Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

Archive for January, 2013

Photogrammetry using Bundler, PMVS, GDAL, and PostGIS.

Posted by smathermather on January 8, 2013

Photogrammetric like ortho-photos rendered with GDAL/PostGIS from 3D point clouds created in Bundler and PMVS?  Yes indeedeedoo:

Point cloud in meshlab:

point_cloud

 

And “orthophoto” derived from voronoi polygons in PostGIS, rendered to tif with gdal:

 

Screen shot 2013-01-08 at 10.55.36 PM

 

Hat tip to my3dscanner for making it so easy to generate the point cloud.  More on this later.

Posted in Bundler, GDAL, Photogrammetry, PMVS, PostGIS | Tagged: , , , | Leave a Comment »

Cartographic tricks and tips– making text readable.

Posted by smathermather on January 6, 2013

I was playing recently with techniques for making text/labels in maps more readable in a map.  We can use simple buffers to do this, but this isn’t always adequate.  Take this example:

Labeling

which is a label on top of contours.  It is adequately readable.  If we show 2 ft contours as well, the map becomes somewhat cluttered:

2ft contours

So, we apply the common technique of halo or buffer, which in this case we’ll do in QGIS:

image004

and so we get an adequate result:

image005

If we color the halo the same as our background color, we achieve a subtle but effective result:

image006Overall, I’m pretty pleased with this result. But note the contour lines running through the “O” and “G”, etc.  This would be more readable if we blocked more of the contour linework.  Enter convex polygons:

image007

image008

image010

Overall, I like this effect a lot. It can be subtle but quite powerful.  It would also may a nice addition to existing rendering pipelines as a labeling option, in middleware such as GeoServer, MapServer, or the Mapnik family.

golf_orig ——–>golf_final

Irony here– I’m absolutely awful at anything but mini-golf (putt-putt).

Posted in QGIS | Tagged: , | 4 Comments »