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18h
comment QGIS: Turning Filter On and Off
You can also get around this by using a rule-based renderer, or use a SpatiaLite layer which allows editing while a filter is applied. See gis.stackexchange.com/questions/32533/… for more.
Jan
10
comment Is Spatialite Really Slow?
Note that the latest versions of Spatialite implement a Virtual Spatial Index, and the above syntax no longer works. The WHERE clause would be rewriten as WHERE map2.ROWID in ( SELECT ROWID from SpatialIndex WHERE f_table_name = 'map1' AND search_frame = map1.geometry)
Jun
6
comment How to prevent data scraping in a web map?
Thanks Russel, I think that a combination of a strongly worded legal statement (mileage may vary) and this approach will probably work in this case. I found a useful tutorial at SWITCH2OSM
Jun
6
comment How to prevent data scraping in a web map?
Mapperz, obfuscating the javascript would be useful for protecting the programming logic (which is not needed in this case), but my understanding is that the data will still be easily copied. At least this is my conclusion from testing an online obfuscator.
Jun
5
comment How to prevent data scraping in a web map?
I always appreciate your creative solutions, whuber. In this case it's probably not quite what I need (points should be clickable with popups) but there might well be other scenarios where this would be worth pursuing.
Mar
28
comment Getting Transparent Circles with Heatmap Plugin
Here's a useful explanation of why it's not recommended to do analysis in Pseudo Mercator (also known as Web Mercator): blogs.esri.com/esri/arcgis/2010/03/05/… If you are only after the "heatmap effect" and not worried about the spatial meaning (x points within kernel radius), then you can get away with generating heatmaps with data in EPSG:3857 projection. If those numbers are important, then it's best to reproject.
Mar
28
comment Getting Transparent Circles with Heatmap Plugin
I'm glad you got it working! I usually do it this way: 1) load the points as WGS84, 2) save that layer in a UTM projection (if the area fits within one UTM zone, otherwise some appropriate local projection). 3) create the heatmap using the projected points as input 4) reproject resulting heatmap to pseudo mercator using raster warp 5) load openlayers. You shouldn't have any alignment problems that way, and you're not doing analysis in pseudo mercator (which can lead to distortion errors).
Mar
26
comment How to use QGIS Zonal Stats Plugin from Python Console?
@vinayan the QProgressDialog is useful for visual environments where you want to see how far the calculations have progressed. It has no use from the command line. You can use None as the parameter and it works fine. Then you don't need the from PyQt4.. line or the progressDialog = line. See similar post at gis.stackexchange.com/questions/23203/…
Mar
26
comment How to calculate raster statistics for polygons?
Thanks for your comment, Dan. My answer was missing a necessary import statement, which should now be fixed.
Mar
26
comment Heatmap algorithm to visualise point diversity
Come to think of it, that wouldn't be a problem if you added each new heatmap to the composite heatmap after each category. The question is then which approach would be computationally faster to implement - raster sums or pixel-by-pixel calculation.
Mar
26
comment Heatmap algorithm to visualise point diversity
I have added a visualisation to my question based on this suggestion, and the result looks good! The disadvantage is that if you're dealing with hundreds or thousands of categories, storing all of those rasters is going to be a problem.
Mar
26
comment How to select by polygon in PostGIS with misaligned layers?
Your query finished in 10 min, while my buffer query is still running 11 hours later. I have visually checked the result, and could find no false positives or false negatives. I did find a few areas where the selected polygons extended beyond the biome edge, and these were selected correctly (buffering would not select these). So at least based on my data, this is the way that works!
Mar
25
comment How to select by polygon in PostGIS with misaligned layers?
What a cunning idea! Computationally it's much better, but I imagine it might be prone to false positives? I have a polygon count for your method, but I'm still waiting for my buffer to finish! I'll test more tomorrow.
Mar
20
comment How can I enable Shapefile GUI Loader in pgadmin3?
On my system (ubuntu 12.10), I only had to insert the plugins.ini definition. I think the plugin itself was installed with postgis from the ubuntugis-unstable ppa (see trac.osgeo.org/postgis/wiki/UsersWikiPostGIS20Ubuntu1210). There is therefore no need to install the opengeo version of postgis on more recent versions of Ubuntu, but do use the plugins.ini definition given above.
Mar
14
comment How do I generate a large number of maps?
@Onesime, except for the title and legend, I think you'll be able to adapt the sextante script above to do what you need. You will need to probably remove the selectbylocation step, and add an additional selectbyattribute and saveselectedfeatures step for each season (change grid_layer to all_localities). Then load more .qml files and add append your seasonal shapefiles (top layer appended first). If you're not sure how, I could probably try editing the script above to more-or-less work.
Mar
10
comment QGIS and Ubuntu 'browse' dialogue causing crashing
@mapBaker this does not actually remove qt, only the accessibility addins, which I think are related to screen reading and the like. Apologies for the long delayed reply!
Dec
2
comment How to redefine the nodata value into zero in QGIS?
could you elaborate on how to do that with raster calculator?
Nov
29
comment What to do with -3.4e+38 nodata values?
I'm accepting this answer since it's more likely to work for all input data; if the data is actually in integer format, I'd still go with the other answer.
Nov
29
comment What to do with -3.4e+38 nodata values?
@underdark I couldn't find a ticket that matched this, so I added a bug report (hub.qgis.org/issues/6786).
Nov
29
comment What to do with -3.4e+38 nodata values?
Thanks for your answer, Sylvester. I couldn't get gdal_translate to work using gdal_translate -a_nodata -9999 input.tif output.tif although gdalwarp -dstnodata -9999 input.tif output.tif did the trick. From a 9MB input file, my approach resulted in a 26MB file, whereas gdalwarp resulted in a 52MB output file. However, if the raster contains float values, my approach won't work where this one will.