Hello again: Perhaps there is an incompatibility between QGIS and GRASS: now QGIS produces "-inf" (-infinite) values for null cells, so any operation or function that involves al least one those cells, give us -infinite values (constant + - * / -infinite = - infinite).
So, as you get -inf values, then scale of values is so large that finally all is pink color. I think that it must be fixed to get "null" values again, as in QGIS 1.8 version, because GRASS works with "null" values, not with -inf... or What do you say, dear developers?. Regards Carlos Cerdán 2014-07-14 16:23 GMT-05:00 Ivan Santiago <[email protected]>: > Hello all: > > Thanks to Carlos Cerdan for his advice. Apparently, QGIS has some issues > with integer rasters containing nodata values. When the raster for masking > use is floating point, QGIS does not paint nodata cells. On the contrary, > when the original raster is integer, QGIS fills nodata cells with pink > color (which makes no sense). The big problem/question is why even if the > mask exists, further rasters will not have nodata values outside the AOI. > > Then... > Following Carlos' advice, I converted nodata cells to zero using r.null.to > Since my purpose is to compute area coverage and percent coverage for risk > zones inside a municipality: > I multiplied the 1,0 raster layer by the integer risk_index (that is 1to5) > > Then I used r.null.val to set zero value cells to nodata because I wanted > to use r.stats to compute areas and percentages with the option of ignoring > nodata cells. > > Finally (and happily) the r.stats results were more realistic, taking away > the area outside the "mask". > > --------------------------- > Iván Santiago > GIS Specialist > Information Technologies > Office of Management and Budget > 787.725.9420 x 2378 > Calle Cruz 254 > PO Box 9023228 > San Juan, PR 00902-3228 > http://gis.pr.gov > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user >
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