<div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div>
> Seriously though (& not arguing :-)), "a semi-trailer truck poking out of a<br>
> roof. Pavement staining and tire marks from fork lifts" wouldn't really be<br>
> enough to say definitely whether you're looking at a roof over an open area<br>
> or an enclosed building, would it? That truck could be poked out of the<br>
> doors of an enclosed loading dock, & the forklift could be doing the same?
</div><div><br></div><div>Usually, no single thing will lead to a conclusion. The identification 'keys'</div><div>basically indicate the other things depending on the context one should <br></div><div>look for. Hey, it could be a short truck, too :-) Preponderance of evidence.</div><div>Which is why it's useful to use multiple imagery sources.</div><div> <br></div><div>Bing and Google Maps are aggregators of imagery - they license it from</div><div>other companies, at some price, at various resolutions, and what shows</div><div>can change over time - urban areas get updated very frequently, not so</div><div>much when you get out into the sticks. Even this isn't an absolute, by some <br></div><div>freak of availability we observed a bear on the road of my brother's</div><div>property on the Front Range in Montana. Also, the orthorectification</div><div>can sometimes be crap ( adjusting for terrain, etc. )<br></div><div><br></div><div>
> Yes, if you've got slanting or night time imagery that may help, but I've<br>
> never seen it in the areas I map in :-(>
</div><div><br></div><div>You can add your own sources to JOSM, the presets are the more or</div><div>less globally useful services. Sometimes, you don't need to actually</div><div>add it to JOSM to assist, like the building overhang issue. Our <br></div><div>county has phenomenal lidar point data available ( 6"), I can make out</div><div>the location of the picket fence on my front lawn. Our state flies</div><div>regular oblique photography to monitor coastal conditions, also. <br></div><div>There is an upfront effort of finding what's available, but once you</div><div>have the endpoints and sources for your area of interest, it can</div><div>make things easier. <br></div><div><br></div><div>For instance:<br></div><div>JOSM displaying the USGS 3DEP ( derived from Lidar surveys ) <a href="http://bit.ly/2Rjb8LO">http://bit.ly/2Rjb8LO</a></div><div>- in some areas it has 1 meter resolution along with slope aspect, etc.</div><div> <a href="https://www.usgs.gov/news/new-elevation-map-service-available-usgs-3d-elevation-program">https://www.usgs.gov/news/new-elevation-map-service-available-usgs-3d-elevation-program</a><br></div><div>and for thermal ASTER (
Advanced Spaceborne Thermal Emission and Reflection Radiometer) <br></div><div><a href="https://bit.ly/2FoslNE" target="_blank">https://bit.ly/2FoslNE</a> - not great, it's a fairly old platform and varies between 15 to 90 square <br></div><div>meters per pixel, but I had it handy.</div><div><br></div><div>> On the subject of clarity of images. Was mapping the other day (using iD),<br>
> marking buildings in an industrial area. As I said, the photo's weren't the<br>
> clearest, but I was also peering through the purple haze of the mapped<br>
> area=industrial, which certainly doesn't help matters either :-(
<br></div><div><br></div><div>Yeah, we have
308 cloudy days a year. Which underscores the value of</div><div>having sources that have multiple times available. Leaf on and leaf off</div><div>is also useful. If Bing's blender picked a day when an inversion layer</div><div>was occurring, it's nice to pick another day. Night imagery is rare. <br></div><div><br></div><div>The gold standard for this is SAR ( synthetic aperture radar ) <br></div><div><a href="https://earth.esa.int/web/eoportal/satellite-missions/t/tsx-ng">https://earth.esa.int/web/eoportal/satellite-missions/t/tsx-ng</a></div><div>but it isn't really mainstream yet, may never be for the general</div><div>public for obvious military reasons. Many countries are launching these</div><div>platforms, though, so it may be like the 'fuzz' on GPS accuracy, <br></div><div>
<div>once everybody has it, they'll open it up.</div><div><br></div><div>Depending on your level of commitment, it's useful to have some</div><div>minimal skill with QGIS, just for these discernment purposes. Then <br></div><div>you can do things like pansharpening ( <a href="https://www.geoimage.com.au/images/services/pan_sharp_bne_qb.jpg">https://www.geoimage.com.au/images/services/pan_sharp_bne_qb.jpg</a> ), contrast adjustment, etc. very simply just</div><div>by altering the layer transparency - tasks that aren't possible in JOSM. <br></div><div><br></div><div></div><div>Michael Patrick</div><div>Data Ferret<br></div>
</div><div><br></div><div><br></div></div></div></div></div></div></div></div></div>