qgis
I want to create a HillShade from a STRM dataset (spatial resolution: 30m) and I realized it has some noise on it (Little squares in the whole image).
I'd like to use Smooth Filters. I presume that QGIS has filters implemented. Could someone explain me how to use it and where I find it?
I suggest to break the process in the following steps.
QGIS Processing Toolbox \ SAGA \ Grid - Gridding \ Inverse distance weighted
http://plugins.qgis.org/plugins/concavehull/
or
QGIS Processing Toolbox \ QGIS geoalgorithms \ Vector geometry tools \ Concave Hull
QGIS Processing Toolbox \ SAGA \ Grid - Gridding \ Shapes to grid
QGIS Processing Toolbox \ SAGA \ Grid - Tools\ Grid masking
With an already created polygon grid, next code works perfectly for my case [to rotate a grid, with 50 features, 70 degrees around QgsPoint(416047.568418, 4443411.85665)]. For particular cases, it's only necessary to change rotation axis and rotation angle.
from math import sin, cos, pi
def rotatePoints(axis, r_angle, points):
points_rot = []
for point in points:
tr = QgsPoint( point.x() - axis.x(), point.y() - axis.y() )
xrot = tr.x()*cos(r_angle*(pi/180)) - tr.y()*sin(r_angle*(pi/180))
yrot = tr.x()*sin(r_angle*(pi/180)) + tr.y()*cos(r_angle*(pi/180))
xnew = xrot + axis.x()
ynew = yrot + axis.y()
points_rot.append(QgsPoint(xnew,ynew))
return points_rot
def createPolygonMemoryLayer(epsg, pol_rot):
uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer""&index=yes"
mem_layer = QgsVectorLayer(uri,
"rotated_grid",
"memory")
QgsMapLayerRegistry.instance().addMapLayer(mem_layer)
prov = mem_layer.dataProvider()
n = len(pol_rot)
#Set geometry
for i in range(n):
feature = QgsFeature()
feature.setGeometry(QgsGeometry.fromPolygon(pol_rot[i]))
#set attributes values
feature.setAttributes([i])
prov.addFeatures([feature])
#Code starts here
layer = iface.activeLayer()
crs = layer.crs()
epsg = crs.postgisSrid()
geom = [ feature.geometry().asPolygon() for feature in layer.getFeatures() ]
points = geom
n = layer.featureCount()
axis = QgsPoint(416047.568418, 4443411.85665)
r_angle = 70
pol_rot = [ [ rotatePoints(axis, r_angle, points[i][0]) ] for i in range(n) ]
createPolygonMemoryLayer(epsg, pol_rot)
After running the code at the Python Console of QGIS, I got:
Best Answer
For Qgis you can use the Orfeo-Toolbox that was initiated by the French Space Agency for remote sensing satellite imgagery. There are lots of options there. You can install it via the osgeo4win installer (when using windows) if you can´t activate it in the processing environment already.
And to the point what to do... Try to read something about remote sensing and filters first, otherwise you will end up with lots of trial and error and you never know if the problem is just not solvable to the level you want(often enough) or you can´t find the right function. If it would be so easy the SRTM would not have the errors...