[GRASS-user] Re: v.rast.stats
Micha Silver
micha at arava.co.il
Tue Jun 22 10:26:48 EDT 2010
The raster resolution for the rainfall data was 0.25 degrees, or about
27 km. per pixel. So each pixel covers about 750 sq.km. The column with
the precip_sum will be mm/raster cell, or mm over an area of 750,000,000
sq.m.
Does that make more sense?
On 06/22/2010 03:57 PM, Sandile Gumede wrote:
> It's in mm/hr.
>
> Are these values normal, to me it seems like big values because they
> are ranging from 2000-4500, see below I just copied a few:
>
> 120795|4076||1|4076|4076|0|4076|0|0|0|4076
> 120796|4080||1|4080|4080|0|4080|0|0|0|4080
> 120797|4084||1|4084|4084|0|4084|0|0|0|4084
> 120798|4088||1|4088|4088|0|4088|0|0|0|4088
> 120799|4092||1|4092|4092|0|4092|0|0|0|4092
> 120800|4096||1|4096|4096|0|4096|0|0|0|4096
> 120801|4100||1|4100|4100|0|4100|0|0|0|4100
> 120802|4104||1|4104|4104|0|4104|0|0|0|4104
> 120803|4108||1|4108|4108|0|4108|0|0|0|4108
> 120804|4112||1|4112|4112|0|4112|0|0|0|4112
> 120805|4116||1|4116|4116|0|4116|0|0|0|4116
> 120806|4120||1|4120|4120|0|4120|0|0|0|4120
> 120807|4124||1|4124|4124|0|4124|0|0|0|4124
> 120808|4128||1|4128|4128|0|4128|0|0|0|4128
> 120809|4144||1|4144|4144|0|4144|0|0|0|4144
> 120810|4148||1|4148|4148|0|4148|0|0|0|4148
> 120811|4152||1|4152|4152|0|4152|0|0|0|4152
> 120812|4156||1|4156|4156|0|4156|0|0|0|4156
>
>
> 2010/6/22 Micha Silver <micha at arava.co.il <mailto:micha at arava.co.il>>
>
> On 22/06/2010 13:08, Sandile Gumede wrote:
>> Thanks, I finally got the results.
> That's good to hear.
>
>>
>> Now the question I would like to ask is that, from these columns
>> I got the values but which unit are these values are measured? Is
>> it (mm) or ?
> Well, that depends on the units of the raster. If the raster
> values are mm. then each column represents mm per *raster cell*.
> So if you have a rainfall raster with values in mm., and
> resolution of 10 meters, then the numbers in the columns are
> mm/100sq.m.
> --
> Micha
>
>
>>
>> On Sat, Jun 19, 2010 at 9:57 PM, Micha Silver <micha at arava.co.il
>> <mailto:micha at arava.co.il>> wrote:
>>
>> Hello Sandile:
>> I tried to duplicate your steps and it seems to work for me.
>> Here's what I did:
>>
>>
>> wget
>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tif
>> wget
>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tfw
>>
>> gdalinfo 3B42RT.2010032900.1day.tif
>> Driver: GTiff/GeoTIFF
>> Files: 3B42RT.2010032900.1day.tif
>> 3B42RT.2010032900.1day.tfw
>> Size is 1440, 480
>> Coordinate System is `'
>> Origin = (-180.000000000000000,60.000000000000000)
>> Pixel Size = (0.250000000000000,-0.250000000000000)
>> ....
