[GRASS-user] Re: dems from coordinate lists
Hanlie Pretorius
hanlie.pretorius at gmail.com
Fri May 14 05:49:36 EDT 2010
Hi Jamie,
Thanks, this worked perfectly.
Regards
Hanlie
2010/5/13, Jamie Adams <jaadfoo at gmail.com>:
> Did you adjust the region also? To do this properly, you need to first scan
> the file using r.in.xyz to get the extents. I'd also use the shell style
> output.
>
> r.in.xyz -sg input="2628cc.ORT.xyz" output="dem_2628cc_25m_xyz
>
> Should return something like:
>
> n=1000 s=500 w=500 e=1000 t=### b=###
> (you can ignore the t & b output)
>
> This is the extent of the points, which are going to be the center of the
> output pixels. Since the region is defined as pixel edge, you need to
> expand the region 1/2 a pixel in each direction to ensure the points are in
> the center of the pixel. At 25m spacing, your region should be set as:
>
> g.region n=1012.5 s=487.5 w=487.5 e=1012.5 res=25
>
> - Jamie
>
> On Thu, May 13, 2010 at 9:02 AM, Hanlie Pretorius <
> hanlie.pretorius at gmail.com> wrote:
>
>> Hi Jamie,
>>
>> I tried r.in.xyz:
>> (r.in.xyz input="2628cc.ORT.xyz" output="dem_2628cc_25m_xyz"
>> method="mean" type="FCELL" x=1 y=2 z=3 zscale=1.0 percent=100)
>>
>> but I still get the rows of no data in the result.
>>
>> Hanlie
>>
>>
>> >
>> > 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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