WEBVTT

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Welcome to OPUS Projects training, reconnaissance and project planning.

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Please note the current version of OPUS Projects may look

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slightly different than shown here.

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The functionality generally remains the same.

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Efficiency and success in OPUS Projects depends on knowing the

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guidelines, standards, and software, then planning and executing the survey.

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There are 5 basic steps to success in a project.

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What is the project's objective?

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How accurate does the survey need to be to accomplish

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the objective?

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What existing survey marks will be used as control to

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tie the project to the National Spatial Reference System?

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The NSRS?

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What new survey marks are needed, where should they be,

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and how many?

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What survey method will most efficiently serve the project?

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OPUS Projects is an excellent tool if your project objectives

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include any of the following: verifying published coordinates or heights

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on existing marks, adjusting a GPS survey network and aligning it

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to NAD 83, NAVD 88 or other datums in the

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NSRS, or establishing and publishing new geodetic control in the

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locations where you need it.

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Geometric coordinates are always considered a triad: latitude, longitude, and

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ellipsoid height, so ellipsoid height accuracy always plays into the

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equation whether you want orthometric heights.

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In general, the vertical requirements will drive the survey design

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because GPS is more accurate horizontally than vertically.

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If the project's objectives are restricted to geometric coordinates, then

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the NOA CORS Network, NCN, and local passive marks will

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suffice.

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But if the project's objectives include orthometric heights, then valid

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existing local vertical control must also be observed.

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Note that the overall planning process is similar for both

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types of projects.

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OPUS Projects is designed to be flexible and adaptable, but

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it's the user's responsibility to ensure that OPUS Projects is

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suitable for the particular survey objective.

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NGS defines the following three classifications of network and local

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accuracy for GNSS geodetic control surveys, which will be submitted

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to NGS for review and publication.

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These are primary, secondary, and local.

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Each classification is supported by a detailed set of standards

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and specifications, See NOAA Technical Memorandum NOS NGS 92.

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Now that you know what to do the project objective

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and how well it must be done, the classification of

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intended accuracy, you can set or identify new marks for

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your survey.

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Choose your horizontal control by selecting CORS and recovering passive

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marks in the project vicinity.

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Choose your vertical control distributed throughout the project by recovering

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local valid benchmarks, observing the spacing requirements, and choose a

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survey method.

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Set the most stable, permanent, publicly accessible mark possible for

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the local conditions.

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The NGS benchmark reset procedures contain some diagrams of suggested

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settings, and FGCS Annex P may also be helpful.

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The best horizontal control will be the CORS and permanent

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passive marks in the project vicinity.

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Selection of the CORS is one of the more critical

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aspects of designing your project.

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OPUS Projects automatically loads CORS into each session from the

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OPUS Static solutions, but you need to make the final

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selections.

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Best practice is to check the quality of the CORS

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prior to starting your project.

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The OPUS Projects user manual provides more details.

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NGS recommends a hub design for each session.

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Designate a local CORS close to the project area to

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act as the local hub within zero to 200 kilometers

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of the user marks.

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Use three or more local CORS to have redundant control

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within zero to 300 kilometers of the hub.

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Include one or more distant CORS to act in tropospheric

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corrections located 400 to 800 kilometers from the hub.

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Data must be available at the time of the survey.

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Brief data gaps of less than one hour are generally

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acceptable, but data gaps of several hours are not acceptable.

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Longer time series likely leads to better coordinates.

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Check the CORS' Position and Velocities page for computed velocities.

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The page might instead state published velocities or modeled velocities.

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The CORS should have good network accuracy.

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See the CORS data sheet.

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Ideally less than 1 1/2 centimeters horizontal, less than 3cm

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ellipsoid.

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The CORS short term plots should show low RMS consistent

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data and no bias.

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This example CORS is poor in all respects.

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This example CORS is good in all respects.

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Selected distant CORS 400 to 800 kilometers away for tropospheric

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modeling.

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The Place X button on the CORS map draws a

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250 kilometer radius circle to guide selection.

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The tutorial project has 8 CORS which were automatically included

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as the OPUS static data were uploaded.

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As the diagrams show, 2 CORS are not acceptable.

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Let's look more closely on the next 4 slides.

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These two CORS are acceptable.

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These two CORS are not acceptable due to extreme bias

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in the up component.

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These two CORS are acceptable, and these two CORS are

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acceptable.

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All CORS network accuracies are less than 1 1/2 centimeters

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horizontal and less than 3cm ellipsoid.

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All CORS have computed velocities.

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For most projects, plan to use the same hub in

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every session, but for large projects you may need more

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than one hub in a session.