>>
>> ---- Note: no projection info above ----
>>
>> ---- Now I use the -projwin option of gdal_translate to
>> select a small window
>> gdal_translate -a_srs EPSG:4326 -projwin 34.0 33.0 36.0 29.0
>> 3B42RT.2010032900.1day.tif rainfall_il.tif
>>
>> ---- GEOGCS entry now shows 4326 ----
>>
>> g.mapset map=ASTER_DEM loc=WGS84
>> ----- A location setup as EPSG:4326----
>>
>> r.in.gdal israel.tif out=rainfall_il
>>
>> r.univar rainfall_il
>> 100%
>> total null and non-null cells: 77760000
>>
>> total null cells: 0
>>
>> Of the non-null cells:
>> ----------------------
>> n: 77760000
>> minimum: 0
>> maximum: 34
>> range: 34
>> mean: 0.364583
>> mean of absolute values: 0.364583
>> standard deviation: 3.45241
>> variance: 11.9192
>> variation coefficient: 946.948 %
>> sum: 28350000
>>
>>
>> ----- Now using an existing catchment vector map ----
>> v.rast.stats vect=arava_wsheds rast=rainfall_il colpre=precip
>> v.info <http://v.info> -c arava_wsheds
>> Displaying column types/names for database connection of layer 1:
>> INTEGER|cat
>> CHARACTER|label
>> DOUBLE PRECISION|area_km
>> INTEGER|precip_n
>> DOUBLE PRECISION|precip_min
>> DOUBLE PRECISION|precip_max
>> DOUBLE PRECISION|precip_range
>> DOUBLE PRECISION|precip_mean
>> DOUBLE PRECISION|precip_stddev
>> DOUBLE PRECISION|precip_variance
>> DOUBLE PRECISION|precip_cf_var
>> DOUBLE PRECISION|precip_sum
>>
>> ---- and some values ----
>>
>> v.db.select arava_wsheds
>> cat|label|area_km|precip_n|precip_min|precip_max|precip_range|precip_mean|precip_stddev|precip_variance|precip_cf_var|precip_sum
>> 21|Jordan|1055.231692|2|0|0|0|0|0|0||0
>> 19|Hidan|987.811979|2|0|0|0|0|0|0||0
>> 28|Og|124.122969|||||||||
>> 36|Zarqa|273.606213|||||||||
>> 24|Kidron|122.460114|||||||||
>> 9|Darga|289.012122|||||||||
>> 6|Arugot|236.365116|1|0|0|0|0|0|0||0
>> 26|Mujib|1277.546513|2|0|0|0|0|0|0||0
>>
>> ---- (Many catchments have 0 or no value because of the small
>> region I chose. The global data is 1/4 degree resolution and
>> my region is only 2 deg E-W.)----
>>
>> HTH...
>> --
>> Micha
>>
>>
>>
>> On 06/17/2010 12:50 PM, Sandile Gumede wrote:
>>> Hi
>>>
>>> It is still giving me -NULL value error.
>>>
>>> Do you think maybe its the way I downloaded my rainfall
>>> data? This is the site where I downloaded my data sets_
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/ _and this data covers
>>> the whole world, the only thing I did was to clip a specific
>>> region (using coordinates) that is in South Africa to do my
>>> analysis. I used a bash script to download and project the
>>> data, see below:
>>>
>>>
>>> #!/bin/bash
>>>
>>> wget
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tif
>>> wget
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tfw
>>>
>>> gdal_translate -of GTiff -co "PROFILE=GeoTIFF" -co
>>> "INTERLEAVE=PIXEL" -co "COMPRESS=LZW" -co "TILED=YES" -a_srs
>>> EPSG:4326 -a_ullr 18.2987501 -33.6795831 19.1712501
>>> -34.3487498 3B42RT.2010032900.1day.tif TRMMLast1day.tif
>>>
>>>
>>>
>>>
>>> On Thu, Jun 17, 2010 at 8:41 AM, Sandile Gumede
>>> <akasandile at gmail.com <mailto:akasandile at gmail.com>> wrote:
>>>
>>> Hi
>>>
>>> It is still giving me -NULL value error.
>>>
>>> Do you think maybe its the way I downloaded my rainfall
>>> data? This is the site where I downloaded my data sets_
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/ _and this data
>>> covers the whole world, the only thing I did was to clip
>>> a specific region (using coordinates) that is in South
>>> Africa to do my analysis. I used a bash script to
>>> download and project the data, see below:
>>>
>>>
>>> #!/bin/bash
>>>
>>> wget
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tif
>>> wget
>>> ftp://trmmopen.gsfc.nasa.gov/pub/gis/3B42RT.2010032900.1day.tfw
>>>
>>> gdal_translate -of GTiff -co "PROFILE=GeoTIFF" -co
>>> "INTERLEAVE=PIXEL" -co "COMPRESS=LZW" -co "TILED=YES"
>>> -a_srs EPSG:4326 -a_ullr 18.2987501 -33.6795831
>>> 19.1712501 -34.3487498 3B42RT.2010032900.1day.tif
>>> TRMMLast1day.tif
>>>
>>>
>>>
>>> 2010/6/15 Micha Silver <micha at arava.co.il
>>> <mailto:micha at arava.co.il>>
>>>
>>> On 15/06/2010 14:35, Sandile Gumede wrote:
>>>> Hi
>>>> If I run g.region rast=rainfall -p, I get:
>>> OK, what you've done here is change the current
>>> region to match the raster "rainfall".
