App for fencing property

“I am trying to find a app that I can use to find property corners and go from one corner to another in a straight line ( for fencing ) I have good surveys and legal descriptions to enter for my property. I would like to use my IPhone for this.”

With the legal descriptions and the coordinates of the point of beginning, you could create a deed plot in the Deed Calls & Stakeout app then use the Line Stakeout function to help you walk along the boundary line to find the property corners.

Now, the iPhone GPS is accurate to about 30 ft. An external GIS-grade Bluetooth GPS, such as the Dual XGPS-150A or a Bad Elf GPS, usually claims 2 – 5 meters accuracy (about 6 to 15 ft). You will need better accuracy for fencing a property boundary. You could use iCMTGIS PRO in conjunction with a high-precision GNSS receiver (such as a SXBlue Platinum or an EOS Arrow). The high-end GNSS receivers are very expensive. There are places that rent them out. You might check with them to see if the total cost justifies the one-time use.

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Logging GPS coordinates to match existing site information

“I am collecting coordinate points for grave sites. I have an excel spreadsheet that lists the names, dates and other data about each gravesite and I want to attach coordinates to each grave.”

Normally you would create a Feature List for the gravesites and use the titles of your spreadsheet as the Attribute field names. Then you would use the GPS/GIS data collection procedure to record the location as well as the associated information. In your case, you already have the information for the graves. Therefore, you could just log the GPS positions then import the point attributes using Feature ID as the key. However, the following method might work better for your application.

1. To your spreadsheet add two additional columns, titled Latitude and Longitude, and fill them with the coordinates of a certain location, such as 35^30’00.00N for all the latitudes, and 82^50’00.00W for all the longitudes.

If you want to assign a Feature ID to each record, then insert a column before the first column of your spreadsheet, title it Feature_ID, then fill in the ID numbers.

2. Export the data from your spreadsheet to a text file, such as graves.txt.

3. In iCMTGIS PRO create a new Point Topic named Gravesite. Use Topic – Edit Topic to add these two built-in Attribute fields: Position Y (latitude) and Position X (longitude), so that the coordinates will show up in Sheet View.

4. Use Topic – Import Text File to import the data from your text file to the Gravesite Point Topic. The import options that you select must match the contents of your text file. At this time, all the imported points will overlap because they have the same coordinates.

5. Turn on Sheet View.

6. Select the first gravesite record in Sheet View and walk to that gravesite. Tap the Feature Properties button then tap on the Update button to log the actual position of the gravesite. The default session time is 20 seconds, during which you will stand still to log the data. You may specify a different session time. The app will average the GPS fixes to yield an average position. Then select the second gravesite in Sheet View and walk to it to log the position. Continue the process until all site locations have been updated.

How long to occupy a point for optimal accuracy?

“I am using your app for iPad to store points from the EOS Arrow Gold. How long do you recommend I set the time session for one point to obtain optimum accuracy?”

To improve accuracy, it is best to let the GNSS receiver track satellites for about 10 minutes after you have turned it on, before starting to record position data.

With real-time SBAS corrected GPS data, it is not necessary to use a long point session time. Many use a session time of 5 – 10 seconds.

We sent the question to EOS, and here is their reply:
“Depends on the conditions. If in the wide open with clear view if the sky, then just a few seconds is fine (the “few seconds” (i.e. about 3 to 5) is just to make sure the rangepole is levelled).

If under light canopy then it might be wise to do a longer averaging session based on estimated accuracy from the Arrow.”

Which vertical datum am I using in iCMTGIS PRO?

“How do I tell which vertical datum I am using. I am having an issue with several different GPS’s matching on points. The elevation of each one is different by about 5.7 feet. So how would I determine which vertical datum I am using?”

The vertical reference for North America is the NAVD88.

GPS receivers measure the ellipsoidal height (HAE) and use a rough geoid model to convert it to the orthometric height (MSL). The computed orthometric height depends on the geoid model built into the GPS receiver.

Our PC software is able to use the Geoid12A files (1’x1′ grid) to compute orthometric heights that more closely conform to the NAVD88 reference. We have converted the Geoid12A (.bin) files from NGS into our proprietary format to save file space. These files use the file name extension .g1. The Geoid12A and Geoid12B are slightly different in a few areas, mainly in Puerto Rico and the southern tier states along the Gulf Coast.

iCMTGIS PRO is also able to use the .bin or .g1 geoid separation files. To use a Geoid12B binary geoid separation file (e.g. g2012bu6.bin) provided by NGS for your region of interest, please transfer it from your PC to the Documents folder for this app then close this app and run it again. If you have the PC-GIS X software program, then you can copy the .g1 file for your region to the iCMTGIS PRO Documents folder. The CMT *.g1 files take up less space than the NGS binary files.

After you have restarted iCMTGIS PRO, select Main Menu – Setup – Coordinate System to see the geoid model being applied. By default the app uses the built-in 30’x30′ grid files. With an applicable geoid file (1’x1′) available, the app will automatically use it for the orthometric height computation.

Exporting Shapefiles and DXF

“I am running iCMTGIS Pro, and trying to export to a shapefile into a folder, and copy that onto my pc. . . . I cannot drag and drop the folder from itunes to my pc (windows). . . I am trying to export everything to autocad, but I cannot use the dxf export due to it not saving the sub-attributes of my points/lines.”

1. In iTunes, please scroll down then click on the “Save To” button to save the selected file or folder to your PC.

2. When exporting to DXF, please mark the 3D and In Block options. After you select In Block, the “With Attribute” check box will be displayed. You can mark that check box to export the Attributes/Values to DXF.

What do I need to do to use, and collect, coordinates in decimal degrees as opposed to degrees minutes seconds?

In your iCMTGIS PRO app select Main Menu – Setup – Elevation and Angle. For Angle Unit select Degree.

Select the second icon from the left side of the Tool Bar at the top. This is the Topic Menu icon.

Select Edit Topic.

To see the coordinates displayed in Sheet View, add these two built-in Attribute fields: Position Y (latitude) and Position X (longitude).

In the Sheet Update screen, for Latitude and Longitude a default value will show in the Dec. Digits field when Field Type is Decimal. You will want to change it to 6.

Same with the Farming GPS GIS II/III, Forester GPS GIS II/III, Utility Data Collection and Wetland – Stakeout apps.

What to do when deed description does not provide bearing information

       EXAMPLE FOR CALCULATING BEARING FROM INTERNAL ANGLE

A Deed Calls & Stakeout user is baffled by an old property description that refers to a stretch of a certain road and specifies internal angles instead of bearings. He is able to stand at the point of beginning and obtain the approximate GPS coordinates for it.

Applying the Measure Distance function on the displayed Map, we were able to get the approximate bearing of the road segment. Then calculating the bearings for the remaining calls becomes an exercise in geometry and Deg-Min-Sec angle arithmetic operations. The bearing of each leg will need to be computed by using the bearing of the previous leg and the internal angle provided in the deed description. One will need to keep in mind that there are 60 minutes in a degree and 60 seconds in a minute.

As the bearing of the first leg determined by Measure Distance refers to true north, you can set the value of the Orientation field to 0.

The resulting deed plot can only be used as a rough reference as there are several sources of error:

1) The point of beginning may be at the wrong location as the user may not have used a high-precision GPS receiver to record the position.

2) The bearing of the road segment obtained from Measure Distance may be slightly off.

3) The printed value for one of the angles is partially illegible.

4) There may be some error in the old survey data, resulting in a closure error of about 11 ft.

Using the Measure Area tool, we see that the area comes close to the published value.