I have a shapefile of a map that is the outline of a number of islands. I would like to convert the lines into polygons (ie all islands filled in) using GRASS. I searched on how to do this with GRASS but just got some very brief and vague suggestions ... but I gave it a go anyway ....
use v.in.ogr to import the shapefile into grass And view the result (I'm using QGIS to do this): Looks good.
v.clean input=g_hwp_p1 output=g_hwp_p1_clean tool=break,snap thresh=10,10 v.type input=g_hwp_p1_clean output=g_hwp_p1_clean_type type=line,boundary v.centroids input=g_hwp_p1_clean_type output=g_hwp_p1_clean_type_centroids
This didn't work which is not surprising as I don't really understand what I'm doing.
V.info says that...
g_hwp_p1 has 892 lines g_hwp_p1_clean has 892 lines g_hwp_p1_clean_type has 892 boundaries g_hwp_p1_clean_type_centroids has 892 boundaries (0 centroids, 0 areas, 0 islands)
Also v.type reports:
892 incorrect boundaries.
And v.centroids reports:
0 features modified.
The final output looks much like the input (just an outline).
Can anyone spot what I'm doing wrong? Does anyone know what the correct parameters should be?
I also tried this in QGIS using the lines-to-polygon fTool but this didn't do a very good job of it (it didn't fill in the whole islands but just seemed to add little polygons round the edge).
Screenshoy of hwp_p1 .... https://docs.google.com/leaf?id=0B93lksnTC7_cN2Q5YTNiMjEtZjY4OS00ZTYwLWIxMDAtYzBlNmY1M2U1MGRl&hl=en_US
And a close-up of a small Island - it forms a closed loop.. https://docs.google.com/leaf?id=0B93lksnTC7_cZjQ1ZDU4ZGQtMWNmMC00ZjNiLWFiZmEtM2MyMDE0MmYzODQ5&hl=en_US