Hi Nikos, Thank you for reply. I don't have exact NDVI band statistics but I have statistics of NDVI difference maps. We calculated NDVI's of different times for same area and then subtract one from another. I mean we have NDVI of 2000 and 2010 for the same area and we subtracted NDVI 2000 from NDVI 2010. I can send statistics of original NDVI files tomorrow. These are statistics of difference maps. I attached them to my post.
I'm not sure about 'different pixel inclusion rules' but I think 'spatial resolution and extent' is same for both, you can see it in stat files I sent. Also we didn't use MASK in both. Thanks. 2013/1/14 Nikos Alexandris <n...@nikosalexandris.net> > On Monday 14 of January 2013 01:03:42 Gökçen Güner wrote: > > Hi, > > Hi! > > > This will not be a specific GRASS question. My friend and I tried to > > calculate NDVIs of same data set and results seem same to us. But > checking > > statistics of each output we saw that statistics are very different. I > > mean, median, mean, std.dev values of Grass output and Erdas output are > > different. > > How different? Can you please post exact numbers if that is ok? If > differences > are minor, you can simply ignore them :-) > > > We couldn't find an explanation for this situation. What can be > > the reason for this? > > There are reasons. For example, different pixel inclusion rules (of course > I > have in mind border-near pixels). Other reasons might be the spatial > resolution and extent (remember, GRASS-GIS is strict with that) and the > presence of a MASK. > > The experts might give better clues. > > Best, Nikos > > > PS: > > For NDVI, we used this formula: (NIR_Band - RED_Band) / (NIR_Band + > > RED_Band) > > Note, grass7 has i.vi for this job :-)
Driver: GDAL provider HFA Erdas Imagine Images (.img) Dataset Description G:\differenceimagendvi2000-2005.img Band 1 LAYER_TYPE=athematic STATISTICS_EXCLUDEDVALUES= STATISTICS_HISTOBINVALUES=1176|49|0|49|0|0|49|0|0|0|0|0|0|0|0|98|147|0|0|0|0|0|0|49|0|0|0|0|0|0|49|98|245|343|49|98|49|98|196|147|196|343|441|441|735|980|1225|1911|3234|2744|2107|1764|2009|1421|3675|5929|10094|12054|15141|17689|22393|23275|30233|23765|40229|35084|36701|36407|37240|38171|35133|34104|36113|32536|32536|30821|31752|30576|28763|29449|30772|29596|27930|28665|25970|20580|19747|19747|19257|18130|20482|20874|20923|18816|20433|19502|23373|18963|21658|23912|26803|28910|26558|27440|27048|28322|26999|26852|25284|30772|31654|34986|39249|40425|45864|52822|62573|64827|77322|84623|101332|109711|130781|143619|178605|206976|245784|292530|14293447|453103|590450|759451|1044876|1397529|1853719|2317896|2881298|3451903|3910641|3886631|3258745|2289917|1465884|944475|653513|468293|373821|300860|248479|212464|187719|165473|149646|134554|120393|111475|100450|88788|87171|78008|76195|67865|60858|59584|55566|51646|52479|45864|44982|44100|41454|43071|42826|44100|47040|48118|51107|55174|52283|48902|46158|38465|33271|29106|29547|23912|22393|20237|17493|19796|19355|16856|24010|22785|24402|22001|25284|23520|25921|30233|31850|31801|35035|38563|42532|34202|29204|23961|25431|29449|23912|22246|14112|5586|1470|3430|10731|7399|5880|8722|6272|4116|735|490|441|196|343|245|392|245|98|98|343|147|98|294|49|147|98|196|98|147|196|49|147|147|147|196|147|98|49|98|98|49|98|153027| STATISTICS_HISTOMAX=2 STATISTICS_HISTOMIN=-2 STATISTICS_HISTONUMBINS=256 STATISTICS_MAXIMUM=2 STATISTICS_MEAN=0.12239306770747 STATISTICS_MEDIAN=0.125 STATISTICS_MINIMUM=-2 STATISTICS_MODE=0 STATISTICS_SKIPFACTORX=7 STATISTICS_SKIPFACTORY=7 STATISTICS_STDDEV=0.25389091378836 Dimensions: X: 7651 Y: 7031 Bands: 1 Origin: 601785,4.25612e+06 Pixel Size: 30,-30 No Data Value 2.14748e+09 Data Type: GDT_Float32 - Thirty two bit floating point Pyramid overviews: Layer Spatial Reference System: +proj=utm +zone=36 +datum=WGS84 +units=m +no_defs Layer Extent (layer original source projection): 601785.0000000000000000,4045185.0000000000000000 : 831315.0000000000000000,4256115.0000000000000000 Band Band 1 Band No 1 No Stats No stats collected yet
Driver: GDAL provider GTiff GeoTIFF Dataset Description D:\gis\grassData\etm\ndviDiff.TIF AREA_OR_POINT=Area Band 1 COLOR_TABLE_RULE_RGB_0=-1.234239e+000 -7.590971e-001 255 255 0 0 255 0 COLOR_TABLE_RULE_RGB_1=-7.590971e-001 -2.839548e-001 0 255 0 0 255 255 COLOR_TABLE_RULE_RGB_2=-2.839548e-001 1.911875e-001 0 255 255 0 0 255 COLOR_TABLE_RULE_RGB_3=1.911875e-001 6.663298e-001 0 0 255 255 0 255 COLOR_TABLE_RULE_RGB_4=6.663298e-001 1.141472e+000 255 0 255 255 0 0 COLOR_TABLE_RULES_COUNT=5 LAYER_TYPE=athematic STATISTICS_MAXIMUM=0.97340524196625 STATISTICS_MEAN=0.00097015961553423 STATISTICS_MINIMUM=-1.1823400259018 STATISTICS_STDDEV=0.14471098370192 Dimensions: X: 8081 Y: 7121 Bands: 1 Origin: 601785,4.25702e+06 Pixel Size: 30,-30 No Data Value -3.40282e+38 Data Type: GDT_Float32 - Thirty two bit floating point Pyramid overviews: Layer Spatial Reference System: +proj=utm +zone=36 +datum=WGS84 +units=m +no_defs Layer Extent (layer original source projection): 601785.0000000000000000,4043385.0000000000000000 : 844215.0000000000000000,4257015.0000000000000000 Band Band 1 Band No 1 Min Val -1.1823400259 Max Val 0.9734052420 Range 2.1557452679 Mean 0.0009701596 Sum of squares 0.0000000000 Standard Deviation 0.1447109837 Sum of all cells 0.0000000000 Cell Count 57544801
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