{"id":2010,"date":"2016-06-28T18:11:43","date_gmt":"2016-06-28T18:11:43","guid":{"rendered":"\/?post_type=ht_kb&p=2010"},"modified":"2019-09-27T14:34:07","modified_gmt":"2019-09-27T14:34:07","slug":"nmea-gga-strings-in-ntrip-clients","status":"publish","type":"ht_kb","link":"https:\/\/www.use-snip.com\/kb\/knowledge-base\/nmea-gga-strings-in-ntrip-clients\/","title":{"rendered":"NMEA GGA Strings in NTRIP Clients"},"content":{"rendered":"

What are NMEA-183 GGA sentences?<\/h3>\n

NMEA-183 GGA sentences are used by NTRIP Clients<\/a> to inform the NTRIP Caster<\/a> where they are (and hence the location they require corrections for).\u00a0 The use of the GGA sentence is found most often on virtual reference station (VRS) networks and on networks using NEAR type<\/a> streams.\u00a0 It is not actually used on single baseline networks, but some SNIP<\/strong><\/span> operators use it to keep track of where the currently connected end users are located (a sort of AVL use).<\/p>\n

When connecting to a virtual reference station the NMEA-183 GGA sentence is presented by the client either at the initial connection (as allowed by NTRIP protocol r2) or once the connection acknowledgment occurs (as allowed by NTRIP protocol r1, and the most common format now deployed in the world).\u00a0 Thereafter, about every 5~60 seconds, the NTRIP Client repeats sending the NMEA-183 GGA sentence.\u00a0 The data (or at least the time stamp) should be updated, but some NTRIP Clients reuse the original sentence each time.<\/p>\n

SNIP<\/strong><\/span> accepts all valid NMEA-183 sentences and simply ignores them (unless needed in the connection is to a NEAR<\/a> type of mountPt, discussed below).\u00a0 Because all SNIP<\/strong><\/span> data streams represent connections to single baselines, there is no use for this data from clients.\u00a0 And it does no harm other than to waste bandwidth.\u00a0 [Aside–<\/strong><\/em>when SNIP<\/strong><\/span> makes a remote connection to a virtual reference station (VRS) network, it also sends a suitable NMEA-183 GGA sentence to obtain data for the location requested.]<\/p>\n

In the case of a NEAR<\/a> type of mountPt, every time the NTRIP Client sends a new GGA sentence, SNIP<\/strong><\/span> performs an evaluation of the distances to the various mountPts in the NEAR pool, and will automatically connect the user to the nearest data stream as the client positions moves and is updated.<\/p>\n

When the initial NMEA-183 GGA sentences from an NTRIP Client are received by SNIP<\/strong><\/span>, the console makes a note of it.\u00a0 After the first five<\/span> such messages, the console no longer displays this data in order to prevent mindless screen clutter.\u00a0 However the last GGA sentence for each client is always<\/span> kept and can be displayed visually on the map and textually using the List Current Users…<\/strong> button (on the clients \/ caster tab).<\/p>\n

Displaying GGA sentences<\/h3>\n

Any NMEA-183 GGA sentences from clients will be initially shown (if client connections are not being filtered at the time).\u00a0 Here is an example of such a console log report for a client that is sending this content.<\/p>\n

