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bio website barry.rowlingson.com
location Lancaster, United Kingdom
age 48
visits member for 4 years, 2 months
seen 4 hours ago

Here I am.


12h
comment Extract values from raster into points: data loss using extract function from raster package
Edit your question to set up an example like I've done that illustrates the problem. Is it just a case that your new sample cell areas are different, and you've forgotten that the original raster is km/**per unit area** and you need to scale up by the change in cell area? I don't know, because you haven't given us any code.
Nov
20
comment Extracting raster values with polylines in QGIS
How is "average slope" defined? It might just be the height difference from start to finish divided total distance, in which case you only need to sample the height at two points. Otherwise there's some calculus involved which you can probably estimate with finite steps...
Nov
20
answered Extract values from raster into points: data loss using extract function from raster package
Nov
20
comment Extract values from raster into points: data loss using extract function from raster package
@CincoSauces yes. But how can the sum of the values of a small number of points sampled over a grid ever be anything but less than the sum of the grid cells? We really need to see some code and some clarification. I don't understand why this Q has been upvoted.
Nov
20
comment Extract values from raster into points: data loss using extract function from raster package
If you are only sampling 49,000 points then obviously they are going to sum to less than 66,000 cells. What did you expect, and can you give us a reproducible example maybe using random data on a much smaller grid?
Nov
13
comment Saving text labels out of qgis
If the text is an attribute of the point features then its in the DBF part of the shapefile. Try opening the .DBF in a spreadsheet program (I don't know if MS Office can read it, but Libre Office can).
Nov
10
comment R custom color theme in levelplot
What are you going to do with this colour ramp once you've go it? Different plot functions have different ways of mapping values to colours. ggplot2 uses its own scales concept, base graphics uses a fixed palette (usually) and so on...
Nov
9
comment 1km circles around lat-long-points in many places in world
I have a problem with "exactly 1000m" and the phrase "circle-polygons". Your circle-polygons need infinite segments to be exactly 1000m, and converting to UTM (or any other planar system) is going to introduce even more errors. Be careful with the use of "exact".
Nov
9
answered How can i use Kriging inside a Postgis database?
Nov
9
comment How can i use Kriging inside a Postgis database?
Do you want to interpolate from just four measurement locations? That only gives you six points (4*3/2) for working out the covariance for the Kriging equations. It'll be rubbish.
Nov
8
comment conversion of .img to binary file using R
This isn't a very clear question.
Nov
7
revised basic gpx editor
added 205 characters in body
Nov
7
comment How can i use Kriging inside a Postgis database?
If you want to do this on the server side you just need PL/R and some custom scripts, but you'd have trouble plotting variograms and all that. Not easy. Much easier to pull the data out of the DB and work with R on the client side.
Nov
7
answered basic gpx editor
Nov
7
comment basic gpx editor
Do you want to do this on your mobile (US: "cell phone") or on a laptop/desktop?
Oct
22
answered Best practice to perform raster map algebra in open source web GIS?
Oct
22
comment Determine mudflats area from remote sensing images
unsupervised classification is where the algorithm itself works out the classes by looking at the pixels and "clustering" by intensity in the bands. It might not find "mudflats" as a category, or it might find several categories for "mudflats" since smooth mudflats might look different to more rippled mudflats or slightly damp mudflats. In a supervised classification you'd put samples of all those in the "mudflat" training set.
Oct
22
answered Determine mudflats area from remote sensing images
Oct
17
comment scatterplot of two rasters in R
I'm never sure when raw rasters work and when you need values() so I played it cautious without testing!
Oct
17
comment scatterplot of two rasters in R
I suspect you mean "coefficient of determination"?