<html><body><div style="color:#000; background-color:#fff; font-family:tahoma, new york, times, serif;font-size:10pt"><div><span>Hi Margherita,</span></div><div><br><span></span></div><div><span>Grazie. Its not related to hydrology. I just want to get some shape indexes to characterize networks of polygons (periglacial patterned ground).<br></span></div><div><span></span><span>I came to your Grass Add-on because the indexes used in 2D basin morphometry are really adequate to characterize each individual polygon.<br></span></div><div><span><br></span></div><div><span>I have already used SAGA GIS and GVSig, which automatically supply shape parameters relating the perimeter of the polygon to its area in various ways. And thatīs already fine information. <br></span></div><div><span>From that I know if the polygon is more elongated or more circular. And maybe more information wonīt add to much... But I still would like to try. Mainly because of the indexes
which grab the axis and which relate the polygon to and ideal shape. </span></div><div><br><span></span></div><div><span>Maybe I should focus on doing one thing at a time: 1) axis calculation; and 2) deriving the ideal shape from the centroid of the polygon.</span><span> Then Iīd have great information. <br></span></div><div><span><br></span></div><div><span>My next step is to go inside you python code (of which I know little) and try to extract the relevant pieces. </span></div><div><br><span></span></div><div><span>Thank you.</span></div><div><span>Marco<br></span></div><div><span>(gonna start a MSc <font size="2"><font face="Arial">related to cryosphere geomorphology next Fall)</font></font><br></span></div><div><span><br></span></div><div><span></span></div><div><br></div> <div style="font-family: tahoma, new york, times, serif; font-size: 10pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;">
<div dir="ltr"> <font face="Arial" size="2"> <hr size="1"> <b><span style="font-weight:bold;">From:</span></b> Margherita Di Leo <diregola@gmail.com><br> <b><span style="font-weight: bold;">To:</span></b> Marco Jorge <marco_gjv@ymail.com> <br><b><span style="font-weight: bold;">Cc:</span></b> "grass-user@lists.osgeo.org" <grass-user@lists.osgeo.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Thursday, June 7, 2012 11:26 AM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [GRASS-user] r.basin ? for plane geometry of polygon shapefiles<br> </font> </div> <br>
<meta http-equiv="x-dns-prefetch-control" content="off"><div id="yiv260400510">Hi Marco,<br><br><div class="yiv260400510gmail_quote">On Tue, Jun 5, 2012 at 4:54 PM, Marco Jorge <span dir="ltr"><<a rel="nofollow" ymailto="mailto:marco_gjv@ymail.com" target="_blank" href="mailto:marco_gjv@ymail.com">marco_gjv@ymail.com</a>></span> wrote:<br><blockquote class="yiv260400510gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div><div style="font-size:10pt;font-family:tahoma, new york, times, serif;"><div>Hi,</div><div><br></div><div>I have 10k small polygons stored in a shapefile and in raster format (nr classes = nr of basins). </div><div>I am interested in getting some planar geometry information for each polygon.</div>
</div></div></blockquote><blockquote class="yiv260400510gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div><div style="font-size:10pt;font-family:tahoma, new york, times, serif;"><div>I have 3 problems, not considering the lack of knowledge: </div>
<div><br></div><div>- no DTM; </div><div>- no channels; </div><div>- try to foul r.basin with the shapefile</div><div><br></div><div><span style="font-size:10pt;">Can you think of a way to pick the module and its code to calculate the indices in the end of the post? </span></div>
<div><span style="font-size:10pt;">Can anyone point me a way to pick up the major axis instead of the lenght of the main channel ? </span></div><div><span style="font-size:10pt;">Any hint on major (or minor) axis
extraction?</span></div><div><br></div><div>Should I try other approach? </div></div></div></blockquote><div><br></div><div>To me, it's not clear what you are trying to get. If your aim is to perform a hydrological analysis, you do need a DEM, and you can easily download i.e. an ASTER GDEM for your area and then use r.basin. If your analysis it's not related to hydrology, and you just need some "shape indexes", what you should do is probably related to what you are trying to achieve.. Can you explain a little more?</div>
<div><br></div><div>Regards,</div><div>madi</div><div><br></div><div><br></div></div>-- <br>Dr. Margherita Di Leo<br>
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