My DEM raster coordinates are in WGS84: 45.4763884,-121.5736061 and vertical units are in feet I believe. I want to do a slope analysis.  Do I need to add scale factor?  I have been seeing different answers all over and am confused.
110277
After the DEM creation, I wanted to create slope layer.   However, the result has not satisfied me. I don't think the slope map is correct. Have you ever encountered false calculated terrain map?  This is the DEM:    And this is the slope layer.
69896
What strategies, criteria, or rules do you use for selecting coordinate systems for    (a) storing,  (b) analyzing, and  (c) displaying GIS data?     (I humbly offer  to a  about watershed analysis as an example of the considerations involved in (b).)  What are the pitfalls to watch out for?  Links to Web sites you find particularly helpful in this regard are welcome.
42273
I need to classify tree heights in a DSM of a slope-y terrain. It´s not a forest but several individual / detached trees. In a plane terrain it won´t be an issue but in that uneven terrain I need somehow to extract the height of the single trees as related to the surrounding ground.   Is there any way to do so using QGIS?   The DSM file is a Tiff, but I can also get it as a point model if this helps.
20803
I'm working with QGIS, v. 2.0.1. I have several soil types. They are (amongst others) described with slope indications. I already calculated the slope from the DTM in degrees, but as description of the soil types is in percentage, I need to calculate the slope in percentage. I tried two things:  I tried the analysis tool from the raster section, but it didn't work. The result was just black with values from 0 to 0. The same happened when I tried to calculate the percentage in the raster calculator but the result was the same.  Maybe I need to say that the terrain is pretty plain. What else can I do? Update I tried the raster calculator and did what @radouxju suggested. It gave me a black picture with values from 1756.64 to 1756.64. But as soon as I click in the picture the values are &quot;normal&quot;, say 5.88 or 13.224 or something like that. The same happens when I try the gdaldem tool but with values from 0 to 0. I also tried to change the contrast enhancement (like stretch to min/max) but it didn't change anything. Update 2 I just  that maybe I have to set the scale to 111120  but that doesn't work neither (result: black, values 0-0).
104720
I am using the scale bar of the QGIS composer (ver 1.8) and I don't understand how the whole thing works.    Where can I set the units properly? The layers have idential CRS (WGS84), the settings for map tools is in meters.  I have tried to get it correctly by changing segment size and map units per bar unit, but it doesn't work. However, I have to admit that I don't understand what these two fields actually mean.
103224
I am creating a python script to generate a terrain. In the process I am creating two feature datasets. However, in order to successfully create this FD, i need both horizontal and vertical datums. I am able to code the horizontal datum successfully, but unable to input the vertical datum. Although the code does not error out, it does not create the requested feature dataset. I used the ESRI WKID's to reference horizontal and vertical datum as shown below.  Here is the code line for spatial reference that I used:  sr = arcpy.SpatialReference(horizontal_wkid)   I tried doing this sr = arcpy.SpatialReference(horizontal_wkid,vertical_wkid) but to no avail.  I am using ESRI ArcGIS 10.2 and coding in Python 2.7
11680
My question is about extracting values from rasters at the location of points. With the function extract this is very easy, and the function gives me a dataframe with the values of all the variables in the points. I want to have in that dataframe the coordinates of each point. How can I make that happen? Is it possible to say to R that when extracting the values from the raster also add the columns of the location point.  This is my procedure:  presencias=read.table("c:/SDM_R/presencias/P_lentiscus_pres.csv",header=TRUE,sep=";")  lista_variables &lt;-list.files(path="Variables_modelizacion/solo_ascii",pattern='*.asc',full.names=TRUE) variables &lt;- stack(lista_variables)  variables_presencia&lt;-extract(variables, presencias)   the results are something like these:  &gt; bio1  bio12  bio18  bio2  bio4  &gt; 90    875    165    95    4886 &gt; 115   1085   158    83    4075 &gt; 135   1153   153    67    3402 &gt; 85    1026   137    99    5203 &gt; 96    667    128    108   5823 &gt; 98    531    109    113   6305 &gt; 132   450    63     123   6598 &gt; 132   569    104    106   5963 &gt; 95    814    196    98    5571 &gt; 146   474    39     114   6603   But I want two more columns with the coordinate data (but could be others columns from my csv extracting location table).  Thank so much.
