Latest Contributions by AnnaUkkola

Hello, I created a new color ramp using the Preset Color Ramp option. The map displays fine in my chosen colours and the new color ramp shows up in the pop-up menu. However, in the table of contents the color ramp that is displayed for this layer is whatever the default is and not the new preset color ramp. I have the same problem if I try to create a legend for the map, I do not have the correct colour bar displayed in the legend but the default. Any ideas how to get round this so I can add a meaningful legend to the map? many thanks! ... View more

Hello, I was wondering how I can change the NoData value of a raster dataset? When I created the raster from an XY table (text file) ArcMap set the NoData value to the default -3.40282346639e+038. However, I am trying to calculate zonal statistics for the raster dataset and want NoData values to be ignored in the calculations. Missing values are set to -9999 in the original dataset so I need to have these values ignored. How can I change this? Is it possible to set the NoData value when I create the raster or can it only be done afterwards? I've tried using the Con and Set Null tools in Spatial Analyst to change the NoData value but without success. One problem I've had using these tools is that when I open the SQL window to write the expression no fields show up. My raster dataset has fields "stretched value" and "pixel value", I've tried typing these into SQL, but the output is a strange 'stripy' raster with big blocks missing. Any help appreciated! ... View more

Hello, I am trying to produce zonal statistics as table using a polygon shapefile and a raster as input. First I used 'extract by mask' to extract the appropriate cells from a global raster dataset and this works fine as ArcMap extracts all (and only) the cells that have their centre within the polygons. However, when I produce the zonal stats the results are not correct. Too many or too few cells are included in the count and the sum and other statistics are wrong for some (but not all) polygons. Both the shapefile and raster are in the same coordinate system (GCS WGS 1984) and I use the default settings for this tool. Does anyone have any ideas what might be causing this error? Any help appreciated! ... View more

Hello, I am trying to extract raster cells using the Extract by Mask function. As expected, it shifts the cells slightly when I don't set the processing extent (->snap raster) to the original raster. However, when I do set it to avoid the shifting ArcMap shifts the cells massively (see attached file). For example Central America is now in the Amazon... I've worked with these data before without any problems so I am extremely puzzled by what is going on. I've tried different shapefiles as the mask but none of them seem to work (I either get the massive shift or ArcMap produces an empty raster). I am using version 10.0 and had Service Pack 2 installed recently. If anyone has any suggestions what might be causing the problem I would be extremely grateful. [ATTACH=CONFIG]11594[/ATTACH] ... View more

Hello, I have created a netcdf file in matlab and am trying to display and process it in ArcMap. I need to overlay it with a shapefile that uses the GCS_WGS_1984 projection and has longitude ranging from -180 to 180. My original netcdf file had a longitude vector ranging from 0.25 to 359.75 so only the positive longitudes could be overlaid with the shapefile (see image attached, netcdf file in blue). I changed the longitude vector to the following format: 0.25 0.75 .. .. .. 179.75 -179.75 .. .. .. -0.75 -0.25 I was hoping this would allow me to overlay the shapefile and the netcdf file, and also have the zero latitude (greenwich) in the middle instead of the pacific. The file I created displays fine in Panoply so it is not corrupted or have a faulty coordinate system. However, ArcMap only displays one data point when I open the file and the attribute table only has one line with information FID 0, Shape point,  Runoff 0. When I try to convert this netcdf file into a raster I get the following error: ERROR 000276: one or both dimensions have variable spacing in their coordinate values. This happens despite the fact that the longitude vector is spaced at regular 0.5 degree intervals and has 720 values just like the original vector. I'm confused as to why ArcMap cannot read this file and have run out of ideas on how to overlay the two datasets. The latitude vector is clearly fine but I do not know how I should format longitude for ArcMap to understand it and display negative (western) longitudes in the left and positive (eastern) longitudes in the right. Any help would be greatly appreciated! ... View more

Hello, I am using Spatial Analyst -> Extraction -> Extract by mask  to extract cells from a raster grid using a polygon shapefile as  the mask. I was hoping to find out what condition ArcMap uses to perform the extraction and how it selects which cells to extract when they lie on the shapefile boundary (i.e. when part of the cell is within the polygon and part of it outside it). Does ArcMap extract the cells if a certain percentage of the boundary cell is located inside the shapefile polygon or what criteria does it use exactly? I need this information for academic research purposes. I am using default environment settings. thank you in advance! ... View more

Hi, I'm having trouble with the spatial analyst tool 'extract by mask'. I converted a point dataset into a raster (points at 0.5 degree intervals) and used that raster dataset to extract by mask. I extracted raster cells based on river basin shapefiles (irregular polygons) as masks. This works fine as such but some of the basin shapefiles are too small or or a wrong shape and consequently no raster cells are extracted for these. I have attached a figure of the different layers for clarification. I need each river basin to have at least one corresponding raster cell so could you please suggest a way to get round this problem? Is is possible to adjust the area that the shapefile needs to cover in each raster cell in order to be extracted  (e.g. assuming that at the moment it is only picked up if it covers at least 50% of the raster cell)? Or is there possible another tool I could use? Thank you for the help. ... View more