Thanks for the response. By center, I did not mean the geometric centroid, rather the center of intensity based on pixel values. For reference, if you’ve ever used IDRISI, something like their CENTER module:
“center
Compute mean center (weighted or not) of a point distribution and standard radius (the two dimensional equivalent of a standard deviation).”
I have worked with folks in the Geography department, and I know that this sort of thing is relatively easy mathematically, I just wanted to know if it was possible with GRASS 6.0 as it is.
Jason
On Jun 2, 2005, at 3:51 PM, Jonathan Greenberg wrote:
Jason:
What do you mean by center? Are you referring to a geometric centroid, or the brightest pixel value falling within a poly, or something else? Have you chatted with any of the RS people at BU? BU has one of the best remote sensing programs in the country (its also my alma mater).
–j
On 6/2/05 12:42 PM, “Jason Horn” <jhorn@bu.edu> wrote:
Does anyone know of a way to calculate the center of a shape in a raster file based on shape and pixel values? For example, imagine a NEXRAD RADAR image showing a storm cloud. Could GRASS be used to calculate the center of the cloud? I’m not having any luck finding a grass raster function to do this.
–
Jonathan A. Greenberg, PhD
NRC Research Associate
NASA Ames Research Center
MS 242-4
Moffett Field, CA 94035-1000
650-604-5896
AIM: jgrn307
MSN: jgrn307@hotmail.com
Not that I have the best answer for you (although I am interested in what you are doing with your reference to 'NEXRAD RADAR'); it seems to me that you may need to set some threshold to the raster to identify the cells and then do a raster to vector conversion from which you can identify the polygon centroids. Just a thought...
Regards,
Tom
Jason Horn wrote:
John,
Thanks for the response. By center, I did not mean the geometric centroid, rather the center of intensity based on pixel values. For reference, if you've ever used IDRISI, something like their CENTER module:
"center Compute mean center (weighted or not) of a point distribution and standard radius (the two dimensional equivalent of a standard deviation)."
I have worked with folks in the Geography department, and I know that this sort of thing is relatively easy mathematically, I just wanted to know if it was possible with GRASS 6.0 as it is.
- Jason
On Jun 2, 2005, at 3:51 PM, Jonathan Greenberg wrote:
Jason:
What do you mean by center? Are you referring to a geometric centroid, or the brightest pixel value falling within a poly, or something else? Have you chatted with any of the RS people at BU? BU has one of the best remote sensing programs in the country (its also my alma mater).
--j
On 6/2/05 12:42 PM, "Jason Horn" <jhorn@bu.edu <mailto:jhorn@bu.edu>> wrote:
Does anyone know of a way to calculate the center of a shape in a raster file based on shape and pixel values? For example, imagine a NEXRAD RADAR image showing a storm cloud. Could GRASS be used to calculate the center of the cloud? I'm not having any luck finding a grass raster function to do this.
Thanks,
- Jason
Jason Horn
Boston University Department of Biology
5 Cumington Street Boston, MA 02215
jhorn@bu.edu <mailto:jhorn@bu.edu>
office: 617 353 6987
cell: 401 588 2766
--
Jonathan A. Greenberg, PhD
NRC Research Associate
NASA Ames Research Center
MS 242-4
Moffett Field, CA 94035-1000
650-604-5896
AIM: jgrn307
MSN: jgrn307@hotmail.com <mailto:jgrn307@hotmail.com>
--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177
>> Does anyone know of a way to calculate the center of a shape in a
>> raster file based on shape and pixel values? For example, imagine
>> a NEXRAD RADAR image showing a storm cloud. Could GRASS be used
>> to calculate the center of the cloud? I'm not having any luck
>> finding a grass raster function to do this.
..
Thanks for the response. By center, I did not mean the geometric
centroid, rather the center of intensity based on pixel values.
..
I have worked with folks in the Geography department, and I know that
this sort of thing is relatively easy mathematically, I just wanted
to know if it was possible with GRASS 6.0 as it is.
View intensity as elevation and find the peaks.
e.g. visualize it in NVIZ.
Along that line of thought you can use the 'r.param.scale param=feature'
GRASS command to pull out the morphometric features: peaks, ridges,
passes, channels, pits and planes.
Or use r.slope.aspect to determine slope and curvature (1st & 2nd
derivatives) and find areas of no slope with negative curvature.
You'll then have to reclass your clouds to make them somewhat coherent,
and then label each distinct cloud with a max value taken from the area
of the peak in the orginial. If you want this last part to be automated
it might take some work, but I would think it is possible.
You'll then have to reclass your clouds to make them somewhat coherent,
and then label each distinct cloud with a max value taken from the area
of the peak in the orginial. If you want this last part to be automated
it might take some work, but I would think it is possible.
Perhaps with 'r.to.vect feature=area' after r.reclass.