Hi,
I have a DTM I want to resample. The original data was in lat/lon SRS
which I re-projected to UTM and imported to GRASS GIS.
GRASS 6.4.3 (pampanga_wshed):~ > r.info ifsar_dtm
+----------------------------------------------------------------------------+
| Layer: ifsar_dtm Date: Mon Dec 22 10:07:06 2014 |
| Mapset: PERMANENT Login of Creator: maning |
| Location: pampanga_wshed |
| DataBase: /Users/maning/GRASSDATA/ |
| Title: ( ifsar_dtm ) |
| Timestamp: none |
|----------------------------------------------------------------------------|
| |
| Type of Map: raster Number of Categories: 255 |
| Data Type: FCELL |
| Rows: 44440 |
| Columns: 53950 |
| Total Cells: 2397538000 |
| Projection: UTM (zone 51) |
| N: 1842577.192205 S: 1620332.25097015 Res: 5.00101128 |
| E: 420942.75364933 W: 151243.07137293 Res: 4.99906733 |
| Range of data: min = -10000 max = 3.402823e+38 |
| |
| Data Description: |
| generated by r.in.gdal |
| |
| Comments: |
| r.in.gdal -e input="ifsar_dtm_utmz51n.vrt" output="ifsar_dtm" |
| |
+----------------------------------------------------------------------------+
Because of the origin SRS, the pixel size is not the same for ew_res and nw_res.
I tried running several resampling techniques to match the pixel size
equal to 5.
First, I tried r.resamp.interp.
g.region rast=ifsar_dtm_subset -pm
projection: 1 (UTM)
zone: 51
datum: wgs84
ellipsoid: wgs84
north: 1683792
south: 1645429
west: 220827
east: 268500
nsres: 5.00104289
ewres: 4.99926594
rows: 7671
cols: 9536
cells: 73150656
g.region res=5 -ap
projection: 1 (UTM)
zone: 51
datum: wgs84
ellipsoid: wgs84
north: 1683795
south: 1645425
west: 220825
east: 268500
nsres: 5
ewres: 5
rows: 7674
cols: 9535
cells: 73171590
r.resamp.interp input=ifsar_dtm_subset
output=ifsar_dtm_subset_interp_bic method=bicubic --overwrite
r.info ifsar_dtm_subset_interp_bic
+----------------------------------------------------------------------------+
| Layer: ifsar_dtm_subset_interp_bic Date: Tue Dec 23 13:17:51 2014 |
| Mapset: test1 Login of Creator: maning |
| Location: pampanga_wshed |
| DataBase: /Users/maning/GRASSDATA/ |
| Title: Resample by bicubic interpolation ( ifsar_dtm_subset_interp_bic |
| Timestamp: none |
|----------------------------------------------------------------------------|
| |
| Type of Map: raster Number of Categories: 255 |
| Data Type: DCELL |
| Rows: 7674 |
| Columns: 9535 |
| Total Cells: 73171590 |
| Projection: UTM (zone 51) |
| N: 1683795 S: 1645425 Res: 5 |
| E: 268500 W: 220825 Res: 5 |
| Range of data: min = -2.72093853362067 max = 1157.05376343899 |
| |
| Data Source: |
| ifsar_dtm_subset |
| Source map NS res: 5.00104289 EW res: 4.99926594 |
| |
| Data Description: |
| generated by r.resamp.interp |
| |
| Comments: |
| r.resamp.interp input="ifsar_dtm_subset" output="ifsar_dtm_subset_in\ |
| terp_bic" method="bicubic" |
| |
+----------------------------------------------------------------------------+
The output resolution matches.
Then, I tried r.resamp.rst.
g.region rast=ifsar_dtm_subset -pm
projection: 1 (UTM)
zone: 51
datum: wgs84
ellipsoid: wgs84
north: 1683792
south: 1645429
west: 220827
east: 268500
nsres: 5.00104289
ewres: 4.99926594
rows: 7671
cols: 9536
cells: 73150656
r.resamp.rst input=ifsar_dtm_subset elev=ifsar_dtm_subset_rrst
ew_res=5 ns_res=5 --overwrite
r.info ifsar_dtm_subset_rrst
+----------------------------------------------------------------------------+
| Layer: ifsar_dtm_subset_rrst Date: Tue Dec 23 14:13:49 2014 |
| Mapset: test1 Login of Creator: maning |
| Location: pampanga_wshed |
| DataBase: /Users/maning/GRASSDATA/ |
| Title: ( ifsar_dtm_subset_rrst ) |
| Timestamp: none |
|----------------------------------------------------------------------------|
| |
| Type of Map: raster Number of Categories: 255 |
| Data Type: FCELL |
| Rows: 7673 |
| Columns: 9535 |
| Total Cells: 73162055 |
| Projection: UTM (zone 51) |
| N: 1683792 S: 1645429 Res: 4.99973935 |
| E: 268500 W: 220827 Res: 4.99979025 |
| Range of data: min = -2.759012 max = 1157.082 |
| |
| Data Source: |
| raster map ifsar_dtm_subset |
| |
| |
| Data Description: |
| generated by r.resamp.rst |
| |
| Comments: |
| tension=617.194349 |
| dnorm=64.809407, zmult=1.000000 |
| KMAX=50, KMIN=35, errtotal=0.003577 |
| zmin_data=-2.600000, zmax_data=1157.017822 |
| zmin_int=-2.759012, zmax_int=1157.081551 |
| |
+----------------------------------------------------------------------------+
Really close but still doesn't match. To visualize the output I
created aspect layers for each respection resampling method, but both
layer still show checkerboard effects.
https://drive.google.com/file/d/0B-2WZQ1DwK_xbUpBTFJzcFdXV2M/view?usp=sharing
Any ideas on what I missed?
BTW, off topic, is there a way to limit the precision to say 3 decimal
places? Centimeter vertical unit should be more than enough for my
intended use.
--
cheers,
maning
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"Freedom is still the most radical idea of all" -N.Branden
blog: http://epsg4253.wordpress.com/
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