Dear TerraServer Gurus, I'm having trouble with my Google Maps/TerraServer "mash-up" where the latitude and longitudes passed to TerraServer do not seem to be converted to UTM coordinates with sufficient precision (off by approximately 100 meters).
I'm using a method several other Google Maps API users have described (e.g., http://tinyurl.com/yzvl6gr) to integrate TerraServer's DRG tiles as an option (map type) within a map displayed by Google Maps. Among other things, this method passes &REQUEST=GetMap and &SRS=EPSG: 4326 to http://www.terraserver-usa.com/ogcmap6.ashx. Although the resulting TerraServer DRG map type (TOPO) displays the USGS DRG image and responds to the Google Maps scale controls, points displayed on TOPO appear to be approximately 100 meters south and 50 meters east of where they appear on the Google Maps types (e.g., Terrain). For example, here's a test page from my web site that attempts to display a map approximately centered on the summit of Mt. Whitney in California (with a marker on this location), which (according to http://tinyurl.com/ykd8edj) is at longitude, latitude (-118.2934244, 36.5782684): http://www.vulgarianramblers.org/whitney_test.php If you increase the magnification and then compare the location of the marker in "TOPO" mode vs. that in "Terrain" mode, you'll notice that the former is approximately 100 meters SSW of the true summit. More importantly for my application, the TOPO location is approximately 100 meters SE of the Terrain location. I wanted to test the TerraServer EPSG:4326 projection support outside my application, but unfortunately latitude and longitude coordinates entered directly into the web interface at http://terraserver-usa.com are apparently "gridded" to nearby locations. For example, when I enter (-118.2921002, 36.57871135) into the Longitude and Latitude boxes on this page, the GO button displays a map that is centered on (-118.27879, 36.59925) instead, at least according to the values now displayed in those boxes. As I change the resolution of the map, the coordinates displayed in the boxes change again (as does the location appearing in the center of the map). This is apparently due to the tiling of the source data, but it effectively prevents me from testing coordinates to a resolution within 100 meters. I am aware of the inherent difference between the projection & datum used for NAD27 UTM coordinates vs. those for WGS84 latitude/longitude pairs. I also understand that the USGS DRG tiles provided by TerraServer originate from USGS maps using UTM projections. I would prefer to pass UTM coordinates to TerraServer (so that it didn't have to take the time to convert from EPSG:4326), but the Google Maps mash- up apparently requires me to use EPSG:4326 latitude and longitudes. Any help would be greatly appreciated. Thanks, - Chris --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/google-maps-api?hl=en -~----------~----~----~----~------~----~------~--~---
