Symbol used for representing recorded GPS Features

A customer reported that he had collected a number of points using iCMTGIS Pro and Arrow 100. Although the Topic in his Feature List have specific symbols assigned to them, the recorded points were displayed using the default blue dot symbol.

We have determined that this is a software bug in some of our apps. We will work on fixing this issue. In the mean time, you can click the “Pattern” button to select the desired symbol before storing data.

Which coordinate system should I use to collect GPS data?

“Is this the standard configuration ( WGS 84 LLA ) in iCMTGIS pro? Will it transfer back and forth in different coordinates? Or should I collect data also in NC State Plane since shapefiles are NC SP?”

Internally our software stores location data in WGS 84(1674)/ITRF08.

The options under Setup – Coordinate system is for you to select the coordinate system for displaying the position data.

Many people use the WGS 84(1674)/ITRF08 system on the iCMTGIS PRO because they are familiar with it.

You can set the iCMTGIS PRO to NC State Plane to collect GPS data if you wish to see the coordinates displayed in that system.

The important thing to remember is that when you are combining data (such as by importing Shapefiles), you must make sure that they are in the same coordinate system. You cannot add apples to oranges and expect to get a sum that represents the total number of oranges. In many cases you don’t have the option to change the coordinate system of the Shapefiles at their source. Therefore, our iCMTGIS PRO and PC software provides the ability to switch to the coordinate system used by the Shaepfiles to be imported.

Some people also use geo-referenced images in .tif format. Here again, you will need to find out what coordinate system the .tif file refers to before trying to load it into our software.

For people who make use of data from a RTK network, the Datum must be set to match that used by the RTK base station.

How to record points for contouring an area using iCMTGIS PRO

“I went to GPS > Collect, but I might have collected a line after that, rather than a traverse. Would that still be usable to generate contours?”

1. You can disconnect a Line Feature into Point Features by selecting that Line then using Utilities > Disconnect. Each node of a Line Feature is just one GPS fix. It may not be that accurate.

2. GPS > Collect > Traverse > Store will let you select a reference (starting Point) then enter slope distance, slope angle and bearing to create a new Point. You could generate new points this way when GPS signals are weak.

3. To properly record points for contouring, you will want to use GPS > Collect and record each point for a session of at least 30 seconds to obtain an averaged position. Generally, a longer session time results in better accuracy.

4. One thing to keep in mind is that vertical distance accuracy of GPS receivers is generally 3 times worse than horizontal distance accuracy.

How to map an area using iCMTGIS PRO without using a Feature List

A Feature List can help you do certain jobs more efficiently, but it is not required for mapping a Feature. Following is a general procedure for mapping an Area Feature.

You will need to have either a built-in GPS receiver or an external GPS receiver connected to your iPad or iPhone device. Dual XGPS-150A, Bad Elf GPS 220 and Garmin GLO claim about 2 – 5 meters accuracy. EOS Arrow Gold and SXBlue Platinum can achieve sub-meter or higher accuracy.

To map your Area Feature, first create an Area Topic after tapping on the Topic Menu and selecting New Topic.

Then, tap on the GPS icon at the top, select Turn GPS On.

If GPS is available, you should hear beeps and see a GPS marker (a little red triangle) moving on the screen. This means the app will be able to get the GPS positions. You can wait a few minutes for the GPS to stabilize after it has been turned on.

Now tap the GPS icon and select Collect. Select the Area Topic into which to record your Area Feature. Confirm the default setting of Dynamic Area with 1 second interval between the recorded nodes.

In the next screen tap the Store button then start walking along the boundary of the area. When you get back to the starting point, tap the Stop button. You should see the area plotted on the screen.

If you wish to store certain things like light poles or wells along the path, then tap the Nested button. This will halt the Area Feature and let you log a Point Feature. Enter a name for your point. (If you have created the Point Topics beforehand, then you can select it from the drop-down list.) Confirm the Static option. Time Session is how long you want to stand at that point to collect data. The app will average the GPS fixes collected during that time to compute the position. Generally, more GPS fixes yields a more accurate result. When done recording the point, the app will prompt you to continue with the Area Feature or record another point.

If you are using a high-precision GPS or GNSS, such as EOS Arrow Gold or SXBlue Platinum, you could select “Enable External GPS” in the GPS Setup screen. This will tell the app to display the GPS status and position quality information at the top of the screen.

App to help plant trees?

“I am wondering if any of your programs could be used in my tractor as a way to guide me in driving a straight line when planting Christmas trees? Even if it doesn’t help me row by row could it be used to help me lay out a planting? Help to drive the first line across a field?”

