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Hi Ed:<div><br class="webkit-block-placeholder"></div><div>I have had better luck creating DEMs using point data rather than area data. Can you get your RTK to export point data (xyz) rather than the swath segment data. Alternatively, use the "type=point" feature of v.in.ogr. I have never used this feature but the manual says it imports area centroids as points.</div><div><br class="webkit-block-placeholder"></div><div>The next step is to interpret the point data to a DEM raster surface. I have used v.surf.rst to create a raster DEM from irregularly spaced points. It works well. You can use the "maskmap=name" feature to limit the DEM to a restricted area. v.surf.rst expects a raster map for maskmap. You can create one from your field outline shape file with v.to.rst . </div><div><br class="webkit-block-placeholder"></div><div>I can't help on the import problem. Perhaps importing the centroids only with "type=point" will help.</div><div><br class="webkit-block-placeholder"></div><div>I think that precision agriculture is a natural application for Grass. It would be helpful and interesting to hear of your challenges and successes in its use. </div><div><br class="webkit-block-placeholder"></div><div>Regards</div><div><br class="webkit-block-placeholder"></div><div>Dave</div><div><br class="webkit-block-placeholder"></div><div><br class="webkit-block-placeholder"></div><div><br></div><div><div><div>On Jun 29, 2007, at 8:48 PM, Edward Tomlinson wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi,</div> <div> </div> <div>I am also trying to create a DEM from a shapefile.</div> <div> </div> <div>Once again i have some questions about the cell resolution and the interpolation.</div> <div> </div> <div>The use of this is for precision agriculture.</div> <div> </div> <div>The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is about 1 metre (over 1200metres). The shapefile isn't exactly what you would call a contour map. The resulting shapefile is made up of rectangles of equal height. Each rectangle is 8m wide (always as this is the swath width used). The length varies as it keeps ~equal heights together. Technically i suppose this is a contour map, however equal height rectangles are not connected and are not part of the same shape... </div> <div> </div> <div>My other problem is trying to work out what gradient splits should be used. As in i beleive i should use the standard deviation of height as the gradient step value. Does this sound correct??</div> <div> </div> <div>Also i need to restrict the boudary of the DEM to another shapefile. It is just a single shape of the boundary of the field. Mostly all the data is there, however some interpolation will be needed. </div> <div> </div> <div> </div> <div>Currently i am having trouble reading the file in using v.in.ogr.</div> <div>command:</div> <div>v.in.ogr 'dsn=shapefile name' output=elevation09 'layer=Elevation Map 9'</div> <div>Result:</div> <div>GRASS_INFO_WARNING Area size 9e..., area not imported</div> <div>....</div> <div>0 areas imported</div> <div> </div> <div>THere are many columns in the .df file. How can i only import the ones i want? Clearly i have missed something.</div> <div> </div> <div>Any help would be greatly appreciated.</div> <div> </div> <div>THanks,</div> <div>Ed</div> <div><br><br>---------- Forwarded message ----------<br><span class="gmail_quote">From: <b class="gmail_sendername">quinonero juan manuel</b> <<a href="mailto:jumaqu@yahoo.es">jumaqu@yahoo.es</a>><br>Date: 25-Mar-2007 02:45 <br>Subject: [GRASS-user] Creation of a DEM<br>To: <a href="mailto:grassuser@grass.itc.it">grassuser@grass.itc.it</a><br><br> </span></div> <div>1.- You have <span class="st" id="st" name="st">to</span> transform the vector information <span class="st" id="st" name="st">to</span> a rast layer, you can do it using the comand <span class="st" id="st" name="st"> v</span>.<span class="st" id="st" name="st">to</span>.rast, baut before you have <span class="st" id="st" name="st">to</span> determine the cell resolution using for example g.region res=meters</div> <div> </div> <div>2.- If you wsnt <span class="st" id="st" name="st">to</span> create a good DEM you have <span class="st" id="st" name="st">to</span> change the units of the rast layer created, Only have <span class="st" id="st" name="st"> to</span> convert this layer from meter <span class="st" id="st" name="st">to</span> centimeter using r,mapcalc 'cm_layer=rast_meter*100.00'. That's for obtain a good relation betwen horizontal and vertical resolution. </div> <div> </div> <div>3.- Now you have <span class="st" id="st" name="st">to</span> use an interpolatión method <span class="st" id="st" name="st">to</span> create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it'll build faster, dont forget this point!!!!</div> <div> </div> <div>4.- Finally you have <span class="st" id="st" name="st">to</span> transform the results <span class="st" id="st" name="st">to</span> the correct units usin r.mapcalc 'final_DEM=cm_DEM/100.00'</div> <div> </div> <div> </div> <div>If you want <span class="st" id="st" name="st">to</span> generate a DEM usin another interpolation methods please ask!!</div> <div> </div> <div>Sorry for my english</div> <div> </div> <div>Juanma<br><br><b><i>megha shyam <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:capt_lms@yahoo.co.in" target="_blank">capt_lms@yahoo.co.in</a>></i></b> escribió:</div> <blockquote style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><span class="q"> <div>Please help me in creation of DEM.i have a vector layer contaning contour information.How <span class="st" id="st" name="st">to</span> create a DEM model of this.Can you tell me the stpes <span class="st" id="st" name="st"> to</span> be followed</div> <div> </div> <div>shyam</div> <div> </div></span><span class="ad"> <div> <hr size="1"> Here's a new way <span class="st" id="st" name="st">to</span> find what you're looking for - <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://us.rd.yahoo.com/mail/in/yanswers/*http://in.answers.yahoo.com/" target="_blank"> Yahoo! Answers</a> _______________________________________________<br>grassuser mailing list<br><a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:grassuser@grass.itc.it" target="_blank">grassuser@grass.itc.it </a><br><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://grass.itc.it/mailman/listinfo/grassuser" target="_blank">http://grass.itc.it/mailman/listinfo/grassuser</a><br> </div></span></blockquote><span class="ad"> <br><div> <br class="khtml-block-placeholder"></div><hr size="1"> <br><font face="Verdana" size="-2">LLama Gratis a cualquier PC del Mundo.<br>Llamadas a fijos y móviles desde 1 céntimo por minuto.<br><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://us.rd.yahoo.com/mail/es/tagline/messenger/*http://es.voice.yahoo.com/" target="_blank"> http://es.voice.yahoo.com</a></font><div><br class="khtml-block-placeholder"></div><div><br class="khtml-block-placeholder"></div></span><br>_______________________________________________<br>grassuser mailing list<br><a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:grassuser@grass.itc.it">grassuser@grass.itc.it</a> <br><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://grass.itc.it/mailman/listinfo/grassuser" target="_blank">http://grass.itc.it/mailman/listinfo/grassuser</a><br><br><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">grassuser mailing list</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="mailto:grassuser@grass.itc.it">grassuser@grass.itc.it</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="http://grass.itc.it/mailman/listinfo/grassuser">http://grass.itc.it/mailman/listinfo/grassuser</a></div> </blockquote></div><br></div></body></html>