>>> Can you now try:
>>> v.rast.stats -c vect=catchments rast=rainfall
>>> pref=precip
>>>
>>>
>>>>
>>>> projection: 3 (Latitude-Longitude)
>>>> zone: 0
>>>> datum: wgs84
>>>> ellipsoid: wgs84
>>>> north: 33:40:46.49916S
>>>> south: 34:20:55.49928S
>>>> west: 18:17:55.50036E
>>>> east: 19:10:16.50036E
>>>> nsres: 0:00:05.01875
>>>> ewres: 0:00:02.18125
>>>> rows: 480
>>>> cols: 1440
>>>> cells: 691200
>>>>
>>>> and If I run r.univar rainfall, I get the following
>>>> output:
>>>>
>>>> 100%
>>>> total null and non-null cells: 691200
>>>> total null cells: 0
>>>>
>>>> Of the non-null cells:
>>>> ----------------------
>>>> n: 691200
>>>> minimum: 0
>>>> maximum: 3094
>>>> range: 3094
>>>> mean: 22.0228
>>>> mean of absolute values: 22.0228
>>>> standard deviation: 76.1639
>>>> variance: 5800.94
>>>> variation coefficient: 345.841 %
>>>> sum: 15222164
>>>>
>>>>
>>>>
>>>> On Tue, Jun 15, 2010 at 12:22 PM, Hamish
>>>> <hamish_b at yahoo.com <mailto:hamish_b at yahoo.com>> wrote:
>>>>
>>>> Micha wrote:
>>>> > The only unusual thing I notice above is that
>>>> the resolution settings
>>>> > for the raster are different N-S and E-W.
>>>> This came from the original
>>>> > tiff (see below) which also has rectangular
>>>> pixels,
>>>>
>>>> that is perfectly normal for a lat/lon map away
>>>> from the equator.
>>>> longitude scales a cos(lat).
>>>>
>>>>
>>>> > (the v.rast.stats module creates a temp
>>>> raster at the *current region's
>>>> > resolution* settings, which might be
>>>> different from this rainfall
>>>> > raster's rectangular resolution...)
>>>>
>>>> the results of:
>>>>
>>>> g.region -p rast=mapname
>>>> r.univar mapname
>>>>
>>>>
>>>> could help.
>>>>
>>>>
>>>> Hamish
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Kind Regards
>>>> TS Gumede
>>>> CSIR, Meraka Institute
>>>> 072 258 1650
>>>>
>>>>
>>>> This mail was received via Mail-SeCure System.
>>>
>>>
>>> --
>>> Micha Silver
>>> http://www.surfaces.co.il/
>>> Arava Development Co. +972-52-3665918
>>>
>>>
>>>
>>>
>>>
>>> --
>>> Kind Regards
>>> TS Gumede
>>> CSIR, Meraka Institute
>>> 072 258 1650
>>>
>>>
>>>
>>>
>>> --
>>> Kind Regards
>>> TS Gumede
>>> CSIR, Meraka Institute
>>> 072 258 1650
>>>
>>>
>>> This mail was received via Mail-SeCure System.
>>
>>
>> --
>> Micha Silver
>> Arava Development Co. +972-52-3665918
>> http://surfaces.co.il
>>
>>
>>
>>
>>
>>
>> --
>> Kind Regards
>> TS Gumede
>> CSIR, Meraka Institute
>> 072 258 1650
>>
>>
>> This mail was received via Mail-SeCure System.
>
>
> --
> Micha Silver
> http://www.surfaces.co.il/
> Arava Development Co. +972-52-3665918
>
>
>
>
>
> --
> Kind Regards
> TS Gumede
> CSIR, Meraka Institute
> 072 258 1650
>
>
> This mail was received via Mail-SeCure System.
--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
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