[SCSC02<\/span><\/b>]:\u00a0\u00a0Client #C02<\/span><\/b> [69.75.31.xxx:61969] Connected to SCSC02 <\/b>at 04:37:29 PM (local)<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 1st NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 2nd NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 3rd NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 4th NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 5th NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0Further periodic NMEA-183 Sentences will not be shown. Note:<\/b> These messages are not processed by SNIP<\/span><\/b>.<\/span><\/pre>\n
 <\/p>\n
Here is a similar example of a console log report where the log threshold has been set to “minor<\/strong>” in order to see the actual NMEA-183 GGA sentences which the client has sent.<\/p>\n
[SCSC02<\/span><\/b>]:\u00a0\u00a0Client #C02<\/span><\/b> [69.75.31.xxx:61969] Connected to SCSC02 <\/b>at 04:37:29 PM (local)<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 1st NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 Was: [$GPGGA,233732.01,3946.2000000,N,08413.2000000,W,1,00,1.0,34.073,M,-34.073,M,0.0,*4F ] <\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 2nd NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 Was: [$GPGGA,233736.95,3946.2000000,N,08413.2000000,W,1,00,1.0,34.073,M,-34.073,M,0.0,*46 ] <\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 3rd NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 Was: [$GPGGA,233741.87,3946.2000000,N,08413.2000000,W,1,00,1.0,34.073,M,-34.073,M,0.0,*45 ] <\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 4th NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 Was: [$GPGGA,233746.79,3946.2000000,N,08413.2000000,W,1,00,1.0,34.073,M,-34.073,M,0.0,*43 ] <\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 5th NMEA-183 Sentence Detected<\/b> from Client #C02; NMEA inputs are ignored <\/b>in this stream.<\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0\u00a0\u00a0\u00a0 Was: [$GPGGA,233751.74,3946.2000000,N,08413.2000000,W,1,00,1.0,34.073,M,-34.073,M,0.0,*48 ] <\/span>\r\n\r\n[SCSC02<\/span><\/b>]:\u00a0\u00a0Further periodic NMEA-183 Sentences will not be shown. Note:<\/b> These messages are not processed by SNIP<\/span><\/b>.<\/span><\/pre>\n
 <\/p>\n
Update<\/strong><\/span>:\u00a0 SNIP<\/strong><\/span> now also displays the LLH values in the more readable DD.dddd format.\u00a0 The value is also used to compute the baseline distance to the base station that client is connected to, and this value is also shown.<\/p>\n
The NMEA-183 GGA locations are expressed in the form of DDMMSS.sss\u00a0 (deg, minutes, seconds)\u00a0 which can prove hard to read for some users.\u00a0 So the location can also be expressed in a format of DDD.ddd\u00a0 (decimal degrees and fractions) as well.\u00a0 And the height is with respect the the devices local concept of “sea level” and not<\/span> the reference ellipsoid of WGS84.\u00a0 SNIP<\/strong><\/span> also orrectly handles the common “minutes-of-position” translation error found in many NTRIP Clients of having a value of “60” in the minutes field as well.<\/p>\n
Hint<\/strong><\/span>: The above display is also an effective way to use\u00a0SNIP<\/strong><\/span> to view what an NTRIP Client device is sending if there is some doubt or need to debug things.<\/p>\n
Note<\/strong><\/span>:\u00a0 Connecting to a VRS network takes time.\u00a0 One minute or more may pass between the time the connection is made and when the first data is returned.\u00a0 As a consequence of this it is important that the NTRIP Caster not time out while waiting for the initial return of data.\u00a0 Short timeout values (such as 10 seconds, the default used on the RTKLIB tool) need to be adjusted based on each network.<\/p>\n
Note<\/strong><\/span>: The location reported by the NMEA-183 GGA sentence is often not the same as the precise RTK position computed by the rover device.<\/p>\n
Plotting GGA sentences<\/h3>\n
Any NMEA-183 GGA sentences sent from your clients can be displayed (plotted) on a Google base map using SNIP<\/strong><\/span>‘s built-in map functions<\/a> as well.\u00a0\u00a0 This provides a simplistic AVL functionality.\u00a0 [Aside<\/strong><\/em><\/span>:\u00a0 If you require more advanced AVL recording and reporting, or connections to feed to a 3rd party system, please contact us about the Enterprise<\/strong><\/em><\/span> edition of SNIP<\/strong><\/span> or look at the AVL tab<\/a> features.]<\/p>\n
