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

[Randal Hale]

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 rjhale at northrivergeographic.com
<mailto:rjhale at 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.
>
> 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.elhoa at comcast.net
>> To: tech at wildintellect.com; etourigny.dev at gmail.com
>> CC: qgis-user at 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
>>
>>
>>
>
>
>
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