109636
I have a DEM raster with pixel values between about 3000 and -0.0003. I need to set all pixel with a value of 0 and smaler (&lt;=0) to "nodata" (for later raster calculations and to reduce the filesize).  It seems for me that this is a task for the raster calculator (set value of  pixels &lt;=0 to "nodata") or a reclassification (set value of  pixels &lt;=0 to "nodata" and keep all other values) but I dont know how.
122551
I have a list of surveyor points, and I will need to create a DEM model out of it ( in geotiff format if possible for space consideration, if not, then in ASCII grid format).  I need the DEM for watershed and catchment delineation purpose.   Instead of using existing software like ArcGIS, I want to write my code to do it ( in C++ or C#), so that I can later integrate them into my own GIS software. is there anything in GDAL or other open source tools that do this well? Or do I have to write from scratch?
10645
I'm attempting a simple slope analysis in QGIS2 using the plugin at Raster -> Terrain Analysis -> Slope. The slope output layer has a very strange histogram, basically spikes at 0 and at 89.9098 with one big valley in the middle:    Here's the initial DEM:    And the resulting slope layer (note that Contrast Enhancement is already at 'stretch to minmax'):    The place I got the DEM is the NED. I tried the gridfloat format, and the arcgrid format, and the IMG format. I downloaded from nationalmap and also from atlas.ca.gov - all seem to have the same resulting histogram.  The procedure I used to make the slope layer was Raster -> Terrain Analysis -> Slope, GeoTIFF, Z factor = 1.0 (what does that do anyway?)  Seems like simple pilot error; however: I found  online (for QGIS 1.something) that comes with a sample DEM, and it worked just fine using the same procedure. So, it's not a fundamental QGIS2 bug.  So, it must be slightly more complex pilot error: there must be a conversion step or something I'm missing?
109579
I'm trying to analyse a a 3 x 3 metres scan derived from terrestrial photogrammetry (i.e. local coordinates, with 0,0 in the centre of the point cloud) to obtain a DSM.  Importing the file in lidR, I get the following warnings:  Warning messages: 1: Invalid header: X scale factors should be factor ten of 0.1 or 0.5 or 0.25 not 2.23339664936066e-09  2: Invalid header: Y scale factors should be factor ten of 0.1 or 0.5 or 0.25 not 2.33016455173492e-09  3: Invalid header: Z scale factors should be factor ten of 0.1 or 0.5 or 0.25 not 4.71837997436523e-10    I specified the scale to 0.001 using lasrescale (suggested  too).  Then, I tried using lasreoffset to shift the point cloud to the correct geographical coordinates ( a similar implementation using LAStools), but I get this error:  las = lasreoffset(las, xoffset = 1306977.096, yoffset = 5661354.023, zoffset=265.8018) #&gt; Error: Incorrect xoffset: integer overflow.   When manually adding the offset to each point (e.g. las@data$X + 1306977.096, etc), the procedure works.  Finally, once I try to rasterize the point cloud using:  r = grid_canopy(las, res=0.01, dsmtin())   I get another error:  Error: Internal error in C_interpolate_delaunay: xy coordinates were not converted to integer. Scale factors are likely to be invalid.   It looks like I'm using the wrong tools for the purpose, or totally missing the point. Any suggestions?  Furthermore, can anybody help me understanding what does "integer overflow" refer to in this case?
60539
I wanted to create a DEM of constant slope say 1/3000.   How can I proceed in ArcGIS Desktop 9.3?   The area may be 1000m x 1000m or any other as per convenience.
21536
I have a raster with float number values for example: 2.544459104537964 and I want to round these up to integers. I have seen other posts on ArcGIS like  but when I use Raster Calculator in QGIS, Int(myraster + 0.5) only makes the first value (which is 0) to 0,5 and the last one (which is 100) to 100,5. The other pixels stay float.
