[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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