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If user marks are spread out so far in a

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session that it is not possible to have one hub

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within 100 to 200 kilometers of the user marks, then

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designate more hubs at about 200 kilometer spacing.

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For multi hub projects, designate the same CORS as hubs

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in every session.

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HUB1, HUB2, HUB3.

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This will limit hub to mark baseline lengths to 100

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kilometers or so.

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Here's an example of a large project showing several hubs

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and distant CORS.

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Having optimized the project design and pre selected the CORS,

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the existing passive marks in the vicinity should be identified,

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recovered and considered for inclusion in the project.

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NGS provides several tools to aid in locating nearby marks.

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The NGS Data Explorer. The NGS web map. In either

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product

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read the introductory splash screen for basic instructions on usage.

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Use the NGS Passive Mark page to get more detailed

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information on each mark of interest.

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Here's an example of an NGS Passive Mark page and

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the detailed information available for the selected mark.

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Examine the NGS data sheet to find published positions and

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method attributes.

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This mark would be constrainable as horizontal and vertical.

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This mark would be constrainable vertically but not horizontally.

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This mark would be constrainable as horizontal but not vertical.

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An OPUS share mark would not be constrainable as horizontal

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or vertical.

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What marks could be used to tie your survey to

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NAVD88?

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Leveled heights of first or second order are best.

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Next, you could consider using GPS drive marks, but only

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if labeled as height mod and published to two decimal

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places.

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It's time to hit the field.

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Never assume that marks will be found in good condition.

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Do they have clear unobstructed sky view 10 to 15°

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above the horizon?

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OPUS Projects will not process satellites below 10°.

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Send in mark recoveries for those marks which will not

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be in the project using the online recovery form.

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You can also send in mark recoveries for those marks

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which will be in the project using the online recovery

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form.

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But remember, if you're planning to submit to NGS, the

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in project marks must be submitted via WinDesc.

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Instead, try the NGS Mark Recovery form.

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For existing marks, you may need to request an NGS

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agency code.

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If you don't have one, you can use Agency Type

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M and default code of None.

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You'll need that agency code later to create your OPUS

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project.

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If you're planning to submit NGS, submit all three photos

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available on the Mark Recovery form and they'll be named

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correctly if you use the form.

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Submitting recoveries via WinDesc was discussed separately.

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Passive marks for horizontal control should be located within the

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nominal 100 kilometer spacing, but marks intended as vertical control

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should be located within 30 to 50 kilometers of the

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proposed new benchmarks.

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Non control or newmarks must be within a certain distance

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of two or more valid existing vertical control marks, typically

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30 kilometers.

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The maximum distance between newmarks and vertical control is between

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30 and 50 kilometers based on the two longest duration

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occupations.

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See the chart in the example.

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The average duration of the two longest occupations is five

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and a quarter hours, which allows 45 kilometer spacing.

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Let's take a deep dive on control mark spacing.

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NGS requires that you occupy benchmarks with valid existing orthometric

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heights distributed every 30 to 50 kilometers.

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A minimum of two valid control marks per non control.

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Adhere to maximum distance to vertical constraint requirements.

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Make a plot to scale of the existing and proposed

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benchmarks.

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In this example use a 30 kilometer radius.

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Then measure and tabulate the relative distances between existing valid

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benchmarks and the proposed new benchmarks.

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Highlight in each column the distances which meet the spacing

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requirements.

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In this example, only three proposed benchmarks, J, M and P,

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meet the spacing requirements.

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If more proposed benchmarks must meet the spacing requirements, then

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longer duration occupations will allow greater spacing up to 50

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kilometers.

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See the chart.

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Note that these are minimum requirements.

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It's always best to include redundant control in case one

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of your control marks does not fit well within the

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network.

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OPUS Projects supports 4 survey methods, giving surveyors a choice

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of which method will best support the project objective in

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the most efficient manner.

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OPUS Projects will accept 2 hour or longer static observation

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files in RINEX format to be processed in OPUS Static

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called OPUS PP.

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NGS has defined a GNSS Vector Exchange File Format, or

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GVX, which allows several survey methods to be submitted.

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Using GVX, you can collect raw data and post process

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vectors using local proprietary software, convert to GVX, then submit

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to OPUS Projects called GVX PP.

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You can collect network RTK vectors in the field, convert

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them to GVX, and then submit to OPUS Projects called

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GVX NRTK.

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Or you can collect single base RTK vectors in the

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field, convert them to GVX, then submit to 

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OPUS Projects.

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These are called GVX SRTK.

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NGS recommends a single hub network for most projects.

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The diagram shows that a combination of survey methods is

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acceptable and can be processed by OPUS Projects.