42279
I have two rasters: a digital elevation model (DEM) and a Landsat band. The grid resolution of both is 30 m, but the grids are not coincident (see image: the dark raster on top is the DEM; the light raster underneath is the Landsat band).  I want to perform some transformation of the Landsat band so that its grid aligns perfectly with the DEM grid. I've tried resampling the Landsat band to 30 m in ArcGIS using the DEM as a Snap Raster in the Environment settings, but this does not have any effect. I've also tried clipping the Landsat band to the extent of a vector polygon (that the DEM is also clipped to), while setting the DEM as the Snap Raster, but to no avail.  I suspect this is happening because both rasters are already at the same resolution (just on different grids), but I really need their grids to be aligned to be able to do any further analysis.  Can I do this in ArcGIS Desktop?
61809
Does anyone have a simple work-flow for drawing cross sections of earth features in QGIS?   My thing is that QGIS is being used to present the plan view, but we have a little interest in some elevations as well. All the data is one set and is simply an elevation value in the attribute table, I don't want to have to move all that to CAD.  One logical workaround is to present the z value as the y.  I am a dunce in paper space in CAD, and would be more comfortable with the QGIS Composer.
81996
Trying to load and plot a raster (it's a DEM) in R, but having problems.    Using R I read in a raster file:  library(raster)  dem &lt;- raster("DEM_Victoria.tif")  # &gt;70 MB print(dem)  class       : RasterLayer  band        : 1  (of  3  bands) dimensions  : 5444, 6007, 32702108  (nrow, ncol, ncell) resolution  : 100, 100  (x, y) extent      : 176615.6, 777315.6, 5650397, 6194797  (xmin, xmax, ymin, ymax) coord. ref. : +proj=longlat +ellps=WGS84 +no_defs  data source : DEM_Victoria.tif names       : DEM_Victoria values      : 0, 255  (min, max)   My confusion here is the extent vs the CRS. The extent shows coordinates from a UTM Zone 55S system, while the CRS reports it as longlat.   Similarly, gdalinfo reports:  Driver: GTiff/GeoTIFF Files:  DEM_Victoria.tif Size is 6007, 5444 Coordinate System is: GEOGCS["GDA94",     DATUM["unknown",         SPHEROID["unretrievable - using WGS84",6378137,298.257223563]],     PRIMEM["Greenwich",0],     UNIT["degree",0.0174532925199433]] Origin = (176615.587999997427687,6194797.138000000268221) Pixel Size = (100.000000000000000,-100.000000000000000) Metadata:   AREA_OR_POINT=Area Image Structure Metadata:   COMPRESSION=LZW   INTERLEAVE=BAND Corner Coordinates: Upper Left  (  176615.588, 6194797.138) (Invalid angle,Invalid angle) Lower Left  (  176615.588, 5650397.138) (Invalid angle,Invalid angle) Upper Right (  777315.588, 6194797.138) (Invalid angle,Invalid angle) Lower Right (  777315.588, 5650397.138) (Invalid angle,Invalid angle) Center      (  476965.588, 5922597.138) (Invalid angle,Invalid angle) Band 1 Block=6007x1 Type=Byte, ColorInterp=Red Band 2 Block=6007x1 Type=Byte, ColorInterp=Green Band 3 Block=6007x1 Type=Byte, ColorInterp=Blue   Is this real? A problem? (well it is to me, but perhaps because I don't understand something) Fixable?  I tried 'Assign projection' in QGIS, which uses this command:  gdalwarp -t_srs EPSG:28355 -srcnodata -32768  DEM_Victoria.tif DEM_Victoria.tif.tmp   but it failed with:     ERROR 1: Too many points (12100 out of 12100) failed to transform,   unable to compute output bounds.
60528
I have made a raster elevation map of Greenland, and have information of the region, cities and more as vectors. The information is not in the same place as my elevation map.  I have selected EPSG:5938 on the bottom right in QGIS and on my informations and elevation map I have set the CRS to the same like the picture    How do I get it all on the same position?