Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Hi Nikos, Yes I didn't noticed the differences until Sylvain said, too :) I did g.region you are right, I did it to the imported maps, I wrote it in my last post. What i don't know is how to do same thing in Erdas but this is grass mailing list so my friend will ask about this in erdas forums. 2013/1/14 Nikos Alexandris > g.region rast=ImportedRasterMap > ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Güner: Hi Güner! > @Nikos: I'll send information about maps tonight. I'll send 'r.describe -r' > output also. I think it might not be necessary. As Sylvain pointed-out, and I confirm this (had a quick look in the morning), the reported layere dimensions are different! Check it out please. This might be the single root of evil in this case. > @Sylvain: Thank you, I didn't noticed the differences, my friend might had > done histogram strecthing over results, so this may be the reason for -2/2 > thing, I will check this. > By the way I'm not sure how we can make data to have same layer extent and > dimension in both programs. I didn't do a special thing before calculation, > I just used g.region and r.mapcalc methods. How exactly? After importing you need to g.region rast=ImportedRasterMap or similar. [rest deleted] Best, Nikos ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Hi, @Nikos: I'll send information about maps tonight. I'll send 'r.describe -r' output also. @Sylvain: Thank you, I didn't noticed the differences, my friend might had done histogram strecthing over results, so this may be the reason for -2/2 thing, I will check this. By the way I'm not sure how we can make data to have same layer extent and dimension in both programs. I didn't do a special thing before calculation, I just used g.region and r.mapcalc methods. 2013/1/14 Sylvain Maillard > Hi, > > a quick look at the stats files show some differences: > - "Dimensions" > - "Layer Extent" > - not the same range of data (from -2 to 2 in ERDAS ? oO) > > so that's totally logical to get different mean and stdev ... > > take care to use exactly the same extent/res when you are comparing 2 > files ;) > > > cheers, > Sylvain > > > > 2013/1/14 Nikos Alexandris > >> Gökçen Güner: >> >> > > 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. >> >> What kind of images are those, if I may ask? Which sensor? >> >> > > 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. >> >> > > 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. >> >> Also, >> >> what about NULL or NoData cells? How does ERDAS deal with them -- I don't >> remember now. How are they defined, if they exist, in your image? >> >> What does "r.describe -r" return for the data set(s) in question? >> >> Thanks, Nikos >> ___ >> grass-user mailing list >> grass-user@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/grass-user >> >> > > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Hi, a quick look at the stats files show some differences: - "Dimensions" - "Layer Extent" - not the same range of data (from -2 to 2 in ERDAS ? oO) so that's totally logical to get different mean and stdev ... take care to use exactly the same extent/res when you are comparing 2 files ;) cheers, Sylvain 2013/1/14 Nikos Alexandris > Gökçen Güner: > > > > 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. > > What kind of images are those, if I may ask? Which sensor? > > > > 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. > > > > 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. > > Also, > > what about NULL or NoData cells? How does ERDAS deal with them -- I don't > remember now. How are they defined, if they exist, in your image? > > What does "r.describe -r" return for the data set(s) in question? > > Thanks, Nikos > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Gökçen Güner: > > 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. What kind of images are those, if I may ask? Which sensor? > > 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. > > 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. Also, what about NULL or NoData cells? How does ERDAS deal with them -- I don't remember now. How are they defined, if they exist, in your image? What does "r.describe -r" return for the data set(s) in question? Thanks, Nikos signature.asc Description: This is a digitally signed message part. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
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 > 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.,4045185. : 831315.,4256115. 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): 601785.000
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
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 :-) signature.asc Description: This is a digitally signed message part. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
Hi, We did both statistics calculation using QGis because ERDAS couldn't calculate statistics for Grass output (or we couldn't do it). I'm sure that Grass output is floating point map but I'll check Erdas one. Thanks 2013/1/14 Angelos Tzotsos > On 01/14/2013 01:03 AM, Gökçen Güner wrote: > > 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. We couldn't find an explanation for this situation. What can be > the reason for this? > > PS: > For NDVI, we used this formula: (NIR_Band - RED_Band) / (NIR_Band + > RED_Band) > > > > > ___ > grass-user mailing > listgrass-user@lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/grass-user > > > Hi, > > Please make sure that the output images are of the same type in both cases > and that your statistic calculation method is the same. > NDVI is a float (or double) result if your initial data are integers > (usually they are). > Perhaps one of your images is automatically converted to 8 bit integer > type? > > Cheers, > Angelos > > -- > Angelos Tzotsos > Remote Sensing Laboratory > National Technical University of Athenshttp://users.ntua.gr/tzotsos > > ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
On 01/14/2013 01:03 AM, Gökçen Güner wrote: 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. We couldn't find an explanation for this situation. What can be the reason for this? PS: For NDVI, we used this formula: (NIR_Band - RED_Band) / (NIR_Band + RED_Band) ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user Hi, Please make sure that the output images are of the same type in both cases and that your statistic calculation method is the same. NDVI is a float (or double) result if your initial data are integers (usually they are). Perhaps one of your images is automatically converted to 8 bit integer type? Cheers, Angelos -- Angelos Tzotsos Remote Sensing Laboratory National Technical University of Athens http://users.ntua.gr/tzotsos ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics
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. We couldn't find an explanation for this situation. What can be the reason for this? PS: For NDVI, we used this formula: (NIR_Band - RED_Band) / (NIR_Band + RED_Band) ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
