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17

Most methods to spline sequences of numbers will spline polygons. The trick is to make the splines "close up" smoothly at the endpoints. To do this, "wrap" the vertices around the ends. Then spline the x- and y-coordinates separately. Here is a working example in R. It uses the default cubic spline procedure available in the basic statistics package. ...


12

In principle, you cannot do this in a unique, accurate way without reconstructing something like the original DEM. Let's see why, by doing the computation with a (difficult but realistic) example. It begins with a small portion of a 30 meter DEM, about 15 by 11 kilometers. Contours have been computed at regular intervals: this is where you begin. To ...


10

Cartographic rules to represent the relief as contours are presented in Imhof's famous book on relief representation, chapter C. Some of these rules are given on this wikipedia page. The main recommendation when simplifying contours it to preserve the terrain main characteristics. Smoothing the contours independently do not prevent them to overlap: It is ...


10

Assuming you have Spatial Analyst license: Interpolation: Spatial Analyst Tools -> Interpolation -> IDW ('Z value field' parameter will be your 'P' field). Reclassification of interpolated surface into 3 zones: Spatial Analyst Tools -> Reclass -> Reclassify Specify interpolated surface and ranges of desired classes: 0 - 5,... Now you have a raster which ...


10

If you are looking to convert DEMs to contour lines: QGIS Plugin Contours For converting scanned topo maps to vector contour lines, Arcscan is one of the easiest (and most sophisticated) programs out there. However, there are several opensource alternatives, including a promising GRASS approach: Trace vector contours from a scanned map. Additional ...


9

The answer depends on context: if you will be investigating only a small (bounded) number of segments, you might be able to afford a computationally expensive solution. However, it seems likely that you will want to incorporate this calculation within some kind of search for good label points. If so, it is of great advantage to have a solution that either ...


8

Here we go then, a method to get some control over contour label placement, see the picture. The first thing I did was to load the contours. Next, on a new line shapefile, I drew a line from the top of the hill to the bottom (the labels in the picture are aligned with this). I then buffered the line and used the buffer to clip the contour layer. After that ...


8

Evaluation of the options Contour lines represent continuous surfaces, so their comparison ultimately is a proxy for comparing those surfaces. Because both the surface values (elevations) and locations are potentially subject to error, there are two components to the comparison: in terms of value and in terms of position. The two cannot be separated, ...


8

You can download raw contours lines from the National Map Viewer. I like to download by bounding box (button highlighted in red).


7

After using v.surf.rst, it's only a question about how to display the resulting cost raster. GRASS offers r.colors to specify a color map for a raster. As far as I can see, the normal behavior of GRASS is to interpolate colors, so you you'll have to work around this: r.colors map=travel_costs color=rules 0 green 100 green 101 yellow 200 yellow 201 red ...


7

I would highly recommend going through the Contour lines to DEM tutorial, available from GRASS wiki. Essentially, they describe different interpolation methods used to produce a DEM. Avoid IDW interpolation using contour lines (i.e. described in one segment of the tutorial) since this is an inappropriate use of the interpolation method. The GRASS module ...


6

GRASS has also many options http://grass.osgeo.org/wiki/Contour_lines_to_DEM available one way or another also trough the QGIS/GRASS plugin.


6

Yes, there are several options available in QGIS: Inverse Distance Weighting (IDW) Interpolation plugin - see this for a tutorial GDAL Raster plugin - to access, click Raster > Grid (Interpolation). GDAL's interpolation is more robust because you can use other interpolation algorithms (IDW, nearest neighbor, moving average, etc.). This tools only ...


6

I would say this depends on your knowledge of the data and how it was collected as well as how the DTM was generated from the raw data (regular grid vs interpolated from irregular points or other sources) I don't think there is a rule of thumb. Personally, I choose contour intervals based on the scale, type, content, purpose of the map, etc.


