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Apr
11
comment How to change polygon display/symbol properties in QGIS while digitizing?
try setting the layers' transparency also to 50%
Apr
9
revised How to remove black box around georeferenced grayscale image in QGIS?
added 1 characters in body
Apr
9
answered How to remove black box around georeferenced grayscale image in QGIS?
Feb
19
accepted Missing Georeferencer
Feb
19
comment Missing Georeferencer
Thanks, I was used to see it without activating it in manage and install plugins. Now there is a little glitch, since after I invoke the georeferencer, the georeferencer appears, do not respond for a little moment and I have an error stating "bad allocation". After that i can play with the georeferencer.
Feb
19
asked Missing Georeferencer
Jan
30
comment Step by step LCP Analysis QGIS 2.0
I do not know what version of Qgis you are running. I use 2.01 64 under win 7. R. drain gives me a big blag raster. The path is there but I can not see it. The way I handle the problem was to conver th r.drain raster to vecto with r.to.vect.line. Then the path is visible.
Jan
28
comment Step by step LCP Analysis QGIS 2.0
I run r.cost with the native resolution of your dem and I have no problem, bear in mind that I am using qgis 2.01 64 in win7 with an I7 and 16gb of ram, so it was fast (les than a minute)
Jan
28
comment Step by step LCP Analysis QGIS 2.0
Hello,sorry for the delay, I was able to run rwalk,and rdrain with the model you mentioned. The only thing I changed was the raster resolution. As I understand when you defined your region , the raster resolution is set to 1 (in this case 1 meter). So look for an icon that tells "grass region settings" and change the resolution to something esle more than one. Your dem is 5, so try with 5 or 10. Hope it helps
Jan
28
comment Mapinfo and qgis file's datum problem
The lenght of a degree depends on your latitude check this out:csgnetwork.com/degreelenllavcalc.html
Jan
21
comment Step by step LCP Analysis QGIS 2.0
Try also this: gis.stackexchange.com/questions/77629/…
Jan
21
comment Step by step LCP Analysis QGIS 2.0
You can verify that everything is ok in GRASS by opening a file called wind. This file is located in the Permanet folder of the region you defined. You can open the wind file with a text editor. If it states your zone correctly you are good to perform any operation in your rasters. One trick is instead of using a projected CRS try doing it with a lat-lon CRS. This will force you to reproject all your data but it worked for me
Jan
21
comment Step by step LCP Analysis QGIS 2.0
You can try this. First prepare all the basic layers in Qgis. Slope, rasters from vectors. Define step by step as directed in the tutorial I mentioned, the region and the map set using the GRASS ui, not the qgis one. Then do the import the rasters (slope, dems, rasterized vectors). Reclasify what you need. Export to geotif. Go back to qgis and perform the union with qgis raster calculator. This will give you the friction surface you need for rwalk or r.cost. Now using grass under qgis import your friction surface and try to run r.cost or r.walk and r. drain. Sounds cumbersome but it worked
Jan
19
comment Step by step LCP Analysis QGIS 2.0
I experienced tha same problem as you with a grass region defined in QGIS. I solved the problem by using the GRASS UI (included in your qgis installation) and following this tutorial ing.unitn.it/~grass/docs/tutorial_64_en/htdocs/esercitazione/…. Once defined correctly the region I was able to use UTM data without problems
Jan
19
comment Step by step LCP Analysis QGIS 2.0
Why use the raster calculator?Suppouse you are giving the slopes 75% of weight and the rivers 25%. Both layers can create a new raster with their sum (for instance) showing your friction surface.
Jan
19
comment Step by step LCP Analysis QGIS 2.0
Try to set correctly the null valu for the rariver raster, I did an experiment get the blackbox you mention, but noticed that there were many pixels wiyh 0 value, so I defined that the null value should be 0 and my rivers appear. I did all the process in Qgis, Convert the raster an define the null value in the layer properties. To make definitive the null value you can use raster/conversion/translate to define the river raster with the correct null values
Jan
17
comment Is there a bug in Georeferencing in QGIS 2.0?
Look at this. It may help: gis.stackexchange.com/questions/72190/…
Jan
17
comment Step by step LCP Analysis QGIS 2.0
For the union, you can not make the operation using a line and a polygon. In the tutorial I mentioned before the layers that the author used both are polygons. In this sense the union must use layers of the same geometry type. Can You post an Image showing Why the rivers look wrong after line to polygon function?. What I usually do is convert my vector layers to raster and the perform the union using the raster calculator.
Jan
17
comment Step by step LCP Analysis QGIS 2.0
Try to calculate the slopes in qgis qith the merged file. To do this go to raster/Analysis/DEM (terrain models). In the dialog box set the mode option to slope. Choose either degrees or percent. Then,there is an option that says "scale (ratio of vert. units to horiz). This is where you define the scale factor I mentioned before. Once Qgis calculates the slopes you can import the slope raster in GRASS.
Jan
16
comment Step by step LCP Analysis QGIS 2.0
For the second you can try to merge the dems in one raster (raster/miscellaneous/merge). Then try to calculate the slope. One thing, if your dem is in a lat-lon CRS you must define a scale (ratio of horizontal to vertical units) factor to make the calculations, in this case 111120. For data sets where the horizontal and vertical measuring units are the same (like UTM)the scale factor is 1.