\"SNIPasAVL\"<\/a><\/p>\n
Need to learn more about decoding NMEA-183?<\/h3>\n
Here are a few good links that offer advice on the more popular sentences (in NMEA-183 speak a message<\/em> is called a sentence<\/em>).<\/p>\n
The classic: Glenn Baddeley’s\u00a0 – GPS – NMEA sentence information site<\/a><\/p>\n
A newer Page:\u00a0 NMEA data – Joe and Jack’s GPS Information Website<\/a><\/p>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
What are NMEA-183 GGA sentences? NMEA-183 GGA sentences are used by NTRIP Clients to inform the NTRIP Caster where they are (and hence the location they require corrections for).\u00a0 The use of the GGA sentence is found most often on virtual reference station (VRS) networks and on networks using NEAR […]<\/p>\n","protected":false},"author":13,"comment_status":"open","ping_status":"closed","template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"ht-kb-category":[112],"ht-kb-tag":[226,242,241],"class_list":["post-2010","ht_kb","type-ht_kb","status-publish","format-standard","hentry","ht_kb_category-general","ht_kb_tag-debug","ht_kb_tag-gga","ht_kb_tag-nmea"],"yoast_head":"\nNMEA GGA Strings in NTRIP Clients - SNIP Support<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.use-snip.com\/kb\/knowledge-base\/nmea-gga-strings-in-ntrip-clients\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"NMEA GGA Strings in NTRIP Clients\" \/>\n<meta property=\"og:description\" content=\"What are NMEA-183 GGA sentences? NMEA-183 GGA sentences are used by NTRIP Clients to inform the NTRIP Caster where they are (and hence the location they require corrections for).\u00a0 The use of the GGA sentence is found most often on virtual reference station (VRS) networks and on networks using NEAR […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.use-snip.com\/kb\/knowledge-base\/nmea-gga-strings-in-ntrip-clients\/\" \/>\n<meta property=\"og:site_name\" content=\"SNIP Support\" \/>\n<meta property=\"article:modified_time\" content=\"2019-09-27T14:34:07+00:00\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"5 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/knowledge-base\\\/nmea-gga-strings-in-ntrip-clients\\\/\",\"url\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/knowledge-base\\\/nmea-gga-strings-in-ntrip-clients\\\/\",\"name\":\"NMEA GGA Strings in NTRIP Clients - SNIP Support\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#website\"},\"datePublished\":\"2016-06-28T18:11:43+00:00\",\"dateModified\":\"2019-09-27T14:34:07+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/knowledge-base\\\/nmea-gga-strings-in-ntrip-clients\\\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/knowledge-base\\\/nmea-gga-strings-in-ntrip-clients\\\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/knowledge-base\\\/nmea-gga-strings-in-ntrip-clients\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"NMEA GGA Strings in NTRIP Clients\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#website\",\"url\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/\",\"name\":\"SNIP NTRIP Caster Support\",\"description\":\"SNIP NTRIP Caster Support\",\"publisher\":{\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#organization\",\"name\":\"SNIP Support\",\"alternateName\":\"NTRIP Caster\",\"url\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/wp-content\\\/uploads\\\/2016\\\/08\\\/SNIPwStreamUsers.png\",\"contentUrl\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/wp-content\\\/uploads\\\/2016\\\/08\\\/SNIPwStreamUsers.png\",\"width\":1132,\"height\":723,\"caption\":\"SNIP Support\"},\"image\":{\"@id\":\"https:\\\/\\\/www.use-snip.com\\\/kb\\\/#\\\/schema\\\/logo\\\/image\\\/\"}}]}<\/script>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"NMEA GGA Strings in NTRIP Clients - SNIP Support","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.use-snip.com\/kb\/knowledge-base\/nmea-gga-strings-in-ntrip-clients\/","og_locale":"en_US","og_type":"article","og_title":"NMEA GGA Strings in NTRIP Clients","og_description":"What are NMEA-183 GGA sentences? 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