Things You Didn’t Know About GPS: By Calum McClelland

In this week’s newsletter from NGS CORS there is an article that you might find interesting to read. You can click on the following link:

https://www.ngs.noaa.gov/CORS/news.shtml

and look for “NOAA-NOS-NGS-CORS Weekly Newsletter
Created On UTC Date: Tue Apr 18 20:19 2017”

In the Newsletter scroll down until you see “Things You Didn’t Know About GPS: By Calum McClelland”

GPS Reliability

By now you’ve probably learned that one should not rely entirely on GPS while traveling. Here’s a somber reminder.

https://www.theguardian.com/technology/2016/jun/25/gps-horror-stories-driving-satnav-greg-milner

iCMTGIS III for doing power/light poles inventory

“I am interested in the iGPSGIS however I don’t know much about GIS and I don’t want to spend money unless I know it will work for my application. I want to open a map out in the field and inventory power/light poles, and document their condition, type, height, color and take a picture, as well as get a X,Y,Z coordinate. I then need to save the file and provide it to a City via an ArcGIS layer file. Will your software allow for this? Is it easy? I tried a free trial of ArcGIS and it’s so hard that I can’t do anything. I hope your software can help. . . . How many data fields can I save for 1 point?”

It appears that you are looking for a GPS/GIS app to run on your iPhone.

Our iGPSGIS II app only runs on the iPhone; it does not run on the iPad. Our iCMTGIS III can run on the iPhone as well as the iPad. iCMTGIS III has many more functions than iGPSGIS II.

Both apps can let you log the X,Y,Z coordinates of power/light poles and document their conditions, type, height and color. Both apps can export the Feature data as Shapefiles for use in ArcGIS.

iCMTGIS III will let you take a picture and link it to a Feature, while iGPSGIS II does not provide that functionality. Also, iCMTGIS III will let you load a GeoTiff map to use as off-line background map.

I am attaching a copy of the Help documents for iGPSGIS II and iCMTGIS III so you can make a comparison. Many customers come to us because our software is easy to use.

As you can see, you can set up many fields in the Feature List to facilitate data collection.

How to digitize a point, a line or an area over a map?

With many of the CMT apps, you can draw a point, a line or an area by tapping or dragging on the iPad or iPhone screen. This seems quite basic, but beginning users who have not read the instructions may be stumped because they are not yet familiar with the concept of Topic layers, which is employed in those CMT apps that provide a Topic View and a Sheet View.

To better manage your GPS/GIS data, point-type features like buildings or trees should be placed on a Point Topic layer; line-type features like roads and rivers should be on a Line Topic layer; area-type features like stands, parks and lakes should be added to an Area Topic layer. Please view this Youtube video to see the procedure for creating a Topic layer and adding some features to the active Topic layer.

You can turn on the built-in Apple map when wi-fi connection is available. Under the Main Menu select Map then select the desired map display mode.

Polygons converted to Shapefiles using kml2shp online

“Q2. I imported a polygon with 12 corners (110 ac area in Pennsylvania) (KMZ from GoogleEarth converted to shape with kml2shp online). The imported polygon has two additional 14 points, one located near the south west coast of Africa. Any polygon imported as escrowed contains one point in the South Africa location. How o I deal with this.”

There is a bug in kml2shp online.

Your polygon with 12 corners will show 13 nodes in Contour-Volume-Stakeout and any of our other apps that imports Shapefiles. This is normal – nodes 1 and 13 are the same to close the polygon.

The problem is that, when converting a polygon, kml2shp online always adds one extra point with 0 Lat/Lon.

You can resolve this issue by modifying the coordinates of node14 to be the same as node13.

1) Select the polygon.

2) Tap on the Feature Properties icon to call up the dialog.

3) Change Node# to 13 and write down the LAT/LON.

4) Change Node# to 14 and replace LAT/LON with the values from node13.

Off-line GPS data collection

“I would like the ability to collect points, lines, and polygons in the field, offline, with a way to easily download them as shapefiles for use in ArcMap when I return to the office. Will I need to purchase anything else in order to do what I have indicated?”

iCMTGIS II and iGPSGIS II will let you collect points, lines, and polygons in the field, offline, and you can download them as Shapefiles for use in ArcMap when you return to the office.

As far as off-line GPS/GIS data collection and Shapefile import/export goes, iCMTGIS II or iGPSGIS II is all you need.

The questions is whether you need to have a background map displayed as reference while collecting GPS/GIS data.

When you have connection to wi-fi, you can have the standard or satellite Apple Map displayed as background map.

If you have Shapefiles for the region in which you will be collecting data, you can import those into iCMTGIS II or iGPSGIS II as off-line background reference.
If you need to have an off-line geotiff background map displayed during data collection, then you will need to get the PC-GIS 09 mapping software, which will convert geotiff images to the .pim format for use with iCMTGIS II or iGPSGIS II.

Is there a more accurate GPS receiver to use with your apps?

As you know, the built-in GPS of the iPhone and iPad with GPS are not quite accurate. It is adequate for helping you get to the vicinity of a target location or for mapping a large area to obtain the acreage. The next best thing to do is to connect the iPhone or iPad to a compatible external consumer-grade GPS device that provides 1-3 m or 3-5 m accuracy. The Dual XGPS150A, Garmin GLO GPS + GLONASS and Bad Elf Pro belong to this category.

To obtain sub-meter accuracy using your iPad or iPhone with our apps, such as iCMTGIS II, iGPSGIS II, Utility Data Collection, Farming GPS GIS, Forester GPS GIS, Stakeout iCMT, Deed Calls & Stakeout, etc., there is an iSXBlue GNSS supplied by Geneq Inc. that will work with these devices via Bluetooth connection though it is rather expensive.  Please click on this link to see the product description. (2015 Edit: EOS Arrow will also work with iOS devices.)