The GPS system you will need to guide a tractor along a line to plant Christmas trees requires a high-precision GPS receiver used in conjunction with an app that will let you record a few reference points, draw the line on the map and guide the tractor along the line.

The actual equipment and app you select will depend on the accuracy you wish to achieve. Of course, a high-accuracy system comes with a high cost.

The SXBlue Platinum and EOS Arrow Gold GPS receivers can be used with iCMTGIS III to achieve sub-meter accuracy.

The SXBlue Platinum and EOS Arrow Gold GPS receivers can be used with iCMTGIS PRO and a RTK network to achieve cm-level accuracy.

As there will also be visual cues to guide the tractor, do you think sub-meter accuracy will be sufficient for you?

Both iCMTGIS III and iCMTGIS PRO will let you load a geo-referenced background map (*.tif. *.pim or *.bmp). These are useful as a general reference, but they are not accurate enough to let you pin-point your first point or line by digitization.

You could use iCMTGIS III with a SXBlue Platinum or an EOS Arrow Gold GPS receiver to record the property boundary and the starting point to sub-meter accuracy. iCMTGIS III and iCMTGIS PRO will let you create a grid over the property to indicate where the trees are to be planted.

iCMTGIS III and iCMTGIS PRO provide the Stakeout functions to guide you along the grid lines. These apps will display how far the tractor deviates from the line. You could also set up the apps to keep beeping as long as the tractor stays on the line within the specified tolerance.

Recording property lines

“I have recently purchased a 19 acre field/forest and have a new survey PLAT with freshly marked property pins. I would like to permanently record the data points onto a GPS device such as an iPhone for when the markers are removed (to install fences, argue with neighbors over hunting areas, etc.). I need the app to be able to guide me between the pins while walking with the GPS.”

For your intended use, you will need a high-precision GPS receiver. The GPS built into the iPhone is good to about 30 ft or worse in some situations. This is in adequate for settling arguments between neighbors.

The Deed Calls and Deed Calls & Stakeout apps are for drawing the deed plot by entering the deed calls (bearing and distance information). The Deed Calls & Stakeout app will then be able to guide you along this deed plot. To correctly place the plot on the map on the iPhone, you will need to have the GPS coordinates for the first point. These two apps do provide a “Pick GPS” button for you to grab one GPS fix. However, it will be an approximate position if you are just using the iPhone built-in GPS.

As you want to record the positions of the stake points and also be guided to walk between the pins, the system to use is a high-precision GPS receiver like the iSXBlue II+ GNSS or the EOS Arrow Gold with an iPhone or iPad running iCMTGIS III or iCMTGIS PRO. The iCMTGIS III and iCMTGIS PRO apps will let you record a position by taking many GPS fixes and averaging them. They will also let you record an irregular property boundary by walking along the boundary. They provide the Point Stakeout (to guide you to the pins later) and Line Stakeout functions (for guiding you along the property boundary later). They also provide the Deed Calls functionality.

In summary, it boils down to the desired accuracy. Using an iPhone running Deed Calls or Deed Calls & Stakeout app might be adequate for a realtor or a forester (to do a quick approximate deed plot). Deed Calls & Stakeout is useful for someone who needs to find old stakes based on a deed plot. To record accurate stake positions, you will definitely need a much better GPS than the iPhone GPS. If you can accept a 2 m – 5 m (6 ft – 15 ft) error, then you could consider using the less expensive Dual XGPS-150A or Bad Elf GPS.

Apps for recording GPS points

“I have downloaded your Deed Calls application and it works great. However, I am looking for an additional feature and I’m unsure which product will get me what I would like. I need to enter deed calls AND use the GPS to set points all in the same area. With deed calls, it seems to allow me to set the starting point with GPS, but after that, seems that I have to have the deed calls.”

The PickGPS function just grabs one GPS fix. This, in combination with the GPS that comes with the iPhone and iPad devices, which lacks accuracy, will not give you an accurate starting point for your deed plot. You will want to check the deed plot against the satellite map to see it is located approximately correctly.

The Deed Calls Pro app provides both the ability to create a deed plot and the ability to digitize points using PickGPS.

Our Forester GPS GIS III and Farming GPS GIS III for use with iPad devices and the iCMTGIS III and iCMTGIS PRO apps for use with either iPhone or iPad devices, provide the Deed Calls function plus a GPS Point data collection function that will let you record multiple GPS fixes at one location and compute the average position.

The accuracy of your work will still depend on the precision of the GPS receiver you use. Some of our customers use the Dual XGPS-150 or the Bad Elf GPS 2200 to get 2-5 meter horizontal accuracy. Other customers use high-precision GPS receivers (iSXBlue II+ GNSS and EOS Arrow GNSS) to obtain better position accuracy.