I want to use GRASS (and QGIS) for analysis of water well locations in a town. The basic data has been provided thru (ARCWare) shapefiles. While input of data to create the well location point maps is no problem, the shapefile format embeds the “real” spatial location data in a proprietary file (the .shx index files). So I can input shapefile data, including the dBase attributes, I can’t get at the spatial locations; consequently I can’t correct for any location errors made as a result of data input mistakes. Is there a way to access these shapefile index files using GRASS? Or is there a way I can use that fact that I can produce a GRASS location map of points to obtain (say a table of) (x,y) relative to some know location on the map? If I could solve this problem, I could probably move the whole well data set out of shapefiles and into more accessible database system, e.g. MySql.
thanks,
–dick peskin
Richard L. Peskin, RLP Consulting, Londonderry, VT
http://www.rlpcon.com
http://www.caip.rutgers.edu/~peskin
Richard Peskin wrote:
I want to use GRASS (and QGIS) for analysis of water well locations in a town. The basic data has been provided thru (ARCWare) shapefiles. While input of data to create the well location point maps is no problem, the shapefile format embeds the "real" spatial location data in a proprietary file (the .shx index files). So I can input shapefile data, including the dBase attributes, I can't get at the spatial locations; consequently I can't correct for any location errors made as a result of data input mistakes. Is there a way to access these shapefile index files using GRASS? Or is there a way I can use that fact that I can produce a GRASS location map of points to obtain (say a table
If I understand correctly, you need the X-Y locations for a point shapefile as attributes.
I know of three approaches you can choose from:
1- In QGIS, grab Carson Farmer's "Calculate Geometry" plugin. It creates a new shapefile with XCOORD and YCOORD columns for point shapes.
2- In GRASS (assuming you have imported the shapefile as a GRASS vector) you can do v.out.ascii to get a text file with point coordinates. But you loose the other attributes.
3- Again in GRASS, add two columns to the vector table (v.db.addcol) with type 'double precision'. THen run v.to.db with the coor option to add X-Y values to the table in those new columns.
of) (x,y) relative to some know location on the map? If I could solve this problem, I could probably move the whole well data set out of shapefiles and into more accessible database system, e.g. MySql.
Shapefiles are probably the most accessible format there is. Every GIS program on the planet reads and writes shapefiles. The shapefile format has other drawbacks, but accessibility isn't one of them.
Cheers,
Micha
thanks,
--dick peskin