Field Validation Background: When creating complex GIS databases, it is essential that all or a significant portion of the digitized (or acquired) data should to be validated; this is done with various methods but the most common is “field validation”, visiting the location and comparing GIS data to your observations. Remote Sensing often calls this process “ground-truthing”. To accomplish verification you have to have some very detailed version (copy) of your data available in the field to compare with your observations. You also need a process to record the results of your observations. Initial concept: Prepare your data within a GIS to use in the field. This could be a very detailed printed copy of a map of your study area or some electronic version (hand-held device). The key issue is that all of the data you need to verify should to be “OBVIOUS” on the map or easily found on the handheld device. This means that “scale” is very important. You must print a very detailed large-scale map or have the ability to change the scale on your hand-held device. (zoom-in). The common issue with exporting data is to render your data at a level of detail to support the required scale change (zoom-in/out). 1 st step: Prepare a map of your study area (or the area in which you will perform the validation). Create a PDF of your area. PDF’s are useful as you can provide details of many relevant layers. Use of aerial imagery is also common but often you need to limit the amount of information to just what is needed for validation and only enough related layers to maintain your orientation.
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Field Validation
Background:
When creating complex GIS databases, it is essential that all or a significant portion of the digitized (or
acquired) data should to be validated; this is done with various methods but the most common is “field
validation”, visiting the location and comparing GIS data to your observations. Remote Sensing often
calls this process “ground-truthing”. To accomplish verification you have to have some very detailed
version (copy) of your data available in the field to compare with your observations. You also need a
process to record the results of your observations.
Initial concept:
Prepare your data within a GIS to use in the field. This
could be a very detailed printed copy of a map of your
study area or some electronic version (hand-held device).
The key issue is that all of the data you need to verify
should to be “OBVIOUS” on the map or easily found on the
handheld device. This means that “scale” is very
important. You must print a very detailed large-scale map
or have the ability to change the scale on your hand-held
device. (zoom-in).
The common issue with exporting data
is to render your data at a level of
detail to support the required scale
change (zoom-in/out).
1st step:
Prepare a map of your study area (or
the area in which you will perform the
validation).
Create a PDF of your area. PDF’s are
useful as you can provide details of
many relevant layers. Use of aerial
imagery is also common but often you
need to limit the amount of
information to just what is needed for
validation and only enough related layers to maintain your orientation.
Export the PDF in the highest
resolution possible at the largest
scale possible.
In this example, I used a “tabloid
size” at 600 DPI.
You should also ensure that the
Advanced Tab (Export Map as
PDF) is set to “Export Map
Georeference Information”
2nd Step: Move the PDF to the hand-held device.
There are several methods to move a PDF (in this case a geo-
spatially enabled or GeoPDF) to a hand-held. A common approach
is to email the PDF as an attachment. For this example we use and
“App” that transfers files over a FTP WiFi connection.
Using an Android based device, Nexus 7, start the installed “App” ES
File Explorer.
If you do not see a screen that looks like the one to the right, swipe
across the screen to display the “desktop” with ES File Explorer.
Below (left), find the “down arrow” in the middle of the screen and
it will bring up a full screen; like the one on the right. Select the
“View on PC” tool.
Select the “View on PC” tool.
On the left screen (below) tap the blue button at the bottom “Turn On”
Then note the ftp address. Shown
to the right is an EXAMPLE, your
numbers will be similar but not
exactly the same.
This is an FTP address.
On your computer (on the same
WiFi as the hand-held) navigate to
File Explorer (not an internet
browser).
Type in the search bar EXACTLY what you see on the hand-held eg: ftp://10.132.109.73:3721/
You will now see the contents of the hand-held (as shown above right).
Copy your geo PDF map of your area to be verified to the PDFMaps folder on the hand-held device.
Remember the ES File Explorer connection process as you will use the “opposite” to copy your field
verified data from the hand-held to your computer.
On the handheld, open PDF Maps and add the PDF map you just transferred (see next page).
Import your PDF map from the PDFMaps folder on the hand-held unit.
When finished importing, open the PDF and explore the map.
An example of a geospatially enabled PDF map
in Avenza Maps (PDF Maps)
Zoom in or pan around.
Find the features you wish
to verify.
Notice the cursor (above) is colored in “orange”. The cursor color is user selectable. Use your finger to
move the map around “under” the cursor.
Verifying points (pins) will only be dropped at the cursor location. If you drop a pin right now, it will be
located at your cursor location. Pins are dropped by tapping the “pin” icon at the top left.
When you have an active GNSS position, and you are “on the map”, it will display as a “Blue Dot”
If you walk around on the map the “Blue Dot” moves displaying
your current position. If you wish to drop a pin at your current
position you need to center the cursor (now shown in BLACK)
over the “Blue Dot”.
You do this by pressing the
“target” icon.
Then drop the pin
Practice dropping a pin, You
should erase practice work
before field verifying your
features.
As you drop a “pin” select the right arrow to open the detail screen
This detail screen the “generic”
Placemark screen.
We will use a “custom” screen with
attribute appropriate for verification
To delete a “pin” aka Placemark, select the “trash” icon in
the upper right of the Edit Map Feature, when Placemark detail is displayed
Custom Attributes:
For our work we will be collection verification details for several “different” types of features.
For each type we should first create a “folder” and then add unique detailed attributes to the features