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bio website staff.acecrc.org.au/~mdsumner
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visits member for 4 years, 2 months
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R, Manifold, GDAL, also interested in Python, topojson/D3 and NetCDF/HDF


Nov
14
answered Export band names with NetCDF file in R
Nov
13
comment Mapping NetCDF CF Mercator parameters to GDAL
Check this out: remotesensing.org/geotiff/proj_list/mercator_1sp.html Notably "PROJ.4 does not support a latitude of natural origin other than the equator", otherwise I thinkyour presumptions are right. (Apart from ignoring false easting/northing - you cannot do that if not zero, but it's a trivial adjustment). Anyway, in my experience it's rare for NetCDF to explicitly store non-longlat explicitly, so keen to learn more if you can share more details from the header.
Nov
10
awarded  Yearling
Nov
6
comment Count values greater than 0 in SpatialPolygonsDataframe R
Quite. There's no room for more than one "layer" in a SpatialPolygonsDataFrame in my sp-dictionary. I think you mean nrow(spolydf) > 100. Yeah? Please clarify the rest I cannot make sense of it.
Nov
2
comment Prior art on rhumb line and great ellipse areas?
Ok thanks, we are on the same page at least. I don't see a problem with this, it's a limitation in most systems that the "curve" must be stored as an approximation rather than be generated on the fly from a rhumb or gc rule. I am interested to see if there will be any answers.
Nov
2
comment Prior art on rhumb line and great ellipse areas?
Equal area not angle. The extra vertices are not for calculating per se, just for representing the region in the right way. I don't get your overall task really, I don't see how it's any different to calculating area normally.
Nov
2
comment How to import NetCDF to PostGIS (or GeoTIFF)
And so for your question, the details matter! Please post a ncdump or gdalinfo (or equivalent) description of the file or variable within a file you wish to import.
Nov
2
comment How to import NetCDF to PostGIS (or GeoTIFF)
Is the problem you are having the import per se or different aspects of that import's interpretation? There's no end to the problems you can get when NetCDF meets GIS, the file spec is just so open it can completely depend on specifics for individual cases. So conversion to GeoTIFF simply puts the issue one step away without solving it.
Nov
2
comment Prior art on rhumb line and great ellipse areas?
Standard practice would be to do the calcs in an appropriately local equal area projection. Right? The only real issue is whether your shapes have sensible topology and/or sufficient vertices to represent whatever the thing is correctly when you transform, or draw it in that projection. (But this a constant concern that is basically a broken part of most/all GIS, and a key knowledge base item of the "expert-practitioner").
Nov
1
comment How convert a Modis hdf to txt with lat long using a command line
Use gdal_translate from an appropriate system build of GDAL. What is EVI?
Oct
28
comment Working with MODIS in R
Jeff: well only if rgdal has also been built with HDF.
Oct
27
comment las2dem issue - while generating a DEM raster cells with no data are being generated
Is this a licenced copy of lastools?
Oct
26
comment Unable to install ECW support on lubuntu 14.04
There's a stray space in the symbolic link step before "/libNCSEcw.so". I can't remove it because apparently fixing just one character is not allowed.
Oct
21
comment Definitive list of Proj4 supported coordinate systems
The command line options for "proj" -lp and -le and -ld list the available coordinate systems, ellipsoids and datums. It's not possible to list every possible combination of proj coordinate systems and all parameters (obviously) but those three lists give you a huge range of components to define what you need.
Oct
19
comment Converting LANDSAT-8 TIFF to matrix, data frame, or SpatialGridDataFrame formates
Read it it with the readGDAL function in the rgdal package, which returns a SpatialGridDataFrame.
Oct
17
comment Generic Grid to Coordinate System
Which manufacturer?
Oct
17
comment warping and outputting coordinates of GeoTiff data: advice and error checking
Warping inherently creates a new grid of points, it's got nothing to do with the original.
Oct
14
comment How to create a map colored by distance to nearest point in R
Would counties be small enough for your small areas to carry the message?
Oct
14
comment Convert PNG to GeoTiff using GDAL
Can you show us the image and tell the story of where it's from? I wrote this to R-Sig-Geo the other day for a similar problem: stat.ethz.ch/pipermail/r-sig-geo/2014-October/021814.html. Someone with the experience can help, but you'll need more information about where the image comes from and probably ultimately what it looks like.
Oct
14
comment Geometric Operations in GIS Systems
Short answer is just that it depends. Any "straight line" between two vertices will traverse a different line on the Earth depending on the projection. This is not going to affect operations that are relevant only to the vertices, but any time two segments (lines or polygon edges) cross then the interpretation will be different in different coordinate systems. There's no universal right answer, it depends on how the data is set up and what the intention of the operation is. There are many poor choices of projection, so choosing the right one is just as important as using one.