Picking up the thread of archaeological surveying creation, we will make a brief introduction to the import and conversion of data with three free desktop Sig: G vSig , Quantum Gis and Openjump . We intend to prove that, at least in archeology, the free Sig are already a real alternative to drawing with CAD, and also in most cases are even more appropriate to treat archaeological information.
In free GIS book cited a handful of desktop tools open source, we have selected the three mentioned since our understand offer very good features with a short learning curve in environments very intuitive, but can say that there are others which can surely perform the same operations, such as uDig or Kosmo.
The common case that we consider as an example of a text file with the coordinates of the points that define two walls (obtained for example by total station), and the goal is to try to import and get a shape to layer formats polygons of the structures. The text file (puntos.csv) has the following format: ID
, Y, X, Z, UE
01,4457259.920,700638.981,1491.596 ,1001
02,4457260.682,700639.694,1491.463 ,1001
03,4457261.404,700640.534,1491.052 ,1001
04,4457260.781,700641.137,1491.050 ,1001
05,4457259.967,700640.398,1491.403 ,1001
06,4457259.217,700639.987,1491.617 ,1001
07,4457259.508,700639.223,1491.609 ,1001
08,4457258.539,700641.365,1491.561 ,1002
09,4457259.434,700641.483,1491.438 ,1002
10,4457260.153,700642.030,1491.022 ,1002
11,4457260.095,700643.001,1491.110 ,1002
12,4457257.773,700642.812,1491.509 , 1002
already said that, although by different methods, all three programs allowed to import them quite easily.
In G vSig the first step is to add a table with data delimited csv format. For the proper import had to replace separators "," a ";" and got the table without problems. Subsequently, from a light load a layer of Events (menu "View") indicating the fields that contain x and y coordinates, to visualize and our points already displayed. This layer keep it in shape format (menu Layer> export to> shp ") and loaded (the event layer can not perform the following operation, so you have to turn it into shape). Finally points automatically converted into polygons through dialogue "Creating shp geometries derived" (menu "Layer"). This utility is very interesting because it allows us to control what points we want to be part of different polygons on a layer, and it can also generate lines from our points. Thus, we can actually import a layer with all points earned that represent walls, excavation lines, dimensions, materials, etc. and control step by step the creation of different polygons, lines, in the target layer.
Q In Gis uantum , the process is also really easy (even more), through the use of two supplements: the "Create a layer from a delimited text file" and "Points2one" so that must be enabled before proceeding. With the first snap you get a dialog where you must indicate the details of file formats to import and layer name to generate. Once the charged layer by the second-ons, "Points2one" we get the polygons (or lines) from the points. If the field also indicate that identifies different polygons ("Create output features based on input field"), in our case the "EU", we get separated by their labels.
Finally, to achieve equivalent results by O penjump the process is quite similar, except that we must adapt our format text wkt. The method is well explained in the excellent tutorial the Archaelogical Digital Documentation Project, so we avoid the details to focus on one aspect in which openjump highlights: the possibility of achieving layer contains different types of entities, ie points, lines and polygons through its own format, jump gml (JML).
As you know, the most widespread vector format sig is the shape, despite having the limitation that a layer in this format can contain only one type of entity, that is, or single points, or just single lines or polygons .
Openjump
This ability must be carefully evaluating. On the one hand, the fact is that it can be very useful to represent in a single layer different types of entities (dimensions, excavation lines, structures on the other hand ...), but JML format is a file type that can be opened in other sig, so it should only be used if it will work exclusively with Openjump.
probably be with me that it is better to sacrifice some versatility for compatibility, as apparently seen, the three programs are effective in the import and management of such data, and therefore more than decide on one or another it is best to use each of them according to the specific problem we face.
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