Thursday, 15 August 2013
OpenJUMP: query to extract single points from a general vector layer
today I am working on data elaboration of an archaeological excavation. I decided to record a short videotutorial to show how to perform a very simple query in OpenJUMP (which is a topic I am often asked to explain during lessons about archeology and open source). Before to start, I'll write a short introduction regarding the processing of this data, just to understand why I need to perform this kind of query.
I worked on this excavations collecting all the data in a local system (with simple 3D Cartesian coordinates), because the job was an emergency archeology project and I did not have the time to set up a geographic coordinate system on the field, before the construction site began. Just at the and of the excavation, I could come with a RTK GPS, to collect some Ground Control Points (GCP) in UTM WGS84. This is the reason why in this time, when I am processing the data, I had to put together all the daily total station downloads in a single cvs file, which I georeferenced in OpenJUMP, using the GCP I collected with the GPS. The problem is that now I will have to separate again the single points, grouping them according to their function (e.g. points for photomapping of area 1, height points of the same area, points for SfM georeferencing, find-points and so on...). To do this operation, I will simply use OpenJUMp (where I loaded and georeferenced the csv file), performing a query on the attribute (the name) of cumulative vector layer , which will tell me where are the the points I need. In this way I can select in the GIS the features I am looking for and put them in a new vector level, copying the db schema of the cumulative layer (name, y, x, z, code). At the end of the process, I will have single separated vector files which I will use in the next steps of data processing (photomapping, 3D, ecc...).
Here is the videotutorial I uploaded in the ArcheOS tutorila wiki (rom Insbruck University):
I hope it was useful, have a nice day!