6

The Raster|Extraction|Clipper tool will help you to do this. You can open the tool and then click and drag in the raster image to select the area you want to export as a new raster (Clipping mode: Extent), and then refine the exact coordinates in the Extent fields (if necessary). Probably no way to do contours on only a selection of a raster; clip it this ...


6

In the GRASS GIS Wiki, there is a dedicated page for this: http://grass.osgeo.org/wiki/Contour_lines_to_DEM The page demonstrates and compares a number of different methods of converting vector contour lines into raster DEM surfaces including screenshots.


5

For many contour maps a check of spatial consistency among the contour levels is not possible unless you supply additional information. Here's an example pulled arbitrarily from Google Images: The criterion for consistency is that the neighboring lines of each contour line should have values differing by at most one contour interval. But if you draw a ...


5

You first need to make a raster DEM from your contours. That requires the Spatial Analyst extension, and uses the Topo to Raster tool (Spatial Analyst | Interpolation toolbox). That elevation raster can then be used as the input for the Slope tool. Note that since this is an interpolation process, it is estimating the elevation values between the contour ...


4

You first need to create a raster layer from your vector contour layer. You can use the Topo to Raster tool under the Spatial Analysis Tools>Interpolation toolbox (reference via vs 9.3.1 not sure if it is the same in 10). Once you have your raster layer, then you can use the Hillshade tool.


4

If you use the regular placement in maplex there are options to offset. With this result... You can set the offset units to points, mm, or mapunits. There is not a specific ladder constraint but as you notice these did ladder fairly nicely. I have seen that it is hit or miss though with out the constraint.


4

In the Symbology tab you can classify your own values and apply to the contours http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?tocVisable=0&ID=-1&TopicName=contours&pid=1


4

Also according to my experience Aster-generated dems are noisy. I usually try to run a low pass filter to smooth the data from the command line window. Anyway, I don't think you will be ever able to obtain good 1m contour lines from Aster (noise, pixel size of 30m, low precision ecc ecc)! I guess you need another source...


4

What do you mean by 'generate contours'? Do you have contours as shapefiles and want to display for the selected area only. That can be achieved using OpenLayers CQL filters. If this is not the case, what elevation data do you have? In case you are using DEM, you can check this link : Developers Corner: have your SLD transform raster data into vectors on the ...


4

Giving you GRASS and GDAL based answer if that's an option for you. GRASS - r.surf.contour is the tool meant to interpolate contours to create DEM. http://grass.osgeo.org/wiki/Contour_lines_to_DEM#r.surf.contour If using GDAL is an option, try this. ( Install OSGeo4W and run following from shell ). This is an easier option, but kind of a hack, so use with ...


4

I think you need to Convert Labels To Annotation. Once they are annotations (which are like "graphics" for labels) you can select and delete any you want within an edit session.


4

This is elevation data from the OS OpenData dataset? If you want to extract contours it's probably best to use the ASCII (*.asc) rasters. You can load these and then extract the contours by going Raster -> Extraction -> Contour. You might find it convenient to make a virtual raster (VRT) file from your nine tiles before you try extracting the contours: ...


4

If you have a contour value field, it should be possible to select **50m and **00m contours for later deletion using the following query with the modulo operator: value % 50 = 0


4

I use the "Buffer" option on the "Label setting" tab. (Using the labels button, not the old labels option on the layer properties dialog.) This does not wipe out the contour line, as I imagine you are wanting to do, but it does make the label legible.


4

I managed to do this by making a new field in my shapefile called 'ELEVATION'. You can add fields in ArcCatalog. I copied the data over to the new 'ELEVATION' field, so the two were identical. When I exported to CAD, CAD picked up the data seamlessly.


4

This ESRI blog post describes a method for finding depressions using contours. On a topo map depressions look like this: Note that the above approach is not desgined to be programmatic, but simply relies on symbolizing the contour lines using different colors so that you can visually find lines which do not fit the pattern of stepwise increases.



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