Re: [Qgis-user] How do I register a Google Map?

[Randal Hale]

Oh man you are about to have fun. My apologies to the list if this gets too weird and wild. 1. You downloaded a ZIP file from the data gateway - I'm going to use an example from my neck of the woods in TN. That zip file contains a file that is going to look similiar to ortho_1-1_1n_s_TN135_2012_1.shp.txt. It is a text file and if you scroll through it it describes all the fun that was had in the making of this image. The coordinates will be in UTM (your GPS points are WGS84). About halfway down you will see a block of text in this file that looks like: Spatial_Reference_Information:   Horizontal_Coordinate_System_Definition:     Planar:       Grid_Coordinate_System:         Grid_Coordinate_System_Name: Universal Transverse Mercator         Universal_Transverse_Mercator:           UTM_Zone_Number: 16           Transverse_Mercator:             Scale_Factor_at_Central_Meridian: 0.999600             Longitude_of_Central_Meridian: -87.0             Latitude_of_Projection_Origin: 0.0             False_Easting: 500000             False_Northing: 0.0 This means that the file is in UTM Zone 16 NAD 83. I'm going to guess you are zone 15 or 14 2. Start a new project and add the NAIP image. 3. Georeference against the NAIP (ignoring your GPS points) for a bit. You want to use the same coordinate that the SID is in for simplicity. 4. Once it is georeferenced doubel check your new rectified file against the SID - see if they line up. If YES.... 5. Add your GPS - QGIS shrould re-project on the fly and move them to the right spot. If all of this gets too crazy - email me off list and I can walk you through it and we can summarize for everyone following along. Randy ----------------- Randal Hale, GISP North River Geographic Systems, Inc http://www.northrivergeographic.com 423.653.3611 rjh...@northrivergeographic.com <mailto:rjh...@northrivergeographic.com> twitter:rjhale http://about.me/rjhale On 02/05/2014 02:32 PM, Mike Keelan wrote: OK I already have a .sid file for the area of interest, but if im going to use the coordinants as given from the Qgis program the data does not seem to be compatable with the GCP table info, or the Infor requested in the input dialog box to create the reference points for the .jpg raster.  ie the format from the Qgis main view is xxxxxxxx,xxxxxx  Is this projected  Long,Lat  data? Mike On 2/5/2014 12:25 PM, Randal Hale wrote: So I work with Forestry guys and we do some very similar things when georeferencing. You need a good point spacing - and typically I describe that as a point at each coner of the image you are going to georeference plus one for the middle or (sorry for using this example but they have really good docs) - http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Georeferencing_a_raster_dataset If it were me I would do this: 1. go to USDA Datagateway - http://datagateway.nrcs.usda.gov/ - and download a NAIP image of your Area (sorted by county). It will be sid format (probably) - so if you are on windows you should be OK for opening up the image. 2. Use that to georeference the Google earth Screenshot. It will give you a lot more control points than just your GPS. GPS can be notorious for not quite being right if you didn't way point average - my forestry guys GPS property corners and that makes me not happy every time they do it. Both Google and Bing are good and the open layers plugin rocks - but - both image layers aren't captured (at least to me) with mapping in mind - i.e. they may be questionable. OR 1. Download the GPX data from your unit using either QGIS or DNR GPS 2. Convert to shapefile. 3. Create your contours there using a new shapefile (digitize them in again). I know I just glassed over a ton of technical by doing a 1 2 3 type scenario but I think (just my opinion) there's more hair pulling than you need to be experiencing (For the record I'm bald so I know all about hair pulling). Yell if you need more help either off list or on list - I hope some of this at least pushes you in a good direction. Randy   ----------------- Randal Hale, GISP North River Geographic Systems, Inc http://www.northrivergeographic.com 423.653.3611 rjh...@northrivergeographic.com <mailto:rjh...@northrivergeographic.com> twitter:rjhale http://about.me/rjhale On 02/05/2014 12:04 PM, Mike Keelan wrote: Thanks James, I got through the geo-referencing operation and  it did generate a new modified layer based on my .jpg.  However the new layer is badly distorted/stretched, (I used 4 coordinate Garmin GPS reference points), and it is not in the right location.  I can only find it by zooming to that layer extent.  I'm wondering if my coordinate data from my Garmin is consistent with what the geo-referencing program uses?  My Garmin data is xx.xxxxxx and it uses negative numbers to represent East instead of West.  Or, might there be an accuracy issue? I know my Garmin way-point data is good because it overlays on my Ortho almost perfectly as a separate layer. Spatial_Reference_Information:   Horizontal_Coordinate_System_Definition:     Planar:       Grid_Coordinate_System:         Grid_Coordinate_System_Name: Universal Transverse Mercator         Universal_Transverse_Mercator:           UTM_Zone_Number: 16           Transverse_Mercator:             Scale_Factor_at_Central_Meridian: 0.999600             Longitude_of_Central_Meridian: -87.0             Latitude_of_Projection_Origin: 0.0             False_Easting: 500000             False_Northing: 0.0 Mike K On 2/3/2014 8:28 PM, James Wood wrote: Mike, Here is a good tutorial overview of the georeferencing tool in QGIS: http://qgis.spatialthoughts.com/2012/02/tutorial-georeferencing-topo-sheets.html   If the image is not in coordinate space, it will not line up with your other data. so this operation will be necessary.   Also, just as a side, I would think that an export from Powerpoint would degrade image quality (depending on the original). I would look at and maybe try for future use The Gimp (which is an open source, free Photoshop-type application). It will give you more control on export of not only various output formats but also pixel and color depth, and the like. The official site is http://www.gimp.org/.   Best Regards, James   Date: Mon, 3 Feb 2014 19:59:14 -0500 From: tmike.el...@comcast.net To: t...@wildintellect.com; etourigny....@gmail.com CC: qgis-user@lists.osgeo.org Subject: Re: [Qgis-user] How do I register a Google Map? OK, I installed the Open Layers plugin and it works very nice but it won't do what I need, so let me be more specific and see if there might be a remedy. The contour lines that I want were actually obtained using a hand held Garman GPS.  The Garman data was overlaid on the Google map, (with water depths),  special integration,  then that map was exported as a Jpeg, then imported to PowerPoint where a visual interpolation was done to make the final set of contour lines for the various lake water depths. My desire is the digitize these contour lines as a set of separate layers. ie 5' deep, 10' deep, etc.  There are many good uses for these layers,  but they must be accurate as to location and size.  I don't think I necessarily need spacial info on the "map"/Jpeg if I can get the whole map in the right position, and size, so I can do the digitizing (which would then have the spacial info).  Then I can discard the Jpeg. Is it hopeless? Mike K      _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user

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