NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.

To learn about what's going on, see About the Archive Site.

Re: [netcdf-java] Writing unsigned data to attributes

Hi Alex:
1) netcdf-3 does not support unsigned integer types. you need netcdf-4 for this.
2) CDM will support unsigned types if you add _Unsigned = "true" to the variables' attributes. But theres no way to indicate an attribute value is unsigned.
3) a valid range is applied to the underlying data, before anything else happens. for example heres a byte variable: 

byte time(time=255);
  :scale_factor = 10.0; // double
  :valid_range = -10, 10; // int

 data:
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, -128, -127, -126, -125, -124, -123, -122, -121, -120, -119, -118, -117, -116, -115, -114, -113, -112, -111, -110, -109, -108, -107, -106, -105, -104, -103, -102, -101, -100, -99, -98, -97, -96, -95, -94, -93, -92, -91, -90, -89, -88, -87, -86, -85, -84, -83, -82, -81, -80, -79, -78, -77, -76, -75, -74, -73, -72, -71, -70, -69, -68, -67, -66, -65, -64, -63, -62, -61, -60, -59, -58, -57, -56, -55, -54, -53, -52, -51, -50, -49, -48, -47, -46, -45, -44, -43, -42, -41, -40, -39, -38, -37, -36, -35, -34, -33, -32, -31, -30, -29, -28, -27, -26, -25, -24, -23, -22, -21, -20, -19, -18, -17, -16, -15, -14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4, -3, -2}
if you read that through the NetcdfDataset interface, which applies scale/offset, and makes values outside of the valid range into NaN, you get: 

double time(time=255);

 data:
{0.0, 10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 80.0, 90.0, 100.0, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, -100.0, -90.0, -80.0, -70.0, -60.0, -50.0, -40.0, -30.0, -20.0}
as you can see, the valid_range = -10, 10 is applied to the raw values, then the scale_factor is applied.
now if you add the _Unsigned = "true", and make the valid_range attribute values correct: 

byte time(time=255);
  :_Unsigned = "true";
  :scale_factor = 10.0; // double
  :valid_range = 10, 240; // int

you get:
{NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, 100.0, 110.0, 120.0, 130.0, 140.0, 150.0, 160.0, 170.0, 180.0, 190.0, 200.0, 210.0, 220.0, 230.0, 240.0, 250.0, 260.0, 270.0, 280.0, 290.0, 300.0, 310.0, 320.0, 330.0, 340.0, 350.0, 360.0, 370.0, 380.0, 390.0, 400.0, 410.0, 420.0, 430.0, 440.0, 450.0, 460.0, 470.0, 480.0, 490.0, 500.0, 510.0, 520.0, 530.0, 540.0, 550.0, 560.0, 570.0, 580.0, 590.0, 600.0, 610.0, 620.0, 630.0, 640.0, 650.0, 660.0, 670.0, 680.0, 690.0, 700.0, 710.0, 720.0, 730.0, 740.0, 750.0, 760.0, 770.0, 780.0, 790.0, 800.0, 810.0, 820.0, 830.0, 840.0, 850.0, 860.0, 870.0, 880.0, 890.0, 900.0, 910.0, 920.0, 930.0, 940.0, 950.0, 960.0, 970.0, 980.0, 990.0, 1000.0, 1010.0, 1020.0, 1030.0, 1040.0, 1050.0, 1060.0, 1070.0, 1080.0, 1090.0, 1100.0, 1110.0, 1120.0, 1130.0, 1140.0, 1150.0, 1160.0, 1170.0, 1180.0, 1190.0, 1200.0, 1210.0, 1220.0, 1230.0, 1240.0, 1250.0, 1260.0, 1270.0, 1280.0, 1290.0, 1300.0, 1310.0, 1320.0, 1330.0, 1340.0, 1350.0, 1360.0, 1370.0, 1380.0, 1390.0, 1400.0, 1410.0, 1420.0, 1430.0, 1440.0, 1450.0, 1460.0, 1470.0, 1480.0, 1490.0, 1500.0, 1510.0, 1520.0, 1530.0, 1540.0, 1550.0, 1560.0, 1570.0, 1580.0, 1590.0, 1600.0, 1610.0, 1620.0, 1630.0, 1640.0, 1650.0, 1660.0, 1670.0, 1680.0, 1690.0, 1700.0, 1710.0, 1720.0, 1730.0, 1740.0, 1750.0, 1760.0, 1770.0, 1780.0, 1790.0, 1800.0, 1810.0, 1820.0, 1830.0, 1840.0, 1850.0, 1860.0, 1870.0, 1880.0, 1890.0, 1900.0, 1910.0, 1920.0, 1930.0, 1940.0, 1950.0, 1960.0, 1970.0, 1980.0, 1990.0, 2000.0, 2010.0, 2020.0, 2030.0, 2040.0, 2050.0, 2060.0, 2070.0, 2080.0, 2090.0, 2100.0, 2110.0, 2120.0, 2130.0, 2140.0, 2150.0, 2160.0, 2170.0, 2180.0, 2190.0, 2200.0, 2210.0, 2220.0, 2230.0, 2240.0, 2250.0, 2260.0, 2270.0, 2280.0, 2290.0, 2300.0, 2310.0, 2320.0, 2330.0, 2340.0, 2350.0, 2360.0, 2370.0, 2380.0, 2390.0, 2400.0, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN, NaN} 


So thats the current state of affairs.


On 6/16/2013 8:05 PM, Alex Fraser wrote:

Hello,

I'm trying to write unsigned data to attributes, but I can't quite get it 
working. I've seen the mailing list threads on reading from unsigned 
attributes, but I haven't seen much discussion about writing.

Suppose I have an unsigned byte variable, and I want to set its `valid_range` 
attribute. I tried using `Array.setUnsigned`, but the values are still written 
as signed. In this case the valid range is 0..255, which comes out as 0..-1. 
This causes ToolsUI to read the variable as being empty.

I would just use shorts instead of bytes, but this approach does not seem to be 
reliable for all attributes: it fails for the `_FillValue` attribute which the 
nc4 IOSP says must be the same type as the variable.

I asked a question on StackOverflow; it has some simplified code in it:

     
http://stackoverflow.com/questions/17139391/netcdf-java-how-to-write-unsigned-attribute

Versions:
  - NetCDF-Java 4.3.16
  - libnetcdf 4.2.1
  - ToolsUI 4.3

Let me know if you need more information.

Cheers,
Alex
  • 2013 messages navigation, sorted by:
    1. Thread
    2. Subject
    3. Author
    4. Date
    5. ↑ Table Of Contents
  • Search the netcdf-java archives: