Re: [GRASS-user] dems from coordinate lists

Thu, 13 May 2010 10:46:58 -0700 

MS wrote:
If I follow correctly, instead of v.to.rast, you need to interpolate a raster DEM from the points. v.surf.rst produces nice results, but there are other interpolation modules as well in the raster category. 


That's the method I use also.
I start with:
v.in.ascii -z in=<ascii_file> z=3 out=vect_pts
This creates a 3D vector using the z column as the height values.
Now set the desired region:
g.region vect=vect_pts res=xxx

Choose the raster resolution that suits your needs. If the points in the 
ascii file are at 25 m spacing, then you probably could interpolate at 
10m-20m resolution (or better) with no problems.

Then:
v.surf.rst in=vect_pts layer=0 elev=dem ...

The layer=0 parameter indicates that you're using the 3D vector's z 
value for elevation.

--
Micha

Best regards,

Mark


On May 13, 2010, at 10:26 AM, Hanlie Pretorius 
<hanlie.pretor...@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_...@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_...@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_...@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_...@c83" output="dem_2628cc_25m" 
use="z"\

|     type="point,line,area" layer=1 value=1 rows=4096
|

+----------------------------------------------------------------------------+ 



Thanks
Hanlie
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--
Micha Silver
Arava Development Co. +972-52-3665918
http://www.surfaces.co.il


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