iCMTGIS PRO for soil & water application

Navigating back to a GPS point

“I am trying to find the right app for my application. What I need to do is use my iPad and Eos Arrow 100 GNSS receiver to collect and precisely navigate back to points on the ground. Getting back to the point with the subfoot precision my equipment is capable of has proven difficult with other apps because so many are based on my location being indicated by a large blue dot on an aerial photo or map. I need more precise navigation.”

As you can see from the Point Stakeout screen, there is a tiny green dot within the GPS marker to indicate the exact point location. When you get close to the target, you could turn off the Map.

For precise RTK surveying, users usually get the iCMTGIS PRO, which can get the GPS messages directly from the Arrow receiver and not have the data truncated by iOS. iCMTGIS PRO also provides many additional functions that you will find useful for your soil and water applications.

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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.

How can I make sure I’m capturing points meeting a PDOP threshold?

If you are using iCMTGIS PRO and an iSXBlue II or EOS Arrow GPS receiver, you can set the PDOP limit for GPS data collection as follows:

1. Turn off GPS from all apps on your iOS device.

2. Select Main Menu – Setup and mark the check box for “Enable the external GPS“.

3. Select the appropriate device protocol for the GPS receiver.

4. Tap on the pull-down arrow for PDOP Mask and select the desired PDOP Mask level. If you only want to record position data for which the elevation can be computed, then also mark the “3D Only” check box. Tap on OK to save the setting and close the screen.

5. Tap on the GPS icon then select “Turn external GPS on”.

Using iCMTGIS PRO and EOS Arrow Gold to collect UAV ground control point data

“I have a UAV company and do lots of inspections and mapping with my drones, when I am doing the mapping in the past I have hired crews with total stations to get me my GCP’s so now I want to do this myself. I get the X, Y and Z data from them so I can input them into my Pix4D software. I know your software allows me to collect the X and Y data but can I also collect the Z data accurately?  . . . . .  Please see the attached GCP information sheet I get from survey companies. As long as I can get this data it will be great.”

These appear to be the coordinates for Point Features. So, you will want to first set up the coordinate system and distance unit to use. If you are using UTM, select the proper zone.

Now create a new Point Topic and give it a name, such as GCP (for ground control point). Then Edit the GCP Topic and add the built-in Attributes: Position_X, Position_Y and Elev_Z as well as the GCP ID attribute.

With the GCP Topic selected, turn on GPS and record a few points. After ending the point data collection, you can turn on Sheet View and look at the data in a spread-sheet arrangement.

You can export the point coordinates and attributes data to Shapefiles or a text file.

As the GCPs are control points, you will need to use the Arrow Gold GNSS receiver in RTK mode to get better accuracy.

Under Setup – GPS, select “Enable the External GPS” and select the protocol for the EOS GNSS receiver. This way, you will be able to see the RMS error of the GPS data output by the GNSS receiver displayed at the top of the Map View screen.

How to use iCMTGIS III to check GPS accuracy

“I have purchased the iCMTGIS III and I am using a TIFF image as a background map. I am having problems with the GPS not very close to a known point. Do you have any suggestions? I am using a Bad Elf Pro+ as an external GPS it says it is supposed to have 3-5 meter accuracy. Do you suggest another GPS? Is there only one place to change coordinate system or is there other parameters that may need to be changed to get acceptable accuracy?”

Does your iPad come with GPS? Perhaps the iPad is using its internal GPS, which has poor accuracy. Please turn off GPS from all the apps on your iPad. Then, with the Bad Elf Pro+ connected to your iPad and turned on, run iCMTGIS III and select GPS – Turn on GPS.

Another way to ensure that the iPad uses the external GPS is to turn on the Airplane mode under the iPad Settings. For details, please see our blog post at:
https://icmtgis.wordpress.com/2014/03/05/using-an-external-gps-with-icmtgis-ii-on-ipad/

To check the accuracy of the GPS receiver against the LLA coordinates of a known point or survey mark, you could first create a Point Topic then add a Point by using the Add Point by Coordinates function from the Tools menu. Enter the latitude and longitude of the known point. With the Bad Elf GPS having been turned on for a few minutes, check the location of the GPS marker against the known point. The published accuracy is an average value.

To record a Point Feature, please use GPS – Collect and log GPS point data for 5 minutes or longer. The app will compute and display the average point position. Measure the distance between the recorded point and the known point.