[GRASS-user] dems from coordinate lists
Jamie Adams
jaadfoo at gmail.com
Thu May 13 10:58:05 EDT 2010
You want the points to represent cell centers so you need to expand your
region 1/2 pixel in all four directions. Also look at using r.in.xyz, it
works directly on this type of data.
Jamie
On Thu, May 13, 2010 at 7:26 AM, Hanlie Pretorius <
hanlie.pretorius at gmail.com> wrote:
> Hi,
>
> I've obtained DEMs in text files with columns X, Y and Z at 25m
> spacing. The first three entries in the text file are:
>
> -----
> X,Y,Z
> 99550,2.9883e+06,1473.47
> 99550,2.98828e+06,1473.57
> 99550,2.98825e+06,1473.63
> -----
>
> To me it seems the easiest way to import these is the following:
>
> 1. v.in.ascii
>
> 2. Set the region to the extents of new vector file and the resolution to
> 25m.
>
> 3. v.to.rast.
>
>
> This 'works' but I get horizontal strips of no data in my raster DEM
> at 25m spacings.
>
> Also, when I look at the raster and the vector layer together, the
> vector points are not always on the edges of the raster cells.
>
> Can someone perhaps help me to fix this?
>
> g.region:
>
> projection: 99 (Transverse Mercator)
> zone: 0
> datum: ** unknown (default: WGS84) **
> ellipsoid: wgs84
> north: 2988300
> south: 2959850
> west: 74300
> east: 99550
> nsres: 25
> ewres: 25
> rows: 1138
> cols: 1010
> cells: 1149380
>
> v.info:
>
> +----------------------------------------------------------------------------+
> | Layer: dem_2628cc_25m at C83
> | Mapset: C83
> | Location: sa_tm_19deg_E
> | Database: C:\Hanlie\grassdata
> | Title:
> | Map scale: 1:1
> | Map format: native
> | Name of creator: Administrator
> | Organization:
> | Source date: Thu May 13 16:06:07 2010
>
> |----------------------------------------------------------------------------|
> | Type of Map: vector (level: 2)
> |
> | Number of points: 1151529 Number of areas: 0
> | Number of lines: 0 Number of islands: 0
> | Number of boundaries: 0 Number of faces: 0
> | Number of centroids: 0 Number of kernels: 0
> |
> | Map is 3D: Yes
> | Number of dblinks: 0
> |
> | Projection: Transverse Mercator
> | N: 2988300 S: 2959850
> | E: 99550 W: 74300
> | B: 1429.79 T: 1740.2
> |
> | Digitization threshold: 0
> | Comments:
> |
>
> +----------------------------------------------------------------------------+
>
> r.info:
>
>
> +----------------------------------------------------------------------------+
> | Layer: dem_2628cc_25m at C83 Date: Thu May 13 16:15:50 2010
> | Mapset: C83 Login of Creator: Administrator
> | Location: sa_tm_19deg_E
> | DataBase: C:\Hanlie\grassdata
> | Title: Categories ( dem_2628cc_25m )
> | Timestamp: none
>
> |----------------------------------------------------------------------------|
> |
> |
> | Type of Map: raster Number of Categories: 0
> | Data Type: DCELL
> | Rows: 1138
> | Columns: 1010
> | Total Cells: 1149380
> | Projection: Transverse Mercator
> | N: 2988300 S: 2959850 Res: 25
> | E: 99550 W: 74300 Res: 25
> | Range of data: min = 1429.850000 max = 1739.410000
> |
> | Data Source:
> | Vector Map: dem_2628cc_25m at C83 in mapset C83
> | Original scale from vector map: 1:1
> |
> | Data Description:
> | generated by v.to.rast
> |
> | Comments:
> | v.to.rast input="dem_2628cc_25m at C83" output="dem_2628cc_25m"
> use="z"\
> | type="point,line,area" layer=1 value=1 rows=4096
> |
>
> +----------------------------------------------------------------------------+
>
> Thanks
> Hanlie
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