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
