basically it looks like a complete mess.

I've also noticed that entering the coordinates into google earth can give different locations if I separate the x and y with a comma or a full stop. I want to convert everything to WGS84 before starting my analysis. WHat is the best way of doing this?

Answer 1

I would separate the data into the various coordinate systems first and try to standardize the data in each as much as possible. Create a separate file for each coordinate system. If the data is in a spreadsheet, have a separate sheet for each coordinate system. Then you can use a single sheet to create a layer (shapefile or feature class) for each that is in that coordinate system. You will likely need to experiment a little bit to get the files in the exact format that you want (as you mentioned commas vs. periods make a difference).

Next you will need to project the data to WGS 84. I'm assuming you mean to use Geographic coordinates with that datum. The method for doing the projection will depend on what software you are using (at this point you did not specify).

With QGIS you can follow these instructions. See 7.1.3 in particular which covers saving a dataset to another CRS. Here you are essentially doing a "Save As" on the dataset and changing the output coordinate system (CRS).

If you are using ArcMap, you can do essentially the same thing using Data->Export by right-clicking the layer in the table of contents or you can use the "Project" tool under "Projections and Transformations".

Answer 2

I like JB's answer above but will add two things.

If the point locations are for a 'general overview' map then it might suffice to simply pan to each area where the site is located and create a point. At a large scale one point might cover an entire city or town as a visual representation. In that case the exact coordinates are not important at relatively large scales.

If they need to be dead on an alternative to JB's might be a custom script such as the one from this SE Q/A. It seems simple enough, but the bulk of the work is like JB said sorting and organizing and standardizing.

from pyproj import Proj, transform

inProj = Proj(init='epsg:3857')
outProj = Proj(init='epsg:4326')
x1,y1 = -11705274.6374,4826473.6922
x2,y2 = transform(inProj,outProj,x1,y1)
print x2,y2