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 [email protected]
<mailto:[email protected]>
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: [email protected]
To: [email protected]; [email protected]
CC: [email protected]
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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