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Hello- I'm currently using the Resample tool to aggregate categorical vegetation data currently in 30x30m cells into larger blocks and am wondering how the majority values is calculated. Specifically, 1. What determines whether or not a cell values is included in the resampling? Does the Resample tool calculate a majority for the new, larger cell by the number of (smaller) cell centers contained within, or does it do a weighted majority based on the relative areas of (smaller) cells that fall within the new cells' boundaries? 2. What happens in case of a tie? The chances of this would be much smaller if Arc uses the weighted area method, but could definitely happen if just counting by cell centroids. If these questions are answered elsewhere, I apologize and would appreciate a link. Thanks for your help! Nathan
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12-05-2011
09:06 AM
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Hi Melita- Thanks for your quick response! I'm afraid there is no datum or spheroid information with the file metadata. I would have assumed it's geographic, but I'll see if I can get in touch with the originators and find out. The longitude values in the rotated grid range from -33.880 to 33.880 in increments of .440 degrees, symmetrically centered on 0. The latitude values in the rotated grid range from -28.380 to 28.380, also in increments of .440 degrees and symmetrically centered on 0. See attached for a table of congruent locations. I had to pull them together manually, and though I double-checked them, I'm afraid it's still possible that I made some transcription errors. Please let me know if you need anything else or come across something weird. Thanks again for your help! Nathan
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11-22-2011
10:03 AM
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Hello- Neither ArcGIS 9.3x or 10 seem to handle the importation of a netCDF file with a "rotated pole" coordinate system, listing the coordinate system as "unknown" in the data source tab. Barring an automatic fix allowing the program to correctly read these data, how would I go about manually defining a projection so that they display properly? The projection metadata provided in the netCDF file are as follows: char rotated_pole; :grid_mapping_name = "rotated_latitude_longitude"; :grid_north_pole_latitude = 42.5; // double :grid_north_pole_longitude = 83.0; // double :_CoordinateTransformType = "Projection"; :_CoordinateAxisTypes = "GeoX GeoY"; This is not enough information, in and of itself, to define a specific projection, which is probably why ArcGIS is having the problem. Looking at the CF Metadata convention (specifically Appendix F), it appears that a third parameter of north_pole_grid_longitude defaults to 0 if not specified. I think these three parameters should be enough to manually define the projection, but I'm unsure of how to do so. In the 'Define Projection' tool, what projected coordinate system should I select as a base? There are no "rotated_pole" or "rotated_latitude_longitude" or "arctic somethingorother"... Oh, and the purpose of defining the coordinate system is more so that I can project other things into the same coordinate system (for example a polygon representing the extent of the studyarea so that I can clip the netCDF data). I apologize if this question has been asked/answered elsewhere, and thanks for your time! Sincerely, Nathan Elliott
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11-21-2011
09:01 AM
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